THE ANALYSIS OF ROCKEr PROPELLANTS

BY CARroN-lJ NMR/

Michael Mei-kung,Ku

Thesis submitted to the Graduate Faculty of the

Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

APPROVED a

J. G. Ma.son

MASTER OF SCIENCE

in

Chemistry

H. M. Ball, Chairman

August, 1977 Blacksburg, Virginia

?. . . • H. C. Dorn

To My Parents

11

ACKNOWLEDGEI1ENTS

I, hereby, express my great appreciation towards by research

advisor, for his ideas, encouragement and help in

this research. I would also like to thank, heartily,

and for their valuable consultations.

I am in debt to for his technical help on the

spectrometer.

The financial support f:rom the u. s. Army Research Office is

appreciated.

iii

TABLE OF CONTENI'S

Page

GENERAL INI'RODU<::rION • • • • • • • • • • • • • • • • • • • • • • 1

PARI' I. POLYBUI'ADIENES • • • • • • • • • • • • • • • • • • • • 3

Introduction • • • • • • • • . • , • , • • • • • • • • • • • 3

Histori~al • • • • • • • • • • • • • • • • • • • • • • • • 7

Experimental • • • • • • • • • • • • • • • • • • • • • • • 9

Results and Discussion • • • • • • • • • • • , • • • • • • 11

Spectral Analysis of Saturated Carbon Region of IIl'PB •• Spectral Analysis of Unsaturated Carbon Region of

Hl'PB • • • • • • • • • • • • • • • • I I I I I • • • Distribution of Structural Units in Hl'PB • • • • • • • • Carbon-13 Nagnetic Resonance Analysis of Hydrogenated

lII'PB • • • • • • • • • • • • • • • • I • • • • • • •

Branching Investigation of Hl'PB • • • • • • • • • • • • Analysis of CI'PB and PBAA • • • • • • • • • • • , • • •

Summary , • • • • • • • • I I I I I I I I I I I I I I I I I

PAR!' II. NITROTOLUENES • • • • • • • • • • • • • • • • • • • •

Introduction I I I I I I I I I I I I I I I t t I I I I I I

Experimental I I I t I I I I I I I I I I I I I I I t I I I

Results and Discussion I I t I I I I I I I I I I I t t t t

11

24 47

53 61 62

72

73

73 74

75

Spectral Assignments of Nitrotoluenes • • • • • • • • • 75 Utility in Mixture Analysis • • • • • • • • • • • • • • 83 Regression Analysis on Spectral Data of Nitrotoluenes. • 84

Summary • • • • • • • • • I I I I I I I I I I I I I I t • • 91 PAR!' III. MISCELLANEX>US COI1POUNDS • • • • • • • • • • • • • • • 92

Introduction • • • • • • • • • • • • • • • • • • • • • • • 92 Experimental • • • • • • • • • • • • • • • • • • • • • • • 94 Results and Discussion • • • • • • • • • • • • • • • • • • 95

iv

TABLE OF CONTENTS (CONTINUED)

BIBLIOGRAPHY • • • • • • • • • • • • • • • • • • • • • • • • • •

APPENDIX • • • • • • • • • • • • ••• • • • • • • • • • • • • • • vrrA ••• • • • • • • • • • • • • • • • • • • • • • • • • • • • AB=lTRAar

v

Page

100

102

106

LIST OF TABLES

Table Page

1. Carbon-13 Chemical Shift Parameters for Paraffins • • • • • 14

2. Corrective Parameters for Anistropic Effect of Double Bond • • • • • • • • • • • • • • • • • • • • • • • , • • 15

3. Comparison of Theoretical Carbon-13 Spectral Datas of Saturated Carbons in Hl'PB with Experimental Data • • • • 25

4.

6.

Carbon-13 Chemical Shift Para.meters for Alkenes •••• • •

Comparison of Theoretical Carbon-13 Spectral Datas of Unsaturated Carbons in HI'PB with Experimental Data • • •

• • • Chemical Shifts (in ppm) of Major Peaks of Polymers •

Carbon-13 Chemical Shifts of Ni trotoluenes • • • • • • • • 8. Coupling Constants Between Ca.rbon-13 Nuclei and Protons

48

63

77

in Substituted Benzenes • • • , , , • • , , • • • • • • , 82

Carbon-13 Chemical Shift Para.meters of Hethyl and Nitro Groups for Aromatic Carbons in Substituted Benzenes •

10. Simplified Carbon-13 Chemical Shift Parameters of .Methyl and Nitro Groups for Aromatic Carbons in Substituted

• • 87

Benzenes • • • • • • • , • • • • • • • , • , • , • • • • 88

11. Simplified Ca.rbon-13 Chemical Shift Parameters of Methyl and Nitro Groups for Aromatic Carbons in Substituted

12.

13.

14.

15.

Benzenes • • • • • • , • • • • • • • • • • • • • , • • •

Ca.rbon-13 Chemical Shift Parameters of Nitro Groups on Methyl Group in Nitrotoluenes ••••••••••• • • •

Carbon-13 Chemical Shifts of Aliphatic Ni tra.te Esters • • • Carbon-13 Chemical Shifts of Some Carboranes • • • • • • • Carbon-13 Chemical Shifts of Some Plasticizers • • • • • •

16. Carbon-13 Chemical Shifts of Some Stabilizers in Double-

90

96

97

98

Base Propellants • • • • • • • • • • • • • • • • • • • • 99

vi

.J

Lisr OF FIGURES

Figure Page

1. Proton NMR Spectrum of Hl'PB • • • • • • • • • • • • • • • • 12

2. Ca.rbon-13 NMR Spectrum of Hl'PB • • • • • • • • • • • • • • 13

J, Ca.rbon-13 Spectral Region of Saturated Carbons in Hl'PB • • 22

4. Unsaturated Carbon Region of Hl'PB , , • • • • • • • , , , • JO

.5. Unsaturated Carbon Region of 1,4 units in Hl'PB 0 I 0 • • • 46

6, Carbon-lJ NMR Spectrum of Hl'PB (Y scale expansion = .5) • • .52

7. Carbon-lJ NMR Spectrum of Hydrogenated HI'PB , , • • • • • • .54 . 8. Carbon-13 NMR Spectrum of Hydrogenated Hl'PB

( Y expansion = 10) , • • , • • • • • • • • • • • t 0 0 I .5.5

Methylene and Methine Carbon Region of Hydrogenated l!rPB • , , • • • • , • • • • • • • • • • • • • • • I • t .59

10. Methylene and Methine Carbon Region of Hydrogenated HI'PB (Y expansion = 10) •••• , • • • • • • • • • • • • 60

11. Ca.rbon-13 NMR Spectrum of Cl'PB • • • • • • • • • • • • • • 64

12. Carbon-13 Spectral Region of Saturated Carbons in Cl'PB • • 6.5

lJ.

14.

1.5.

16.

17.

Unsaturated Carbon Region of Cl'PB • • • • • , • • • 0 I • • 66

Unsaturated Carbon Region of 1,4 units in c:rPB • • • • • • 67

Carbon-13 mm Spectrum of PBAA • • • , • • • , , • • • • • 68

69 Ca.rbon-13 Spectral Region of Saturated Carbons in PBAA • • Unsaturated Carbon Region of PBAA • • • • • • • t I I I t • 70

18, Unsaturated Carbon Region of 1,4 units in PBAA , • , • , • 71

Ca.rbon-13 NMR Spectrum of J,4-Dinitroluene , • • • I I • • 78

20, Carbon-13 NMR Spectrum of Aroma.tic Carbons in 3,4-Dini troluene • , • • • • , • • • • • • • • • • • • • 79

vii

Figure

21.

22.

Ca.rlx>n-lJ NMR Spectrum of Aromatic Carlx>ns in J,4-Dinitroluene (Proton-coupled) ••• , ,

Ca.rlx>n-13 NMR Spectrum of Aromatic Ca.rlx>ns in J,4-Dinitroluene (Proton-coupled) • • • • ,

viii

Page

• • • • • • 80

• • • • • • 81

GENERAL INTRODUcrION

The purpose of this research was to investigate the suitability

of carbon-lJ Fourier transform nuclear magnetic spectroscopy for the

qualitative and quantitative analysis of compounds used in propellants

for solid-fueled rocket motors. An ideal propellant is a stable mix-

ture of oxidizing agents (commonly referred to as oxidizers) and

reducing agents (commonly referred to as fuel), which when ignited

yields hot low-molecular-weight gases in a controlled manner. The

release of these gases through the exhaust nozzle of the rocket motor

provides the desired thrust for rocket propulsion.

The oldest solid propellant is black gunpowder, which consists

of approximately' 15 % charcoal, 10 % sulfur and 75 % potassium nitrate

by weight. A major break-through in solid propellant development in

1890 was Nobel's invention of double-basa propellant, in which nitro-

glycerin was absorbed and desensitized by nitrocellulose. The pro-

pellant was so named because of its tno individual explosive components,

which was mixed so well that the propellant could be considered as a

homogeneous solution of nitroglycerine in nitrocellulose.

It was not until 1945 that composite propellants made their first

appearances. Basically, a composite propellant consists of a crystal-

line oxidizer and possibly a metal or metal hydride additive with a

sufficient amount of binder to hold the propellant together and give

adequate mechanical properties. Unlike the double-base propellants,

composite propellants are inhomogeneous a.s the fuel and oxidizer exist

in separate particles. Particle sizes of fuel and oxidizer, and the

1

2

degree of mixing play an important role in the dete:rmination of the

performance of the propellant.

Previous work in the analysis of solid propellants has involved

gas chromatography, liquid chromatography, mass spectrometr.f, infra-red

spectroscopy, and proton magnetic resonance. F.a.ch of these techniques

has its limitations. While gas chromatography and mass spectrometry

offer superb sensitivity, they are only applicable to volatile samples.

Since the polymers employed in the present study have virtually no

volatility, these techniques would oo of limited utility 1n this study.

In liquid chromatography, the problem of sample volatility is solved,

but even the present state-of-art liquid chromatography does not permit

the positive identification of each of the isomeric dinitrotoluenes and

trinitrotoluenes. Besides, identification with retention indexes is

not alw~s foolproof. For the polymers and ni trotoluenes of the present

study, the low resolution of infra-red and proton magnetic resonance

lead to difficulties in qualitative and quantitative analysis.

While ca.rbon-13 magnetic resonance spectroscopy does not offer

sensitivity comparable to the above mentioned techniques, it does pro-

vide highest spectral resolution. Positive identification of each of

the isomeric dinitrotoluenes and trinitrotoluenes is possible with

ca.rbon-13 magnetic resonance spectroscopy, but not with any one of the

mentioned techniques. The lack of sample volatility is not a problem

in this technique either. Another attractive feature is the possibility

of gel and bllk analysis, which m~ make easy non-destructive analysis

possible.

PARr I. POLYBUTADIENES

INTRODUarION

Since the late 1950's, proton nuclear magnetic resonance has been

employed in the analyses of different types of polymers. However,

in most cases, the resolution in proton magnetic resonance spectra

of polymeric systems is inadequate for detailed analyses of the

polymers. In the case of Hl'PB {Hydroxyl-Terminated-Polybutadiene),

whose spectrum is shown in Figure 1, the only useful information

obtainable is the relative abundance of l,4- and 1,2- units.

The use of carbon-13 magnetic nuclear resonance in analyses of

polymeric systems has a great advantage in resolution over proton

magnetic resonance. This is clearly demonstrated by visual com-

parison of the carbon-13 spectrum of Hl'PB in Figure 2 with its proton

spectrum in Figure 1. Theoretically, the higher resolution of carbon-

13 spectrum is accounted for by the following facts. Ca.rbon-13 spectra

have a greater chemical shift range of typically 5,000 hertz compared

to the 1,000 hertz of proton spectra, both at a magnetic field strength

of 23.5 kilogauss. As dipolar broadening is proportional to the square

of the magnetic moments of the nuclei involved, broadening due to this

effect in carbon-13 spectra should be only one-sixteenth of that in the

case of proton spectra. Spectral complication due to spin-spin coup-

lings of neighboring protons is eliminated because carbon-lJ spectra

are normally obtained as proton noise decoupled spectra. Contribution

of scalar couplings between neighboring carbon-13 nuclei to the spectrum

4

is negligible because of the low abundance of carbon-lJ isotopes in

natural abundance samples.

Carbon-13 magnetic resonance analysis was performed on three

polymers, namelya

HrPB (Hydroxyl-Termina.ted-Polybutadiene)

CfPB (Carboxyl-Termina.ted-Polybutadiene)

PBAA (Polybutadiene-Arcyclic-Acid)

In all three polymers, polymerization was initiated and terminated

with free radicals in such a. way that their average molecular weights

were a.round J,000. As the names imply, lfi'PB a.nd CfPB have hydroxyl

and carboxyl groups as temina.l groups on the polymer chains,

respectively. PBAA is a. copolymer of polybutadiene and a small amount

of a.rcyclic acid; teminal groups are ca.rboxyl groups.

In the polymerization of butadiene, ea.ch individual monomer

may be incorporated into the main chain as one of the following

structural uni ts 1

(a) cis-1,4 unita

(b) trans-1,4 unita

(c) vinylic-1,2 units

-CH CHi-~ I

C=C H H

-C~-CH-

1 CH \\ CH2

,5 I

To a large extent, the physical p:roperties of a polybutadiene, .such

as crystallinity, melting point, elastic moduli, and dielectric

constant are dependent on the distribution of the monomer uni ts in

these three configurations. An attempt was made to detennine the

relative abundance of each of the three structural units and their

occurrence pattern using carbon-lJ magnetic resonance.

The relative abundances of the different structural units can

be determined with infra-red techniques. Silas, Yates and Thorton1

performed the analysis using the characteristic absorption at 10.Jµ.m

of the trans-1,4 configuration, the absorption at 11.0 µ..m of the

vinylic-1,2 configuration, and the broad ba.nd between 12.0 and 15.75

µ. m of the cis-1,4 configuration. The band at 10.J µ. m is attributed

to CH out-of-plane vibration in trans -CH=CH- groups, while the

band at 11.0 µ.mis assigned to CH2 out-of-plane vibration if --CH=CH2 vinylic side groups. 2 The assignment of the broad band between 12.0

and 15.75 fl. m is not straightforward. Hampton, J Binder4 and Richard-

son5 performed similar analyses. However, they assumed that the

absorbance-concentration relationship is linear. This assumption is

equivalent to saying that interactions among various components are

nonexistent. However, the broadband between 12.0 and 15.75 µ m changes

shape and intensity as the cis-1,4 content of the polymer varies.

Secondl.y, accurate determination of absorptivit1es of individual

components at the particular wavelengths requires pure cis-1,4-,

trans-1,4- and vinylic-1,2 polybutandienes which may not be available.

Although the results of these studies appear to be satisfactory, an

6

alternate analytical procedure is desirable to test whether this is

indeed the case.

Since the end groups of the polybutadienes are reacted with a.

cross-linking reagent to provide a. glass which serves as a support

for the rocket propellent, the degree of branching in the polymer

as well as the analysis of the end groups is of interest.

HISTORICAL

Duch and Grant6 found that the carbon-lJ spectral. data of

cis-1,4 and trans-1,4 polytuta.dienes as well as cis-1,4 and trans-1,4

polyisoprenes are consistent with. the structural units arranged in

a stereoregular head-to-tail sequence, and can be interpreted in

te:rms of a single repeating unit. They also found out that spectral.

analysis of a polymer above its glass transition temperature yields

a. far-better resolved spectrum with a. much higher signal-to-noise

ratio when compared with a carbon-13 spectrum ta.ken at a temperature

below the glass transition temperature of the polymer. The reason

for this is that the motion of the polymer chains is sufficiently

rapid and extensive in amplitude to effectively average out the

magnetic dipola.r interactions from the magnetic moments of neighboring

nuclei that are normally experienced by a nucleus in a rigid solid,

once the temperature of the polymer is above its glass transition

temperature. Below its glass transition temperature, the motion of

the polymer is restricted.

Mochel? later claimed that there are no cis-1,4-trans-l,4

linkages in a n-BuLi-catalyzed polybuta.diene, and that only "blocks"

of cis-1,4 units and trans-1,4 units separated by vinylic-1,2 units

are found. This was disproved by Clague and van Broekhoven8 who

pointed out that carbon-lJ technique cannot distinguish between the

three types of linkages in 1,4-polybutadiene, which a.re cis-cis,

els-trans and trans-trans, in the aliphatic carbon region due to the

small effect of these linkages on nearby aliphatic carbon nuclei.

7

8

They also showed that incorrect chemical-shift assignments of Mochel's

model compounds together with the invalid application of cyclic

chemical-shift parameters on acyclic systems resulted in his erroneous

conclusion.

With part. of the chemical-shift parameters reported by Grant and

Paul9 together with a few corrective terms of their own, Furukawa,

Ko ba.yashi, Katsuki, and Kawa.goe10 were able to completely assign the

aliphatic region of an "equibina.ry" cis-1,4-vinylic-l,2 polybutadiene.

Conti, Serge, Pini and Porrt11 concluded from the carbon-13 chemical-

shift data in the unsaturated region that "equibinary" polybutadienes

need not consist of regular alternating sequences of cis-trans-

cis-tra.ns-••••••. other research involving the analytical application

of carbon-13 magnetic resonance on polybltadienes have been performed

by Ala.Jd.,12 Furukawa,13 and Thomassin.14

With polybutadienes of varying amounts of vinylic-1,2 units

blt with a roughly constant ratio of cis-1,4 to trans-1,4 units as

well as hydrogenated-polybutadienes from them, Clague, van Broekhoven

and Bl.aa.uw15 obtained a detailed picture of the sequence distribution

of the various structural units in the polymer chain. It is shown

that these units are distributed in an essentially random manner and

that 1,2 units are head-to-tail incorporated. Among all the literature

cited, this is the most complete and detailed paper. Due to the high

average molecular weight of their samples (around 60,000), end group

analysis is impossible. This is, however, possible with our samples

which have an average molecular weight of 3,000.

EXPERIMENTAL

All the polymers, namely Hl'PB, arPB, PBAA and hydrogenated

Hl'PB were dissolved in deuterochloroform to give solutions of

concentrations of approximately 40% weight/volume. Lower concentra-

tions of down to 5% weight/volume were also used, but no improvement

in resolution was obtained. The spectra were run at 55° C instead of

at room temperature to gain resolution. Higher temperatures of up

to 100° C were employed with the use of deuterated dimethylsulfoxide

as internal. lock, but no improvement in resolution was observed,

Since the caroonyl caroons of crPB and PBM were never observed

preswna.bly because of their long relaxation times, spectra width of

all ca.roon-lJ spectra of the polymers was chosen to be 4,000 Hz, which

was more than adequate in covering the resonance frequencies of all

otner types of caroon nuclei in the samples,

In all spectra, 8K data. points were used for spectral data

acquisition, Without any apod1zation, this resulted in a. computer-

limited resolution of 1.0 Hz which was adequate because the resolution

limited by the stability of the spectrometer under long-term averaging

conditions was certainly no better than 1 Hz.

In all spectra, rf pulses of approximately 90° were used, For

proton-decoupled spectra of Hl'PB, arPB, PBAA and hydrogenated Hl'PB,

the pulse repetition time was 1.5 seconds, while a repetition time

of 5.0 seconds was chosen for their proton-coupled spectra,

Approximately 5,000 scans were collected for ea.ch of the spectra..

Note that the spectrometer was not functioning a.t its best during parts

9

10

of this research. For example, proton-irradiating power was sometimes

down from a maximum of 15 watts to a low of 5 watts. As this affected

signal-to-noise ratio significantly, different spectra transfomed

f:rom the same number of scans could bear observable difference in

signal-to-noise ratio.

The Appendix contains comments on spectrometer operating

procedures.

All the chemical shifts reported are referenced to TMS {tetra-

methyl silane). Positive signs indicate downfield direction.

RESULTS AND DISCUSSION

Spectral. Anal.ysis of Saturated Carbon Region of Hl'PBs

The carbon-lJ magnetic resonance spectrum of Hl'PB is shown in

Figure 2, It consists of three main regions, namely saturated

carbons (from 24 ppm to 44 ppm), unsaturated vinylic carbons (from

114 ppm to 155 ppm), and hydroxyl-bearing te:minal carbons (6J-65 ppm).

Spectral assignments on the saturated carbon region (Figure J)

were made with the aid of the following fo:mula which was developed

by Lindeman and Adamss16

4 o (k) • B + E D A + Y NkJ + /:),, Nk4 c s m=2 m sm s s

where 6 (k) is the carbon-13 chemical shift value of the kth carbon, c B , A , Y and 6 are constants, Nk is the number of carbon atoms s sm s s p p bonds away from the kth carbon, Dm is the number of carbon atoms

bonded to the kth carbon atom having m attached carbons, s is the

number of carbon atoms bonded to the kth carbon atom. Table 1 lists

the values of the constants ( B , A , y and 6 ) as a function of s sm s s s and m.

Anisotropic effect of neighboring double bonds were also corrected

for using the parameters reported by Doman, Ja.utelat, and Roberts. 17

Table 2 lists these parameters.

11

10.0 9.0 s.o

* * -CH2-CH=CH-CH2-

CH Cl)

7.0

and

-CH2-CH-I CH* ~H2

6.0 5.0

* • -CH2-CH=CH-CH2-

and * -CH2-CH-

I CH II CH2

-CH -CH-2 I CH II CH * 2

4.0 3.0

Figure 1. Proton 1~ffi Spectrum of HTPB

2.0

* -CHz-rH-

CH II CH2

1.0

TMS

0 ppm

..... I\)

* * -CH2-CH=CH-CH2-

-CH2-~H­* CH

II CH2

__LJ 150

-CH -CH-2 • CH II

*'CH 2

100

Figure 2.

-CH2-0H

• * -CH -CH-

2 ' CH

50

ll CH2

Carbon-13 NNR Spectrum of HTPB

• • -CH2-CH=CH-CH2

TMS

0 ppm

L ....

\,,)

14

TABLE 1 Carbon-13 Chemical Shift Parameters for ParaffinJ6

Para.meter Value, ppm

B1 6.80 A12 9.56 A1J 17.83 A14 25 ·'~8 ~1 -2.99 Al o.49 B2 15.34 A22 9.75 A23 16.70

• A24 21.43 '?12 -2.69

Ai 0.25 B) 23A6 A32 6.60

A33 11.14 AJ4 14.70

l3 -2.07 B4 27.77 A42 2.26

A43 3.96 A44 7.35 't4 o.68

15

TABLE 2

Corrective Parameters for Anisotropic Effect of Double Bond17

Parameter

* * -CH CH-2\ I 2

-CH

c=c H H

\c-~ H \

CH-2

-CH-CH-2 I

fiH ~H2

*carbon Nuclei p to double bond

Carbon Nuclei "d to double bond

Value. ppm

-2.6

).0

1.8

0

-0.5

* This effect can be as large as ± 1 ppm. Because of its variability, it is assumed to be zero.

16 I

As an example, the chemical shift of the carbon of interest,

which is marked with an asterisk, is calculated.

• ••••

Since the carbon atom is secondary, s = 2.

It is bonded to two carbon atoms which are bonded to two carbon

atoms, therefore n2 = 2. The absence of other directly b:>nded carbons

bearing higher substitution makes n3 = n4 = o. The number of carbon atoms 3 bonds away from it is 3, so Nk3 = 3.

The number of carbon atoms 4 bonds away from it is 3, so Nk4 = 3.

Neglecting temporarily the anisotropic effect of neighboring

double bonds, its carbon-13 chemical shift would be 1

oc = 15,34 + 2(9.75) + 3(-2.69) + 3(0.25) = 27.52 ppm

As the carbon atom is in a cis configuration with regards to

the double bond which is one bond away, 2.6 ppm should be subtracted.

Considering that there is another double bond, which is three bonds

away, another 0.5 ppm should be subtracted. This makes the final

calculated chemical shift to be 24.42 ppm.

Assuming that a triad sequence is sufficient to account for the

carbon-13 chemical shift of a carbon atom in the polymer, the chemical

shifts of the carbon atoms in the Structures, labelled "A" through "N"

are calculated. Structures not considered involve the attachment of

17

two v1nyl1c-l,2 units head-to-head or tail-to-tail. For example, a

head-to-head attachment such as

••••••

is highly unlikely. Among the structures, labelled "A" through "N",

the rotation "l,2 unil11 denotes that the methine carbon of the 1,2 unit

is to the right of the methylene carbon. The above illustrated head-to-

head attachment can be denoted as "l, 2 · unit l, 2 unit".

The figures under the column "Pro ba.bili ty" are calculated 'tased

on a random distribution model in which the three types of structural.

units occur in random in the polymer chain according to a certain

relative abundance. The relative abundance of the three types of

structural uni ts are determined from the proton spectrum of Hl'PB, and

its saturated carbon-lJ spectral region (vinylic-1,2 unit = 0.22,

cis-1,4 unit= 0.2.54, and trans-1,4 unit= 0.526). The expected

accuracy of these probability figures is 2 significant figures.

However, for the random distribution model five significant figures

are listed to minimize mathematical errors and for the purpose of easy

checking.

Comparing the theoretically calculated chemical shifts with the

experimentally observed values allows assignment of the peaks in the

structures "A" through "I", except "H". Peak "M" is calculated to

have a chemical shift of 40.42 ppm, which is 2.9.5 ppm upfield from the

experimentally observed peak. However, there is little doubt that

Structure Calculated Probability Chemical Shift in ppm

1,2 unit * 1,2 uni! A - CH2'- ,,cH2-or C=C 24.42 0.055,88

1,4 unit H H

* 1,4 unit

B 1,2 unit ·-CH2., / CH2- . or C=C 27.36 0.396,24 1,4 unit H H

1,2 uni't 1,2 uni? .... c -CH2, H co

or c=e,* 30.02 0.115, 72 .1,4 unit H CH -2

f.2 unit * f.2 unit D -cH2 /CH2-or "c=c 31.62 0.055,88

1,4 unit H H

E 1,2 unit -CH2, H 1,4 unit

or c=c,* 32.96 0.820,56 1,4 unit H CH2

Structure Calculated Probability Chemical Shift in ppm

F 1,4 unit * -CH2yH- 1,4 unit :n.12 0.1:33,848 CH 8H2

* 1,2 unit G 1,4 unit -cH-cH- '.34.47 0.037,752 2 I CH

&2 ..... '°

1,2 unit * 1,2 unit H -CH- CH- '.35.78 0.010,650 2 bH

& 2

~,2 unit ,,

I -CH H Y ,2 unit '.37.22 0.115,72 or 2--.......C=C

1,4 unit H 'cH-2

Structure Calculated Probability Chemical Shift in ppm

* J 1,4 unit -CH2b:- 1,2 unit J?.85 0.037,752

It CH2

* 1,2 unit K 1,4 unit -cH-cH- J?.98 0.0)7,752 I 2 CH 8H2

N 0

L 1,4 unit * -9H-CH2-CH

l,2-unit J8.J5 0.037,752

n CH2

1,2 unit * 1,2 unit M -cH-cH- J8.98 0.010,650 2 tH II CH2

Structure

N 1,4 unit * -CH2-rH-CH HH2

1,4 unit

Calculated Chemical Shift in ppm

40.42

Probability

0.1JJ,848

~

N

50

Fi~re J.

E

B

I

I\ - c IL_ I F,G I

40 JO

Carbon-13 Spectral Region of Saturated Carbons in HTPB

20.ppm

N N

2)

this is assigned correctly, the reason being that this peak appears as

a doublet in the proton-coupled carbon-1) spectrum of Hl'PB, while all

the other peaks of significant 1ntensi ty appear as triplets as predicted

by Structures "A" through "I". Carbon nuclei in structures "H'' and

"M" are expected to yield extremely weak signal. Hence, it is not

surprising that they are not assigned. Structures "J" through "L"

have the side-by-side arrangement of two vinylic-1,2 units, each of

which has a chiral carbon atom. As carlx>n-1) chemical shifts of a

chiral carbon atom and neighlx>ring carbon atoms are sensitive to the

stereo configuration at the chiral center, the magnetic resonance

signals from these structures will probably be split into a number

of small peaks. So the small peaks a.round 41 ppm a.re likely to come

from these Structures.

Peak "B" is a result of the methylene carbons in a cis-1,4 unit

while peak "E" is due to the methylene carbons in a tra.ns-1,4 unit.

Therefore, the relative areas of peaks "B" and "E" should provide

information on the relative abundance of cis-1,4 units and trans-1,4

units in the analyzed HI'PB sample. In this case, the relative abun-

dance of tra.ns-1,4 units and cis-1,4 units is found to be 2.07 to 1.

From the proton spectrum of lil'PB, the polymer is found to contain

22Jt vinylic-1,2 units and 78% 1,4 units, based on the assignment of

-CH==CH- pmton at 5.4 ppm, and -Cl-FCH2 pmtons at 5.0 ppm as well as

5.4 ppm. This assignment was reported by Chen.18 This information

together with the relative abundance of trans-1,4 units and cis-1,4

units enables the calculation of the relative abundances of all three

24 I

types of units. The analyzed Hl'PB sample is thus found to have 25.4% cis-1,4 units, 52.6% trans-1,4 units and 2Zl& vinylic-1,2 units.

Table 3 is a comparison between calculated chemical shifts and

experimental chemical shifts, as well a.s a. comparison between cal-

culated peak areas and observed peak areas of the peaks from the

various structures. The peak area of peak "B" is used as a reference

to convert calculated probability to calculated peak area.

Spectral Analysis of Unsaturated Carbon Region of ID'PB

Roberts and co-workers17 found that the carbon-13 chemical shifts

of unsaturated carbon a.toms correlates linearly with the number of

carbon a.toms at different positions, which are defined with respect

to the carbon a.tom marked with an asterisk in the compound below as

a 13 Y a' 13', and y•. ' , ' ,

* c - c - c - c = c - c - c - c Y 13 a a• S' Y'

With ethylene (123.3 ppm) as a reference, the chemical shift of

an unsaturated carbon atom can be calculated using the formula.:

where 6. is the carbon-13 chemical shift of the unsaturated carbon

atom, ~· n2, n3 , n4 , n5, and n6 are the number of carbon atoms at

the positions a, s. y, a•, s•, and y•, respectively.

They also found out that in the case of a 1, 2-disubsti tuted

ethylene, the cis configuration of the double bond shifts the chemical

25

TABLE J

Comparison of Theoretical Carbon-13 Spectral Datas of Saturated Carbons in HTPB with Experimental Datas

Structure Calculated Observed Calculated Observed Chemical Chemical Peak Area Peak Area Shift Shift in ppm in ppm

A 24.42 24.85 5.0 5.1

B 27.36 27.42 J5.1 J5.1

c J0.02 J0.02 10.3 8~9

D 31.62 * N .A. 5.0 N .A.

E 32.96 J2.62 72.7 75.4

* 33.98 F J'.3.72 11.9 • 18.9

G 34.47 33.98 J.4

H 35.78 N.A. 0.9 N .A.

I 37.22 38.10 10.3 8.2

J 38.35 N.A. 3.3 N .A.

K 37.85 N.A. 3.3 N.A.

L 37.98 N .A. 3.3 N .A.

M J8.98 N .A. 0.9 N .A.

N 40.42 43.37 11.85 13.0

• "F" and "G" overlap

*Not assigned

26

shift of the unsaturated carbon a.tom by 1.1 ppm in an upfield

direction. These parameters a.re listed on Ta.ble 4.

The ca.rbon-13 chemical shifts of the unsaturated carbons in the

following structures, la.belled "0" through "X" are calculated using

the above parameters reported by Roberts and co-workers. In addition,

the anisotropic effect of double bonds three bonds away a.re corrected

for by subtracting 0.5 ppm from the calculated chemical shift; just

like it is done in the saturated carbon atoms previously.

The structures labelled "O" through "X" are the identical struc-

tures labelled "A" through "N" considered previously 1n the saturated

ca.rbon region of HI'PB. However, the carbons of interest are different.

The probability of occurrence of the carbons of interest in these

structures is calculated using the relative abundance of the three

types of structural uni ts found in the proton spectrum, and the

saturated carbon region of Hl'PB.

Within the ten structures la.belled "0" through "X", "R" and "S",

"T" and "U" have identical calculated chemical shifts of 130. 3 ppm

and 131.4 ppm, respectively. So eight lines a.re expected in the

unsaturated carbon region of the spectrum. Indeed, eight lines a.re

observed when the spectrum is run at room temperature. However, when

the spectrum is run at 55° C, these eight lines shown additional

detail. Groups of three lines are observed for structures "P", "Q",

"R" and 11S", "T" and "U". The line-shapes of structures "V" and "W"

suggest that they are a.lso groups of three lines. Addi tiona.l f ea.tures

a.re also observed for lines "0" and "X", but not sufficient for

further discussion.

TABLE 4 Carbon-13 Chemical Shift Parameters for Alkenes17

Parameter Value, ppm

oJ.. 10.6 f3 ?.2 (J -1.5

0(.) -7.9

{3 J -1.8 '(/' 1.5

cis -1.1 3 bonds away from another -0.5 double bond

Structure Calculated Probability Chemical-shift in ppm

0 1,2 unit -CH2yH- 1,2 unit 114.8 0.220,000

or or 1,4 unit ftH 1,4 unit

*CH 2

1,2 unit p -CH2"C~CHZ 1,2 unit 128.8 0.055,880 or

H H 1,4 unit

1,2 unil I\>

-CH2'b~ 1,2 unit 129.9 0.115,720 CD

Q or H "ctt- 1,4 unit 2

R 1,4 unit -CH2 * /CH2- 1,2 unit 1JO.J 0.198, 120 'C=c or

H H 1,4 unit

s 1,4 unit -CH2 * CH2- 1,2 unit 1)0.J 0.198, 120 'c=V or

H H 1,4 unit

Structure Calculated Probability Chemical-shift in ppm

1 ,2 unit

T 1,4 unit -CHZ--....* H 131.4 0.410,280

C=C-......._ or H CH- 1,4 unit 2

1 ,2 unit 1,4 unit -CHz"c-~ 131.4 o.410,280 u or H * "'-cH- 1 ,4 unit 2

1,2 uni:£ 1 ,2 uni? -CH2 */CH2 131.8 0.055,880 l\) v -.a 'c=-c or

H H 1 ,4 unit

1,2 unit 1 ,2 unit -CH H 1'.32. 9 0.115, 720 w 2'c=c, or H * CH2- 1 ,4 unit

x 1,2 unit -~t-

1,2 unit 145.J 0.220,000 or * H or

1,4 unit I 1,4 unit 2

T,U

R,S

I

r . w! ii~~\ ~ .·~ vuij vp~~~..-v....,,....-

150 140 130 120

Figure 4. Unsaturated Carbon Region of HTPB

0

110 ppm

' '-'> 0

Jl

To account for these groups of three lines, it is assumed that

the chemical shift of a unsaturated carlx:m atom in a 1,4 unit is a

function of both substituent effect as well as the sterlc interaction

between the groups attached to both ends of the 1,4 unit. It is also

presumed that a 1, 2 unit has more steric interaction with another

unit at the other end of the central 1,4 unit because of its vinylic

side-branch, compared with the steric interaction of a 1,4 unit with

the same unit. Perhaps it is a little surprising to note that a carbon

atom can "feel" the stereo configuration located at four to five bonds

away, but this has been observed by Clague and co-workers15 by the use

of model compounds. Besides, from the data in another pa.per published 8 by Clague and co-workers, it is evident that c2 in tra.ns-4-olefins

is consistently to higher fields that c2 in the corresponding cis-4-

olefins.

Structure "P" is composed of three micro-structures as shown on

page J4. Based on substi tuent effect alone, all three micro-structures

should have identical chemical shifts. However, considering the steric

interaction of the 1,2 unit attached to one end of the central cis 1,4

unit to be different in each case with the three different units

attached to the other end of the central cis 1,4 unit, there should be

three lines. This accounts for the group of three lines observed at

127.53 ppm, 127.71 ppm, and 127.86 ppm.

An inspection on the three micro-structures of "Q" (page 35) shows

that the three lines at 128.0J ~pm, 128.22 ppm, and 128.)9 ppm arise

from the different steric interactions of the vinylic 1,2 unit with

32

the three different structural uni ts attached at the other end of the

central trans-1,4 unit, similar to the case of structure "P".

Some micro-structures in structures "R" and "S" (page 36-39)

are duplicated. Micro-structures "R. " and "S " "R " and "S " "R " -o b ' c e ' e and "Sc", "Rf" and "Sr" are identical structures. The reason for

replication is to keep a symmetry of six micro-structures in each

structure. The probability of occurrence of such a carbon in the

replicated micro-structures is halved in order to make the total

probability equal to the probability of occurrence if the micro-

structures are not duplicated.

In the micro-structures of structures "R" and "S", one of the

structural units attached to the central cis-1,4 unit is always

a 1,4 unit which should have smaller steric interaction with the other

unit attached to the central cis-1,4 unit. As a result, some of

these micro-structures may be non-resolvable.

Ra, Rb, Rc, Sb, and Se are not resolved. The resulting line is

denoted as "11:"• with probability= 0.114,842.

Rd, Re' Rf, Sc' and Sf are not resolved. The resulting line is

denoted as "R:rr"• with probability= 0.237,815.

Sa and Sd are not resolved. The resulting line is denoted as

"R111", with probability= o.043,587.

The three lines from structures "T" and "U" are accounted for

similarly.

Ta, Tb, T0 , Ub and Ue were not resolved. The resulting line is

denoted as 11T111

, with probability= 0.2J7,81.5.

33

T , T , T , U , and Uf are not resolved. The resulting line is d e f c . denoted as "T II" , with probability "" 0. 49 2, 48 5.

Ua. and Ud are not resolved. The resulting line is denoted as

"TIII"' with probability= 0.090,262.

Again as in the case of structures "R" and "S", there are

replicates of micro-structures. Micro-structures b, c, e, and f of

structure "T" a.re identical to the micro-structures b, e, c, and f of

structures "U", respectively.

In structure "V", one of the structural uni ts attached to the

central cis-1,4 unit is always a 1,2 unit. However, the 1,2 unit

is further away from the unsaturated carbon of interest, compared

with the situation in structures "P" and "Q". As a result, a slightly

broader, poorly-resolved line is observed instead of the three lines

observed in the case of structures "P" and "Q".

The same reasoning is employed to account for the line from

structure "W".

Since all the carbon atoms in the micro-structures of structures

"P" through "W" are unsaturated carbons of 1,4 uni ts which are in the

"back-bone" of the polymer, it is reasonable to assume that they have

very similar line shapes due to the similarity of environments. As a

result, a reasonable correlation between peak heights of these micro-

structures and the relative abundance of the carl:x:m atoms in the

different micro-structures is expected.

In Table 5, the probability of occurrence of a particular carbon

atom is converted to peak height using the peak at 129. 31 ppm as a

Micro-structure of Structure "P" Calculated Probability Chemical-shift in ppm

1,2 unit 1,2 uni? 0 -CH2'..* /CH2 128.8 0.012,294 c=c H H

6 1,2 unii -CH2'..* /CH2 cis 1,4 unit 128.8 0.014,194 c=c H H

c 1 ,2 unil -CH2"-C /CH2- trans 1,4 unit 128.8 0.029,393 =C '$

H H

Micro-structure of Structure "Q11 Calculated Probability Chemical-shift in ppm

1,2 unit 1,2 uni~ a -CH2'.* H 129.9 0.025,458 c=c"c H H-2

b 1,2 unit -CH2"* H cis 1,4 unit 129.9 0.029,393 c=c" H CH-2

1,2 uni? \,,.) c -CH2........._* H trans 1,4 unit 129.9 0.060,869 \J\ C=C H "cH-2

Micro-structure of Structure "R" Calculated Probability Chemical-shift in ppm

a cis -CH~ /CH2- 1,2 uni~ 130.3 0.014,194 1 ,4 unit -C

H H

b cis -CH2'''c=c/CH2- cis 130.3 0.016,387 1 ,4 unit 1,4 unit

H H

c cis - CH2......_ * /CH2- trans 130.3 0.0:33, 935 1,4 unit C=C 1 ,4 unit ~

H H

Micro-structure of Structure "R" Calculated Probability (Continued) Chemical-shift

in ppm

d trans -- CH2"-* /CH2- 1,2 unit 1JO.J 0.029,J9J 1,4 unit C=C

H H

e trans - CH2"-... * /CH2- cis 1JO.J O.OJJ,935 1,4 unit c~c 1,4 unit

H H

f trans -cH2 * ~H2- trans 1JO.J 0.070,276 1,4 unit 'c==C 1,4 unit ~

H H

Micro-structure of Structure 11 511 Calculated Probability Chemical-shift in ppm

cis -CH2"c=c/112 1,2 unit 130.3 0.014,194 a 1,4 unit H H

b cis -CH2 */CH2- cis 130.3 0.016,387 1,4 unit "c==c 1,4 unit

H H

cis -CH2"'-.. */CH2- trans 130.3 0.033,935 c 1,4 unit C=C 1,4 unit ~ H H

Micro-structure of Structure "S" Calculated Probability (Continued) Chernical-shif t

in ppm

d trans - CH2, * /CH2- 1,2 unit 130.J 0.029,393 1,4 unit C=-C

H H

e trans -CH2 C/CH2- cis 130.3 0.033,935 1,4 unit 'c= 1,4 unit

H H

f trans -CH2, VCH2- trans 130.3 0.070,276 1,4 unit C= 1,4 unit \...)

- 'CJ H H

Micro-structure of Structure "T" Calculated Probability Chemical-shift in ppm

cis -CH2"-* H 1,2 unit 131.4 0.029,393

Q 1,4 unit c=c H "CH 2

b cis -CHZ"-* H cis 1'.31.4 0.033,935 1,4 unit c=c 1,4 unit

H ""-cH-2

cis -CH2"'-..* H trans 1)1.4 0.070,276 ~ 0 c 1,4 unit c=c"ctt 1,4 unit

H -2

Micro-structure of Structure "T" Calculated Probability (Continued) Chemical-shift

in ppm

d trans -CH2"-.....* H 1,2 uni~ 131.4 0.60,869 1,4 unit C=C"c

H H-2

trans - CH2""-.* H cis 131.4 0.070,276 e 1,4 unit e=.c 1,4 unit H ""-cH-2

f trans - CH2......._* H trans 131.4 0.145,532 ~ 1,4 unit c==c......_ 1,4 unit H CH -2

Micro-structure of Structure "U'' Calculated Probability Chemical-shift in ppm

cis -CH H 1,2 unit 131.4 0.029,393 Q 1,4 unit 2"'-c=c ""-

H * CH-2

cis -CH H cis 1)1.4 0.033,935 b 1,4 unit 2"-c=-c"- 1,4 unit

H * CH-2

cis -CH2........._ H trans 131.4 0.070.276 ~ N c 1,4 unit c=c 1,4 unit

H * "-cH-2

Micro-structure of Structure "U" Calculated Probability (Continued) Chemical-shift

in ppm

d trans -CH2"-. H 1,2 unif 131.4 0.060,869 1 ,4 unit C=C

H * ""-cH -2

e trans -CH H cis 131.4 0.070,276 1 ,4 unit 2'-..C=C 1,4 unit

H * ""-cH-2

f trans -CH H trans 131.4 0.145,532 -~

Z"'-c=c \,,.)

1,4 unit H * "-cH-

1,4 unit 2

Micro-structure of Structure "V" Calculated Probability Chemical-shift in ppm

a 1,2 uni'? -CH2'-c=t/CH2 1,2 uni? 131.8 0.012,294

H H

b 1,2 uni? -CH2~cH2- cis 131.8 o.01'f,194 1,4 unit

H H

c 1,2 unit -cH2 */CH2- trans 131.8 0.029,393 i 'c==c 1,4 unit H H

Micro-structure of Structure 11W11 Calculated Probability Chemical-shift in ppm

1,2 uni.{ -cH2'- H 1,2 unit 132.9 0.025,458 Q c=c

H *"cH-2

b 1,2 unit -CH2'-.... H cis 132.9 0.029,393

C=C 1,4 unit H *"cH-2

1,2 uni~ 0.060,869 .;:-

-CH H trans 132.9 - \J\

c 2'---.C=C 1,4 unit H * "-cH -2

T,U

~ R,S

w v Q

1'.34 1)0 127 ppm

Figure 5. Unsaturated Carbon Region of 1,4 units in HTPB

47

reference. As observed, there is indeed good correlation between

predicted and observed peak height. Peak "V" at 1JO.J6 ppm is on the

tail of peaks from "T" and "U", resulting in a higher-than-predicted

peak height.

Distribution of Structural Units in HI'PB

The incorporation of monomeric l,J-butadiene as one of the three

types of structural units during polymerization can be viewed as the

copolymerization of three different types of vinyl monomers. The

process of copolymerization can be described with a Narkoffian

statistical model. In order to have some understanding of the Markoffian

statistics, a few cases of the Markoffian statistics are defined. In

a third order case, the terminal radical, the penultimate monomer,

and the next preceding monomer all affect the addition of a new

monomer to the growing chain. In a second order case, the growth of

the chain is affected by the terminal radical and the penultimate

monomer. In a first order case, only the terminal radical has an

effect on the growth of the polymer chain. A special case in the

Markoffian statistical model is the zeroth order case in which the

chain growth is affected not by anything in the polymer but only by

the relative abundance of the different types of monomers. This

special case of Harkoffian statistics reduces to Bernoulian statistics,

which is a description of completely rand.om distribution of different

monomeric units in the polymer chain.

The analyzed lil'PB appears to follow Bernoulian statistics. This

is supported by the good agreement between the calculated peak areas

48

TABLE 5

Comparison of Theoretical Ca.rbon-lJ Spectral Data of

Unsaturated Carbons in HI'PB with Experimental Data

Calculated Observed Chemical- Chemical-

~licro- shift shift Calculated structure in ppm in ppm Peak Height

128.8 1Z?.5J 1.5 p 128.8 127.86 1.7

128.8 127.71 J.6

129.9 128.0J J.l Q 129.9 128.39 J.6

129.9 128.22 7.4

lJO.J 129.lJ 5.2 R, S 130.J 129.50 lJ.8

lJ0.3 129.31 28.5

131.4 129.72 10.8 T, U lJl.4 130.00 28.5

131.4 129.89 59.0

131.8 130.36 1.5 v 131.8 lJ0.36 1.7

131.8 lJO.J6 J.6

132.9 lJl.lJ J.l w lJ2.9 lJl.lJ J.6

lJ2.9 lJl.lJ 7.4

:f: Not Assigned

Observed Peak Height

2.0 2.0 J.5

2.5 3.0 7.0

6.o 14.o 28.5

11.9 31.4 60.0

+N.A. N.A. 7.0

N.A. N.A. 8.0

and the observed peak areas in the saturated carb:m-13 spectral region.

A much more convincing evidence is the sets of three lines in the

unsaturated spectral region which shown the relative abundance of

different triad distributional sequence of different structural units.

Since the peak-height ratios between the three lines in each set are

identical within experimental errors, the distribution of the struc-

tural units within the polymer chain must be completely random.

As the Hl'PB sample was prepared by free-radical mechanism,

Bernoulian statistical description of the structural units is expected,

because the configuration of the ultimate unit is not decided until

further addition occurs, that is,

-CH I 2'\. H

c = c H \

CH• 2

+ CH2 = CH - CH = CH2 )

+CH =CH-CH= CH 2 2 >

+ CH = CH - CH = CH -> 2 2

cis-l,4 structure

vinylic-1,2 structure

vinylic-1,2 structure

trans-1,4 structure

50

Hart and Meyer19 reported that polymerization of butadiene by

free radicals yields about 20% of vinylic-1,2 units, whose abmdance

is relatively independent of temperature, and that the trans-1,4 units

alw~s outnumber the cis-1,4 units but their relative amount va.rles

with temperature. At 100° C, a composition of 18% vinylic-1,2 units,

JO% cis-1,4 units, and 52% trans-1,4 units is reported. This compo-

sition is very close to the composition (22% vinylic-1,2 units, 25.4%

cis-1,4 units and 52.6% trans-1,4 units) determined earlier for the

analyzed HrPB sample.

If the polymer were synthesized via ionic mechanism, Harkoffian

statistical description of structural unit distribution would be

expected because a monomer in the polymerization process has to come

between the charged chain end as well as its attendant counter.ton

which subject a powerful and directed polarizing field. The effect

of the influence is sensitive to the degree of dissociation of the

counter.ton from the chain end and hence to the dielectric constant of

the medium and its solvating power. 20 Randall and co-workers observed

an increase in vinylic-1,2 addition in polybutadiene as a result of a

more polar reaction medium in an ionic polymerization process using

butylli thiwn catalyst. Conti and co-workers11 prepared polybuta-

dienes with ionic catalysts. The unsaturated carbon peaks of the

1,4 units in these polymers show fine structures similar to the ones

in the spectral analysis of unsaturated carbon region of HrPB. How-

ever, the peak-height ratio va:r:y among the sets of lines, indicating

that the distribution of structural units in their samples is not

completely random.

Investigation of End-carbons in Polymer-chain

After expansion of the Y scale of HI'PB spectrum, two lines of

low intensities appear at 6J.O ppm and 64.9 ppm. These two lines are

likely to come from the terminating carbon atoms of the polymer chain

bearing a hydroxyl group. The chemical shifts of hydroxyl-bearing

carbon atoms of several possible structuxes a.re calculated.

structure

* CH - OH

Calculated Chemical Shift, ppm

A c I ~

B

c

D

H

* -CH - CH - OH 2 I

*

CH II CH2

-CH - CH2 - OH & II CH2

64.59

?J.50

52

-----~§:

~ ----""'"? 0

0 0 .....

.53

Ro berts21 found simple linear correlations with standard devia-

tions of + 1. 0 ppm between the carl:on chemical shifts of alcohols and

the corresponding hydrocarbons wherein a methyl group takes the place

of the hydroxyl group. The correlation found is:

0ROH s = o.aJ o~H3 + 43.J ppm

0ROH = c2

0RCH3 c2 + 0.5 ppm

0ROH = 0RCHJ - 1.7 ppm C3 CJ

where o~~H; is the chemical shift of nucleus "i" in the analogous 1

methyl compound.

Inspection of the calculated chemical shifts in structures "A"

and "C" shows that they do not correlate well with the observed values.

Therefore, it seems likely that the two lines comes from structures

"B" and "D".

Additional information concerning these end groups was obtained

from spectral analysis of the hydrogenated polymer. This is discussed

in the following section.

Carbon-13 :Magnetic Resonance Analysis of Hydrogenated Hl'PB

In order to gain fUrther information on the microstructure, the

polymer was catalytically hydrogenated with 10% palladium on char-

coal under 800 pounds pressure, with 0.1 gram of catalyst used for

'i-

ll U TMS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~_j\,.JW\.__/ ~~~~~~ l__ r , , , , 1 • L __ _ • ______ L_ 1 , • • • , 150 100 50 0 ppm

Figure 7. Carbon-13 m-rR Spectrum of Hydrogenated HTPB

55

it a ..:t~ P.

{ 0 ,......,

j 0 ..-i

) II s::

f 0 .... II) s:: _ff a

"" :-< ~ Q)

~ >-t ->- i:.n p...

-=s: ~ ~ -~ 'O

Q) ~ ~ ~ 0 n1 .S"' \l'I s::

=:[. Q) tll)

..>'r;- 0

~ S.. ;.; ~ ~ ::r: ~ ~

~ 0

fi_ g ~ ~

~ (.) (),)

~~ u. = ... U'l -x:_ ~~~i P1 -~--~ ~ ~ ('°'\

1E: ..-i

it 0 I 0 s::

$.~ ..-i 0 -t- ~ lt. rd

* u

~ ~ ..... _.,_ . .... ex:> ~ ~ Q)

~ J.. ~ 3:- •n ............. ~ ~ ..

...Z:L _,. .. ~ 2 s;. ~

~ -;;:l:-'.E-- 0 ff \{'\

..-4

every gram of Hl'PB. As Hl'PB was not significantly soluble in ethanol

or other common alcohols, hexane was used as a solvent. Hydrogenation

was complete within two to three hours, as observed by the drop in

hydrogen pressure.

After the removal of unsaturation in the structures labelled

"A" through "D" on page 51, the predicted chemical shifts of the

hydroxyl-bearing carbons will be 62.10, 62.10, 72.01, and 65.64 ppm,

respectively. Two peaJrn of low intensities were observed at 64.9 ppm

and 65.5 ppm of the carbon-13 spectrum of the hydrogenated compound.

The lines clearly ruled out that they came from structures "A" and

11 B11, because only one line would be observed in such a case after the

removal of cis and trans isomerism through hydrogenation. Based on

the successful correlations of calculated and o bscrved chemical shifts

on the other carbon atoms in the polymer, it seems likely that the

structures, "B" and "D" give rise to the two observed lines.

The other peaks in the carbon-lJ spectrum of the hydrogenated

polymer axe assigned to the carbon atoms in the following structures.

Only these four structures are considered as other structures

should have negligible contribution to the spectrum, based on the

information obtained from the parent polymer. The calculated chemical

shifts of the carbon atoms in these structures are tabulated below:

Carbon Atoms

I

II a IIb

Calculated Chemical Shift, ppm

29.96

11.37 27.16

57

Structure I

-CH-CH -cH-cH -2 2 2 2

Structure II

Structure III

Structure IV

d e f c g h i -(CH - CH - CH -CH )-CH·- CH- CH- CH-(CH -cH -cH -CH )-2 2 2 2 2 1 2 I 2 2 2 ·2

b CH2 CH2 a dHJ bHJ

Carbon Atoms

IIc I Id IIe I If Ilg IIh

IIIa IIIb IIIc II Id IIIe II If IIIg IIIh IIIi IIIj IIIk

IVa I Vb IVc IVd IVe IVf IVg IVh IVi

58

Calculated Chemical Shift, ppm

27.52 29.96 29.96 30.21 J4.22 .39.12

11.37 27.16 27 • .52 27.52 29.96 29.96 J0.21 J0.46 34.22 J4.22 39.12

11.37 27.41 27.52 29.96 29.96 J0.21 )4.47 37.05 38.48

Based on chemical. shift correlations al.one, the peaks in the

spectrum are assigned as the following:

Carbon Atom

Ila IIb Ile I, !Id, IIe IIf IIIh IIg IVh I Vi IIh, IIIk

Calculated Chemical Shift, ppm

11.37 27.16 27.52 29.96 J0.21 30.46 34.22 37.05 38.48 39.12

Observed Chemical Shift, ppm

10.9.5 26.lJ 26.91 29.78 J0.24 Jo.70 JJ.47 )6 • .50 38.JO 39.12

I, !Id' Ile

~

l rrh rrrk nf IIrlj \ rrc! IIb

____ _____,· ~VUv ---~~~~~~~~

50 40 JO 20 ppm

Figure 9. Eethylene and Eethine Carbon Region of Hydrogenated HTPB

~~W'!~.fvo'c•\~·v) ~Jl 50 40

\ \

I;

~

1(1 I I I

30

I

~"''~~Vvvi

20 ppm

Figure 10. Nethylene and :t-:ethine Carbon Region of Hydroeenated HTPB (Y expansion = 10 )

°' 0

61

The low-intensity peak at )8.30 ppm gives further support to

the random distribution model used in Hl'PB. In the Hl'PB spectru.'U,

evidence of two adjacent 1,2 units are not observed. However, this

is indicated by the peak at 38.30 ppm in the hydrogenated polymer,

which comes from a carl::on atom in a structure with two adjacent

1,2 units.

Branching Investigation on !Il'PB

To investigate branching in !Il'PB, the chemical shifts of the

carl::on atoms at or near tho branch site in the structure shown below

are calculated.

CH - CH = CH - CH ----2 I c

CH - CH - CH - CH -2 \ 2

CH - CH = CH - CH -d a b 2

Calculated Chemical Carbon Atom Shift, pp::i

a

b

c

d

128.8 (cis) 129.9 (trans)

131.8 (cis) 132.9 (cis)

38.52

29.43 (cis) 35.0J (trans)

Inspection in the carbon-lJ spectral region around these calcu-

lated chemical shifts shows no pea.k of significant intensity that

can be accounted for. Therefore, it seems tha.t there is very little

or no branching in the polymer.

62

Analysis of CI'PB and PBAA

The spectra of CI'PB and PBAA with expansions of their saturated

and unsaturated regions a.re shown on pages 64 through 71 • Comparison

of each of the individual spectrum to their corresponding counterpart.

in Hl'PB shows that the spectra of CI'PB and PBAA. are almost identical

to that of HTPB. All the lines in the Hl'PB spectrum, with the excep-

tion of the two lines from hydroxyl-"bearing end carbons, are observed

in the spectra of the other two polymers. Table 6 shows the almost

identical chemical shifts of the corresponding lines of significant

intensities from structures laoolled "A" through "X" of Hl'PB.

In crPB and PBA.A., end group analysis is not possible as the

carbon atoms next to the carboxylic terminal group do not show up

in the spectra for some unk.now-n reason. Other analyses performed on

H.rPB are repeated for CI'PB and PB.\A.

A few "extra" lines are observed in the PBAA spectrum. At first,

they were thought to "be resonances of the arcyclic acid units, but

calculated chemical shifts of arcyclic acid units flanked by 1,4 units

or 1,2 units shows that they are not. The a.mount of arcyclic acid in

PBAA is known to be extremely small, so not. observing their resonance

is not surprising. It is also known that PBAA contains tYPically 8%

impurities which explains the appearance of these "extra" lines.

6J

TABLE 6

Chemical Shifts (in ppm) of Major Peaks of Polymers

Structures HTPB CTPB PBAA

A 24.85 24.97 24.70 B 27.41 27.5J 27.18 C, D 30.02 30.17 29.90 E 32.62 32.81 J2.46 F, G 33.98 34.09 JJ.70 I 38.10 38.25 J?.98 N 43.37 4J.57 43.22 0 114.04 113.97 114.16 tJ 127.71 127.52 127.87 . Q 128.22 128.03 128.37 R, s 129.31 129.07 129.42 T, U 129.89 129.65 130.00 v 130.36 130.93 lJ0.47 vl 131.13 131.32 131.24 x 142.50 142.31 142.66

64

t _J ----======~J

N

50

Figure 12.

E

B

I F,G A

JO 20 ppm

Carbon-13 Spectr<il Region of Sn.turatad Carbons in CTPB

°' '""

66

---- -----~ta ~~- ~

Cf)

-~=====p:: - ; ~

i

0 \i"\ ......

. ('"'\ ......

co 0. E:-< (_)

s::: ·r-l ti) +~ •r-l § _,_ -.-1

Cl) ~

~-c:::::: 0

s::: 0

•r-l b.J (!)

:::> 0 p:: ~ (""\

E:-< .-1 s::: 0 .n s.. > ro u

"'d Cl +l C\i s..

~ .E ro U'.l s:::

:::>

• ..:;t-.-1

Q) $-. ::s tJ)

·r-l µ.,

68

1 ~ ~ 0 E--1

~

J :J?

0 0 .....

0 \,("\ .....

If'\ ..... ~J r... ~

·r-1 r:r...

E

$ B

c N I F,G

A

50 40 30 20 ppm

Figura 16. C'.1.:rbcn-13 S·pctr3.l Rc:?;ion of Sat11rated Carbons in PBAA

71

--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-, G ci.. p.

(/')

::::> . E-<

~

< ('.. N ..-4

0 (""\ ..-4

..::T '-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

< ~: trl 0...

i:: •rl

Cll +) •rl i::

::::> 4 . ..-I

c.-i 0

r: 0 ·rl bL Cv p::

c 0

..0 :.... ,:; (.)

'd CJ

+) .:;j ;:... ::.J +' ("' ., (j) ~

::::>

. CJ ..-I

f..' ;.., :::s !:..'.)

•rl µ..

SUrmA ... ~Y

The compositions of the polymers are found to be:

Polymers Vinylic-1,2 Cis-1,4 Tra.ns-1,4 Units, % Units, % Units, %

liTPB 22.0 25.4 .52.6 CTPB 24.1 23.9 .52.0 PBA.L.Y.· 13 • .5 24.9 61.6

*Percentage composition of PBAA is nomalized to an assur.~~d 100/b pu:rity.

The distrl bution of the thr-:::e strLl.cturo..l u.-::'.. ts among the polyr..ors

is completely r;:! .. ndom, and ca.~ bo describ:d 1-y B~r~oulian statistics.

Branching in tl:esa :polymers is low ( cstiraated to b:; less than Jp).

Two types of hydxcxyl-bearing end caroons arc observed in HI'PB.

72

PARI' II. NITROI'OLUENES

INTTI.ODUCrION

The ca:cbon-13 spectra of all six ison:eric D:-IT' s (dinitro-

toluenes) and four of the possible six isomeric TNT's (trinitro-

toluenes) were obtained. Besides serving the cor.unon purpose of

qualitative a..•alysis, the cher.iical shifts of the carbon nuclei provide

other useful info:::mation. Q.uantitative analysis of a. mixture of nitre-

toluenes is possible. Ca.roo:i-13 s:U.fts of aroma.tic carbon a.tor.is a.re

kr.mm to give good co:.Tela:'.:.ions with tl:ci:;: 'i:'-electron C.en.si ties and

totr.l elect:r·on d::msi ties. This provid.c:.:s a means in testing the

successfulness of va:c-lous r.:olecul~ orbital calculations such as

DIDO and Cl.TIO. 22 In mono-substituted bznze:;.es, clos:;? :relationships

exist b~tw.Jcn the chemical shifl~s at the p::ra :posl tions a.r.d Ha.ru::.ett-

This allo~rs sane prediction to re ri:.ade, from

carb~n-13 sp3ctra.1 Cb.ta, on the relative reactivities of a fai'.ily of

substi tutcci. compounds in re<J.C"i:.ions nhcr.;) Hr..r.i.-r.;)tt-type paxamcters a:re

important. The reactivity of a co:;;p,:n:.nd ldll vary in diffcr'3.nt

solvents due to solvent-solute inter.J.ct.ions; the carbon-13 che:r.ical 24 shifts provide a ::neans of r::onitorins the subtle changes.

7J

EXPE:?,:mE!;T AL

The standard solvent employed. for the nitre-toluenes was

deute~"Ochlorof o:rm and the concentration was approxi~ately 15% weight/volu...~e. The exceptions are: (a) an approximately 5% solution of 2,3,5-T~T; (b) an approximately 15% solution of

2,3,4-TNT in deutera.ted dimethylsulfox.ide; a.--id (c) an approximately

15% solution of 2,4,5-TNT in a mixture of 80% deuterochloroform and

20% deuterated accto~e by volune.

To obtain proton-decoupled spectra, the proton-irradiation

frequency ~·r:;.,s set at about 4 ppu: downfield from TES in the proton

resonance ~cang;;, (i.e., around 99, 998, 700). A noise b3.11d width of

1 KHz on either side of the :proton-h'Tadiation frequency was chosen.

90° rf pulses (cc:.. 19 µsecs) ~1ith rep:o:tition tir:cs of 5.0

seconds were used. The nun bcr of s.::a..'1s =~quired to obtain dec~nt

signc:.1-to-noise :ratio in a proton-decoupled. sp;;;ct:i..·1un was about

20,000. The nu...71bcr of sc<:.ns req,uir:-0d in a proton-coupled spectrum

was aoout 50,000.

All chemical shifts Eentioncd a.re m.east:.red with T;·iS (tetra-

methylsilan~) as ref0renca. Positive signs indicate des!U.elding

relative to THS.

74

RJ?3UI.TS Al'ID DISCUSSION

Sp3c-'lir::>.l Asslgnmc11ts of Ni trotolu8nes

The assigned chemical shifts of the nitrotoluenes are tabulated

in Table 7. Assignn1ents were based on consid.era.tion of the chemical

shifts in proton-decoupled spectra a."ld coupling information in the

corresponding proton-coupled spectra.

Inspection of a proton-decoupled spectrum perraits easy assignment

of the methyl carbon, whose resonance is considerably shielded from

the aro;:-.c:..tic carbons. In the aror.:a-tic rcG'ion of a decoupled spectru.'l

(115 - 1!.~.5 pp:a), t~ee types of p.::o..ks of different intensities can be

o bservcd. P;;::2.ks of h:i..ghect intensities co:nc: fror.1 arowc:.tic carbon

a-toms with d.irzctly '!:x:>ndecl prc·~ons which e;ivc ther~ cor:rp~~ratively short

relaxation ti:::•.;;s. Pco.ks of intcnwd.iate intensities are G.ue to the

resonances o:? ca:cbon atoms 1;::. th c:ircctly bo:-:c:$d. f.l(}thyl 1:r.:oups. Peaks

cf lowcs·t. inte!1s::.ties are th0 r0sult of aro1:ic.tic carbon nuclei Hith

diractly ronde::l nitre g-.coups. 'l'h0so car"con nuclei in the last category

have long spin-lattice rel~ation tin0s due to the absence of proto!1s

in close proximities to provide dipole-dip~le rGlaxation. To Eake

mt.tters uo:csz, ti:lesc car con signals a.re b:::'oadened o:ring to the quadru-

pole inte:.:action ~dth dii--cctly l:onded nitrogen-14 nuclei, making them

undetectable in many c~ses.

When the proton-coupled spectra are obtained, specific assignments

of the pea!~s in the aromatic recion can ce made, based 0~1 the long

range carbon-13 - proton coupling consta.~ts which a.re shown in Table 8.

These constants a,eree v:ith those reported by Weigert and Roberts. 2.5

75

76

As an example the spectral assignment of J,4-DNT is discussed.

The proton-decoupled spect:cum of this compound is shown in Figure 19.

In Figure 20, the aromatic region is expc:..~ded to show the separa.te

signals from c2 and c5 Hhich a:ppear a.s a single signal. in Figure 19.

The three types of peaks of different intensities menticned earlier,

are c bserved. The :Jroton-coupled spectnu:i. of this con:pound is shown

in Figure 21, and Figure 22, which was 11 smoothed11 in order to improve

sioml-to-noise ratio. Assit'.;Il.i:ent of S is n0 pi"Oblern since it is the

cnly pz:a.'!t of inter.iU.~diate in-ccnsity in the decoupled spGctrum which

ro:nains as a singlet Kith inW.cation of moderate couplins with the

mcttyl p~otons in the proton-coupled s1)zctrur.. As a first ord~r

::.pp:coxiTil~:tion, signals fro::! c2 , Ci:, z.nd C,. a:cz doublets due to the .) 0

st.ronG cou:..;:.::r.gs with thzir di:;:cctly ecnded p:coto~s. c5 is coupled

·co :p:r.:i-'i;cns on c2 and c6 with cou:plin.:; cons·(.a.nts of 1 ·co 2 r~, which arG

o b;;;c:::.."Vcd. as ~, "b.:.:oad.cning ra.thc;r th:;.n s:pli·::.ti~g of the spect::al line

into distinct nult.iplets. Couplin3 of c5 Hi th a.'1.y other proto:1s are

too •rca!i:: to 1:3 obse:::..··ved. 'i'hc::..'"'Zi'o:co c5 stould app(;;::.r as a doublet with

r.o fine st:J..~..icture. As c2 is coupled r::od.era·;;.cly (JCH of 6-8 F.z) to the

p:roton attt:-ched to c6, a.nd weakly (JCH of 0-1 Hz) to the r..ethyl pro-

tons, its doublet should bo broc:.dex than tl-:.at of c5, and should shall

some fine structu....""\;;. c6 is coupled moderately to the proton attached

to c2 , end woakly to ·the Iilethyl protons as l:ell as the p:roton attached

to Cy Hence, its doublet should shoH the nost fine structure. Thus

c2 , c5, and c6 are assigr.ed. The a.ssigr~~cnts are reasonable ~hen one

considers a compound in which the methyl group is absent (i.e., ortho-

'l'l1DV..:.: 7

C~.rbon~13 Ct::m1ic:i.l Shifts of Nitrotol1:7"m8s

Cmiipou:1ds ci c2 c 1 C4 c5 c6 CHJ

132.63 i:: * 123.16 2,3-Di{T (1l}L'.Y+) (1.!~L59) 130 .l~l:. 137 .12 17.23 -'· ..j..

2,4-DllT 1ho.70 1l~9 .5l1 .. 120.19 1'.}7. il}. 126.99 131J..OS 20.63 2,5-D2il' 1)5.17 1 c:2 5r+ :>,, 0 j 125.59 122.07 -'· 1'1-9.25. 127.65 20.02 2,6~1xn· 127.60 151.56 127.59 127.75 127.59 151..56 14.74

+ ... 3A-mn 11}5. 97 125.30 1 1~3.39 137.68' 125.16 133 .51~ 21.36 3, s-rnrr 11~.2 .l16 ~.~9.~/. 11}9 .11 116.30 11~9.11 129.22 20.07

:!I: 1/J.0.16 f •• .,~ ,....._.):_< (•r,,• '(')* ('l• r.1 1 )':' 2' 3 ,4-'l'i!'l'. \.\'.-.• ;.) \.:.;;),: ... · 1 .. 0.y1 128.19 136.78 18.21 * * * ,. I ,,...., .~ .. ~. t.: 2,3,5-TllT (136.13) (F;.5.;.}~) (11~3.ot) 118.9'1- ( ..... ; :; ) 131.53 17.60

}~ "' >'.• .... 2~4, 5-T~:T''° 141.61 ( ~ l·" 29 )' 122.40 (139.?ZJ.) (14J.37) 129.56 20.56 " ,:; . 2 ,4, 6-'l'!!T 131: .• 28 151.68 122.31 11J.5. 73 122.31 151.68 15.65

* Cherdc::i.l shifts in }'.:~rcnth:Jsis .::.r0 cstir.:~t t0d cl::;mic:.l shifts, usinz the p-1.r~r.:-;ters from lin:3ar ra~~:c..;ss:icn [.!t:~'l;</cis. Th:cy ~.re no·::. ob32~·;.::d cxp'.:!ri;~2nt~clly.

:i: Solvent is cl:mt.cro.t~:d dir:3t~1,Ylsulfoxidc:.

it Solvont consi::;t::; of v.ppro:dr::'.ltcJ.y 8o;s d:::mtcrochloroforr11 ar.d 20~ d:mter~.ted acet.ono ..

+ Assir,rnr.')nts of nitro-st~bstitut-:;cI cc>r'oo!!s in ncn~sy:~.i.,;.:-tric nitrotolusnen are tentative.

-..;) -..;)

C6 C~,C5 CH'.3

Ci

c3 c - I h '~t...~ .. ,J •• .:' '-l. ,_,,.,i,. i.,,. ... ,..;.< ~.'"le •. \':-:: ~ ~ir,-,-4._..,,...~.·J, ... .r"J~~....--,.rl~l'···1r"'l 1lf ~,, f

I I

200 150

Ct~1J

·10 \ 2

CTT ,r,3

THS

11.Jl, '•' '''· ,, . , •,. "r 11,1,, l.,JJ," """'' "~' "tl·.' I~-'"·~ 1> 1.. ..J;<-.fl ~ """"''''"''""'"'-'""""""" 1•• tp1lr.,.J"'r1rnrn'''''r·111.ptr1r,: ... r ,..,,'1,rf"'r--,1 'ii •'",..-~•1 .,.,"'"t ..... r .... , '( .. .,,il >i *'r1;.,""lil' r~"~'ti.,..~.., ... ,.-,.1Y1"1j""'1~ 1 _L__ J I I I I I

100 50 0 ppm

Fii;ure 19. C:->.rbon-13 ~~; 2 S-c~ ctrm'l of 3, 4-Dini trotol u~ne

--.J CP

~-~~~~~~~~~~~~~~~-~~~~~~~~~~~~~~~~~-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

CH) c6

"O !': 2 c2 I' c5

c1

c3 Ci~ Jl j . " ~~1.•u,-\...

'rli'.,;,,.,.,.~rrf'"'V\~~· .. ~,n\•~·'t!~?·~(I ••r-,,\'#",rNftN'/~rr ... ~'~"'~.l!'r'·fi-~Vr- ,:IJW.f-M•·~···~~~Mr~., -~

I -----------11-1-5 11.:-0 135 130 125 ppm

Figu:r.:: 20. Carbon-13 !ll-'.:?. Spctrum of Aro~.:·~tic c~~:·bo~ls in J,l.t·-Dinitrotoluene

'"" '°

CHJ

l.:02

"'0 j, 2

doublets of

c II C2&C5

it CJ C4 IJ d~~b~~t ~ I I

1f 1\q I 1~\ 11i·l1. t1 ,,11 ~11,, .. J l ! ~I. J~ I 1J ~I ,1 ~ll t I 'lkl\.1,\i'I'' .'«',,,, ,/ ,J 11 ,. "/ ,,1h,1 l1~ I 11111,l,11 f.·~ J , .. 111·'111.11'.•.f i:l.11 11).1:1l 1\l"l'~1l \1H~ l1~N ~11.~l::~l~}·~ r jl (\'i1if 'Ii', ftlj i{ ·11,J ~di 11;'{:!; fi/d~ 11~11;i-1·~(\il :1(

1i H·1''lf'j,)1'J'lf'j' 111~(r1 11 Vr1' I

.) ll('l /.1 'l. I ~ I-·----

150 145 140 135 130 125

,1h IJ)\µJJ11 ~,J\~!}J ! r ( .;,rn1r!I' drl'

120 pp;n

Figure 21. c~.rbon-13 NiIH Spct:run of Aro;-:-.:i.tic Carbons in 3,1~-Dinitrotolu-.me (Proton-coupled)

CP 0

CH3

N02

c 1 CJ c4

)/~ ~ ;VI, .

~1 ij~,·1,1r\~1~\~~~,r~J11 145 14-0

doublet of c6

~

l. !..J "' ~.rf11~ iru1,1111,v:') ~'t ,,,, ~ •" u11 I jl 135 130

doublets of

c2 & c5

~N~\~k~~1~~~ 125

!)J 120 ppm

Firure 22. C~rbon-13 NViR Spectrum of Arorr~::.tfo Co.:rbons in 3.11--Dinitrutolucne (Proton-coupled)

():) ....

82

TABLE 8 Coupling Constn.nts between Carbon-13 ~!uclei and

Protons in Substituted Benzenes

Conditions Coupling Constants, Hz -x-

~ 2 JCH: 7 - 10

~-©("J 3 I JCH: . - 2 ...

* H

© 1 3cH: 150 - 170

* ©f" 2 3CH 1 - 2

©lH' JJ . CH" 6 - 8

lQJ 4 0 - 1 3cH 0 ··* h

All other couplings not listed are assumed to be zero.

83

dinitrooonzene). The chemical shifts of c2 and c5 would be identical

due to symmetry. The effect of a non-directly bonded methyl group

is s.11cll. So the resonances of c2 and c5 of 3,4-DNT a.re expected to

re very close. Assignments of c3 and c4 a.re not too certain. c3 couples moderately with only one proton (the p~"Oton attached to c5)

while c4 ccuples moderately with protons attached to c2 and c6• So

the peaJ>: from c4 shoulCi. be broader.

U'tili t.y in ~'i:l:ct.ur'2: /,J~ 22.;vs:l s

Insp<3ction of 'l'able 7 shows that the c!1emical shifts of the

ncthyl carb-.Jns occur over a ra.."'lge of app~oLmately 7 ppm, and that

the ch~;::ica.l shifts of tho aromatic car1:ons occur over a range of

approximately 35 ppm. This permits the qualitative identification

of the individual c0r:1ponents in a mixture of nitrotoluenes. Since

tl1e qualitxl:.ive analysis of nit:rotolucncs by proton :nagnetic resonance

sp3c-'c.~"Oscopy is inpossible C:;)CO..Use of the n2.rrow o. 2 ppra ra.'1.ge in

which methyl proton re:::onances ara found, c.nd the narrow 1.5 pp.11

z-anga in l:hich a....-omatic proton resonances arc found, superiority of

Czi.rbon-13 !n-.!R as a qualitative tool is clearly demonstrated.

As th~ cor::cspondin.:; p::otonated co.rl:on ato:::s in the niti"Otoluenes

should have ver.J similar rela..~ation times and nuclear Overhauser effects,

~hey should have almost i~cntical spectral response facto~s. Hence

the quantitative analysis of nitrotoluenes is possible.

84

Rcsression Analysis on Spectral Data. of Nitrotoluenes

The che&ical shifts of the aromatic ca.roons and methyl carbons

of the nitrotoluenes were, separatively, correlated with some para-

meters by the use of multiple linear regression analysis, which is a

lea.st squ~e fit of the chemical shifts in more than one variables. 26

The purpose of this regression analysis was two-fold. First, chemical

shifts of substituted benzenes, whose substituents are nitre and

r.1ethyl g-.roups, cc:..n be estimated. Second, the spectral assignments

me.de previously could ba checked with the results from the regression

analysis. It is expected that incorrect a.ssiGn.~ents lead to degraded

results.

The chemical shifts of the a:romatic cc.rl.""Ons are fitted v:ith 19

pa..i..-a.r~eters. The rcslllt is tabulated in Table 9. The coefficient of

dc-~e:rr::inc.tio:n (square of correlation coefficient, or r 2) is a high

0.994, which is quite close to the perfect 1,000. Soille of these

pa::::i.meters (those marked with m1 asce:c-lk in Table 9) are ::.:'ound to re insignificant by re{!;l:'0ss:ion analysis. Their ma.::,nitudes were less than

O.J ppn, with standard er.cars of 0.5 to Q.8 ppm when included in the

regression anc:..lysis. As a result, their ma6Ilitudes ucre taken as

zero, and. they were excluded in the linear regression analysis. The

exclusion of these paroJ1~ctc:rs lead to a surprising result-tl:e

estimated standard error of a calculation using these paranters

dropped from 0,94 ppm to 0.87 ppm, while the coefficient of deter-

~.ination remain constant. The intercept from this analysis was

8.5

128.47 which is virtually identical to the reported 128 • .5 ppm chemical

shift of the carbon atoms in the parent unsubstituted benzene.

The pa.ra.~ete:rs used are semi-empirical; exact explanation of

their theoretical origins is difficult. The first eight para.meters

seem to account for the inductive effect of a methyl and a nitre

group at various positions. The next eight para;.:cters were introduced

to allow for possible steric interactions of methyl- nitre groups

with an adjacent suostitut.ent. (Since the stcric interaction of a

:U.tro grvup -::ith a methyl g;roup is eX})ected to be diffe:cent froi:l its

interaction with another nitro croup, the eiGht pare.meters just

mentioned were 0~1c0 separated into t..,elve parz.n:eters. It was, however,

su:cprising to find cut that the correlation Ki th this separation was

exo.ctly identical to -~hat without.) The last three pa:::roneters were

introduced to provide for some sort of resonance effect. Notice that

t:1c int.e::c<J.ctions of two group::; o:rt.ho to each other a.re missing in this

set of pa.r.'.l.!:!eters. The reason for this is thc..t they have already been

includ.:.:!d by the para.!lcters, 11 ortho C~" ar.d/or "ortho N0211

• R~sonance

interaction between tuo groups :i1et2. to each other is of little impor-

t3..11ce, sc this para.i:eter was not included.

As the use of r.inctcen para.~eters seems inconvenient, some of

the p~"'<l.l-:i.cters were dropped to see how r:mch the r3Sul t would degrade.

The corr0lation of the chemical shifts of the aromatic carbons with

the fir::>t eight pa:ra..~eters are shown on Table 10. The coefficient

of detei"!ilination dropped from O. 994 to o. 977, the estimated standard.

er~or of a calculation increased from 0.87 to 1.59 pp~, and the inter-

86

cept is now 128. 72 ppm. If the first sixteen of the nineteen para.-

r.ieters were used, coefficient of determination of 0.991 a.nd estimated

standard error of 1. 05 ppm would be o bt.ained. The intercept is now

128.22 ppm. The results of trd.s analysis is tabulated in Table 11.

As a check for the correctness of spectral assignment, the

assignments of c3 and c4 of J ,4-D1'T were reversed. The coefficient

cf dctenrdnation, and the estimated standard error degraded signifi-

c~ntly, sho~dng that they wcra not misassigned. When misassigned,

the ~esidua1 (obserrcd chemical shift - calculated chemical shift)

is positive for one carbon atom and negative for the other. Inspection

sl:owed thd their raversa.l b::i.ck to the original (correct) assignment

~rould inprove tha r0sult. No assign.'lent of the spectral data was

obse:;:v3d to kncfit f::om s»ritching. This supports further that all

the assign.:::.:mts cixe co::crect.

Reg-.cession analysis was perfomcd on the chc:nical shift of the

metbyl carbons in nitrotoluenes usinc; six pa.:::-a.":":etcrs. The results

are tabulated in Table 12. The coefficient of dcterrnin~tion is a good

0.991 while the estimated standard error of a calculation is a ],ow

0.34 ppm. The intercept. is 20.96 ppm which is very close to the

21.l ppm chemical shift of methyl carbon in the parent toluene.

These six p3Xarneters are condensed fron the nineteen para.meters

used previously on the analysis of the aromatic carbon chemical

shifts. Hhen all nineteen parameters were used, some colur.ms in the

dz.ta matrix were all zeros, a.nd some were identical. The exclusion

of these parameters with all-zero columns or repeated redundant

*

+

87

TABLE 9

Carbon-1) Chemical Shift Parameters of !'~ethyl and Nitro Groups for Aromatic Carbons in Substituted Benzenes

+ Parameters

directly bonded CH3 ort:ho cH3 meta Ct1

"3 po.:~a CH"

.)

directly bonded N02 ortho NO 2 recta N02

\TO p~:-a .\ 2 cro~·Tding of direct CH 3 cro~rding of ortho CR..,

..)

crc-:·7C.ing of r.:eta CH3 crowJ.ing of D~r:l CHJ

cr017ding of dir0ct uo ~" 2

crowding of ortho N02 c:rm:ding of n:cta NO 2 crowding of p;:ira '10 ,, 2

direct CH) and parc:t N02

direct '-TO " 2 and pc:ira CH) direct N0

2 and p:J.ra 'TQ ., 2

Chemical Shift, ppm

10.02 :t 0.59 * 0 * 0

-2.65 + 0.50

19.61 + 0.49 -4.46 :t 0.23 1.41 :: 0.33 5.70 ± 0.57

-1.33 ::!:: o.44 L 78 ::!:: o.43 * 0

-1.23 :!: 0.51

-2.03 :t o.64 * 0

0.61 :t 0.32 -2.30 :t o.45

2.18 :t 0.69 * 0

-1.62 .:t 0.79

Par.:i.rr.::it·:::rs found to be insignificant by linear rer;ression 2.nc~lj•sis. When included in the regression analysis, their m.?.gnitudes were less than 0.3 ppm. with standard errors of 0.5 to o.8 ppm.

Parar::etcrs are semi-empirical; their theoretical origins may not b~ wh.3.t their names imply.

*

88

TABLE 10

Simplified Carbon-13 Chemical Shift Parameters of Xethyl and Nitro Groups for Aromatic Carbons in Substituted Benzenes

+ Parameters

directly bonded CH3 ortho cH3 rr:;;ta CH'.3 p;;.ra CH'.3

directly bonded N02 01~tho N0

2 m3ta ~o2 para N02

Chemical Shift, ppm

10.23 ± 0.57 * 0 * 0

-3.32 ± 0.61

18.96 ± 0.59 -4.74 ± 0.35 1. 79 ± 0.33 4.37 ± 0.50

Pc:;.r<J.n:8t::!r:::: .found to b'.2! im~ignificant by lin8ar regression ar.,-:.lysis. 1·n1cn included in thz r8g1~css:!.on c..n::.lysis, their rr .. ;.gnituG.o were less than 0.3 ppm, with st<i.ndard errors of 0.5 to 0.8 ppm.

+ Pa1·ar:eters are semi-empirical; their theoretical origins may not be what their nan:es imply.

*

89

TABLE 11

Simplified Carbon-13 Chemical Shift Parameters of !~ethyl and ~ritro Groups for Aro:m!':ltic Carbons in Substituted Benzenes

+ Parameters

directly bonded CH3

ortho C:-13 rcata CH

3 para CHJ

directly bond~d ~o2 .,_, FO ort. •. o ~ 2

r.:eta N02 pa.ra. N02 cro~•din[; of direct CH

3 crowd ins of ortho CH

3 crmrdine of TI::)t3. CH3 crc::·;di11g of p?.r;::. CH)

cro:-1ding of direct N02 cro-:·idinz of ortho NO 2 crowding of rr:~t~ N02 crm1ding oi' par~ N02

Che~ical Shift, ppm

11.07 + 0.60 * 0 * 0

-2.38 + 0.59

19.43 + 0.55 -4.46 + 0.27 1.46 + 0.39 6.32 + 0.53

-1.32 + 0.52

1.55 + 0.51 * 0

• t::. / -.1. ·~o + 0.60

-1.90 + 0.76 * 0

o.88 + 0.37 -2.72 + o.49

Parc::.;-;;sters four.d to b:;; insignificant by linoar regression <>.nalysis. ':.''r.cn inclt~dcd in the r8gression analysis, their :i::r::nitudc were less than 0.3 pp:n, with st<mdard errors of 0.5 to 0.8 ppm.

+ ... . . . 1 th . tl-. t• 1 .. FD.rmr.e .,ers are sem1-emp1r1ca ; eir i•core icv. origins m3..y not te 'trhn. t their nan:es imply.

90

TABLE 12 Carbon-13 Chemical Shift Parameters of Nitro

Groups on Hethyl Group in N'itrotolucnes

Parameters

ortho N02 n:eta NO 2 p<J.ra N0

2

crowding of ortho ~ro2 cromiing of n:eta N02 crowding of para N02

Chemical Shift, ppm

-5.29 ± 0.34 -0.Jl ± 0.20 0.60 ± O.J4

4.51 ± 0.52 -2.J2 ± 0.31

2.40 ± 0.52

91

para.meters lead to the six parameters used here. The first three

para.meters seem to originate fron the substitutent inductive effect.

The last three parameters appear to account for the steric crowding

effects. Notice that the parameter, "ortho N0211 has a built-in steric

crowding effect of the ortho nitre group already; that is, the steric

crowding of ni tro group at c2 in 2, 3-DNI' must ba counted once but

not twice when using the parameter, "conrding of ortho N0211 •

Sv.iT'.mary:

Carbon-13 chemical shifts cf nitrotoluenes are tabulated in

Table 7.

Chemical shift para.meters of methyl and ni tro groups on the

chemical shifts of aromatic and nethyl car1:ons in nitrotoluenes are

tabulated on Table 9 and Table 12, respectively.

PART III. HISCELLANEOUS CONl?OUNDS

rwrRODUCI'ION

The carbon-13 chemical shifts of some miscellaneous propellant

ingredients are given in this section. In order to have some

familiarity with them, a brief description of their functions is

given. 27,28,29

As nitroglycerine is highly nitrated, it is overoxidized during

combustion. On the other hand nitrocellulose, by itself, is under-

oxidized during combustion. The ideal stoichiometric ratio is 8.57

parts of nitroglycerine to 1.00 part of nitrocellulose. However,

nitroglycerine will not gel in nitrocellulose in amounts in excess

of 43 • .5% by weight. In order to have safe handling and long-term

stability, reduction of nitroglycerine down to 25% by weight is

common. One way to improve the performai.ice is the use of other

nitre- (-no2) or nitrato (-ON02) compounds, such as dinitrotoluenes,

trinitrotoluenes, and aliphatic nitrate esters, which are usually

p::epa:ced by the coi."Tesponding glycols with nitric acid in the pre-

senco of sulfuric acid. They are all sensitive to shock to some

extent, nitroglycerine being the most sensitive. Plasticizers, which

are the sam0 typ~ used in composite propellants, are used to strengthen

the ru.bbs:ry matrix.

Nitrocellulose decomposes slowly, at room temperature, with

evolution of nitrogen dioxide, the accumulation of which to a critical

amount leads to an extremely-violent autocatalytic explosive reaction.

Nitroglycerine samples begin to discolor at 1J5°C; explosion occurs

92

93

at 218°0. The reaction is similar to that of nitrocellulose. It

has been found that weakly basic aromatic amines can stabilize the

propellant by absorbing the evolved nitrogen dioxide. Some of the

comrr.on stabilizers are N-methyl-p-nitroaniline, 2-nitrodiphenylruaine

and methyl centralite (sym-dimethyl-diphenyl-urea).

In a coraposite propellant, polybutadienes are cured with diiso-

cyanates, and cross-linking reagents, such as trimethylol propane to

form an elastor.ieric matrix which contains, basically, an oxidizer like

arr..monium perchlo:cate, and a metallic fuel like powdered aluminum.

Besides baing a source of fuel in the propellant, the matrix must

bind together the discrete oxidizer and metallic fuel particles to

form a tough rub'bei.-y mass capable of Hithsta.'1ding severe thermal and

mechanical stres~. It must also be resistant to deterioration during

storage. Tha rubbo:cy mass formed by polybutadienes and curing

agents alone cannot fulfill the require~ents; so plasticizers, such

as various phthalates, adipates and sec:i.cates, are added. Hyd..."""ides

of boron were once included as high-perforilla.'1ce additives because of

their high heats of combustion. However, they are extremely poisonous,

and now they a.re replaced by various carb::>ranes which are also burn-

rate modifiers. Antioxidants, such as 2,2'-methylene-bis(4-raethyl-6-

butyl-phenol), are necessary in the prevention of oxidative deteriora-

tion in long-term storage.

EXPERII1ENI' AL

The solvent for most compounds was deuterochloroform. Deuterated

dimethylsulfoxide was used for compounds with low solubilities in

deuterochloroform. The concentrations of these compounds were as

high as solubilities allowed in order to obtain maximum signal-to-

noise ratio in minimum time. Since a deuterated solvent concentration

of at least 1C% was necessary for stable long-term signal averaging,

the concentrations of liquid samples could not exceed 90% by volume.

Exceptions were the approximately 15% weight/volume concentrations of

the aliphatic nit:rate esters.

Char.1ica.l shifts are referenced to UIS. Positive signs denote

downfield direction.

More details about the spectrometer are included in the Appendix.

RESULTS AND DISCUSSION

Tables 13 through 16 show the caxton-13 chemical shifts for

aliphatic nitrates, cartoranes, plasticizers, and stabilizers,

respectively. Spectral assignments of the peaks were made from

proton carton-13 cross-correlations and/or coupling information in

proton coupled spectra.

Good separation of the chemical shifts make qualitative analysis

of the compounds in the four categories possible. With the addition

of a.n approprlate pa..i..--a...~agnetic r~laxation reagent, such as tris-

(~cetyl~cetonato)chromiur.i(III), which will almost equalize the

ci:l.fferent Overhauser effects of the different carton nuclei, quanti-

tative analysis is possible by using a sufficiently long pulse

repztition rate. 30

9.5

96

TABLE lJ

Carbon-13 Chemical Shifts of Aliphatic Nitrate Esters

Ccmoou."ld.S Chemical Shifts, ppm

Nitroglycerine O:G)

2 1 yH-(CH2-0N02)2 ON02

Propylene glycol dinitrate (FGDN) 3 2 1 CH3-7E-CH2-0t-.:02

oxo2

1,2,4-butanetriol trinitrate (3TTH)

4 3 2 1 rH2-CH2-yH-CH2-0l'J02 0~02 ON02

Triii'lsthylol ethane trinitrate (TEETN) 3 2 1 CH;-C-(CH2-0N02)3

Diethyleno-glycol dinitrate (DEGDN) 2 1

0-( CH2-CH2-mm2) 2

Triethylene-elycol dinitrate (TEGDN) 3 2 1

(CH2-0-CH2-cH2-0N02)2

~ 1 = 68.19 b2 = 74.81

~1 = 71.99 b2 = 76.07 ~3 = 1.5.03

bi = 67.89 ~2 = 70.86 ~3 = 27.24 ~4 == 53.57

?>1 = 72.81 ~2 = 38.53 7'3 = 17 .17

~. = 72.03 J,

?,2 = 67.41

~1 = 72.20 ... ~2 = 67.28 ~3 = 70.80

97

TABLE 14 Carbon-13 Chemical Shifts of Some Carboranes

Corr.pounds Chemical Shifts, ppm

n-Hexylcarborane 8 7 6 5 4 3 2 1 CH3-cH2-CH2-cH2-cH2-cH2-C~~-H

B10H10

Carborunylmethylpropionate 6 5 4 3 2 1 CH3-cH2-w-O-CH2-C\_6jC-H

O "B10H10

Carboranylrnethylethylsulfide 5 4 3 2 1 CH3-cH2-S-CH2-C. O/C-H

'\ ' B10H10

Carboranylmethylpropylsulfide 6 5 4 3 2 1 CH3-cH2-CH2-S-CH2-c\0;c-H

310H10

~- = 76.08 J.

~4 = 31.67

~ = 22.81

~1 = 73.29

~4 = 173.2

?;. = 75.11 .I.

~4 = 28.76

~4 = 36.50

~2 = 61.40

b5 = 29.61

~8 = 14.32

~2 = 60.55

~5 = 28.28

~2 = 59.82

~5 = 14.68

~2 = 59.60

~5 = 22. 76

~3 = 38.47

~6 = 29.00

~6 = 9.95

~ = 38.93

~6 = 13.25

98

TABLE 15

Carbon-13 Chemical Shifts of Some Plasticizers

Com·ooundS Chemical Shifts, ppm

i'·:cthyl se baca te

f e d c b a -(CH2-cH2-cH2-cH2-~-0-CH3 ) 2

0

>!< Assignments may be reversed.

~a = 14.14

~d = 30.49

$g = 23.87

b· =132.60 J

~a = 51.J3

~d = 25.03

~b = 23.09

Se = 38.86

.sh = 11.01

~k =128.84 *

~ = 23.09

be = 38.89

-\i = 11.04

;;j = 34.01

Sb =174.07

~e = 29.21

lia..= 20.65 ~<-= 20.84

~r:i =170.06 fi.e. = 62.28

~c = 29.03

~ f = 67.98

~- =167.63 l.

bi. =130.93 *

& = 29.06 c

.sr = 66.68 /

~. =173.31 l.

&k = 24.57

~ = 34 10 c •

~~ = 29.21 ...

~c. =170.45

~.f = 69.10

99

TABLE 16

Carbon-13 Chemical Shifts of Some Stabilizers in Double-base Propellants

Comoounds

Nethyl centralite ()

CH - 111r - Jt©-, -. c'\, . ) ' f "?- "3 © o: ~

* N-Zzthyl-p-nitroo.niline

.J,.

2-Ni trodiphe:nylamine "I·

* In DNSO-d6 .1.

Chemical Shifts, ppm

ba = 39.28 ~ =145.55

~d =128.56 L~ =124.77

.l) a = 29.21 ~b =155.35

hd =126.26 ~e =1)5.75

.Sc =125.63

s ... =161.0 ·r

~c :::100.45

116.03, 117.46, 124.38, 125.65,

126.65, 129.71, 135.63

+No assignments were made; shifts reported are for protonated carbons.

BIBLIOGRAPHY

1. R. s. Silas, J. Yates, and V. Thorton, Anal. Chem., ,2!, 529 (1959).

2. J. L. Binder, Polymer Sci., Al, 47 (1963).

3. R. R. Hampton, Anal. Chem.,~' 923 (1949).

4. J. L. Binder, A.~al. Chem., 26, 1877 (19.54).

5. W. S. Richardson, J. Polymer Sci., U, 229 (19.54).

6. M. W. Duch and D. 11. Grant, Marconolecules, .:2_, 175 (1970).

7. V. D. Hochel, J. Polymer Sci. (Part A-1), 10, 1009 (1972).

8. A. D. H. Clague, J. A. M. van Broekh.Jven, and J. W. de Haan, J. Polymer Sci. (Polymer Letters Edition), 11, 199 (1973).

9. D. I•i. Grant andE. G. Paul, J. J..m. Chem. Soc., 86, 2984 (1964).

10. J. Fw."'U!mwa, E. Kobayshi, N. Katsuki, and T. Kawagoe, Hakromol. c:1cr.i •• 175, 237 (1974).

11. F. Cor.ti, A. S0gre, P. Pini, and L. Porri, Polymer., 1,2, 5 (1974).

12. Y. Alaki, T. Yoshi.noto, r1. Imana:ri, and M. Takeuchi, Kobunshi Kagaku, .§_, 397 (1972).

13. J. Fur.iY.rn.~·ra, E. Kobayashi, .:..nd T. Kawagoe, Polym. J., _2, 231, 242 (1973).

14. J. H. Thoraa.ssin, E. Walckiers, R. \'larin, and P. Teyssie, J. Poly~. Sci. (Polymer Letters Edition), 11, 229 (1973).

15. A. D. H. Cl.:~gue, J. A. M. van Broekhoven, and L. P. Blaauw, rfacro~.:>lecules' z., 348 ( 1974).

16. L. P. Lindeman and J. W. Adams, Anal. Chem., 43, 1245 (1971).

17. D. E. D:.rman, M. Jautelat, and J. D. Roberts, J. Org. Chem., 36, '2:157 (1971).

18. H. Y. Chen, Anal. Chem., J!±, 1135 (1962).

100

19.

20.

21.

22.

23.

24.

2.5.

26.

27.

28.

29.

30.

101

E. J. Hart and A. W. Meyer, J. Amer. Chem. Soc., Zl• 1980 (1949).

F. E. Naylor, H. L. Hsiel, and J. C. Randall, r""cromolecules, 2_, 487 (1970).

J. D. Roberts, F. J. Weigert, J. I. Kroschwitz, and H. J. Reich, J. Amer. Chem. Soc.,~. 1338 (1970).

G. L. Nelson, G. c. Levy, and J. D. Cargioli, J. Am. Chem. Soc., 2!:!:. 3089 (1972).

H. Spicsecke and W. G. Schneider, J. Chem. Phys., 35, 731 (1961).

G. C. Levi!, G. L. Nelson, and J. D. Cargioli, Chem. Commun., .506 (1971).

F. J. Ucigert and J. D. Roberts, J. Am. Chem. Soc., §2., 2967 (1967).

D. 1. Harnett, "Int:roduc·~ion to St<::.tistica.l Nethods," Addison-Wc~ley PublisM.ng Conpany, Ma.ssachuzctts, 1970, Chapters 9 and 10.

S. F. Sa.rncr, "Propellant Chemistri;, 11 Reinhold Publishing Co::..-po:i.13.tion, New York, 1966.

N. Shor.i:- and A. J. Zaehringer, 11 Solid Rocket Technology, 11

John Hiley a."ld Sons, Inc. , Nau York, 1967.

J. W. Ecrrick and Eric Burgess, "Rocket Encyclopedia Illustrated," Aero Publishers, Inc., California, 19.59.

H. C. Dorn and D. L. Wooton, Anal. Chem., 11-8, 2146 (1976).

APPENDIX

(ESSENI'IALS OF THE SPECTROMErER)

A Jeolco PS-100 magnetic resonance spectrometer was used. In

the earlier part of the research, the spectrometer was interfaced

by means of a Texas Instruments Silent 700 ASR keyboard-cassette to

a Jeolco JEC-980A computer. The computer had a ffiereory capacity of

12 K words, of which 4 K words were used for Fr computer program,

leaving a maximum of 8 K words for data acquisition. The word-length

of the computer was 16 bits of which the four least significant bits

were normally required for presentation of noise. Thus the theoretical

ffiaximum dynamic range of the system should be 212 (i.e., 4096). How-

ever, the experimental value was around 250 (poss!.bly due to trunca-

tion en."'Or of the computer program). 'This means that the system would

never detect signals weaker than 1/250 of the strongest signal. Maxi-

mum signal-to-noise :ratio was estimated to be 80 for a neat sample of

ethylbanzene under a 90° rf pulse.

In the later part of the research, the data acquisition system

was changed to a Digilab Data system which was capable of larger data

acquisition of up to 32 K words. Hith an identical word-length of

16 bits and double-precision format in data acquisition, the theore-

tical maximum dynamic range should be 228 (i.e., 2.684 x 108). This

value was not verified experimentally, but dyna..~ic range in excess

of 5000 to 1 has indeed been observed. The audio filter of the new

data system was a mere 6 db/decade compared with the 24 db/decade of

the older data system. This resulted in better phase-linearity of

102

103

spectral data at a slight expense of signal-to-noise ratio. !ad

phase-linearlity could case some spectral peaks to appear inverted

suggesting, incorrectly, that they are fold-over peaks,

The new data acquisition system had a much larger capability,

but the change of the d.ata acquisition system had very little effect

on this research because of the added capabilities were conveniences

rather than necessities as far as this research was concerned. The

following contains information that is applicable to both data

systems.

The FT program was set up in such a way that the observed

frequency should be placed at a frequency that is higher than the

most deshielded resonance signal, A down-field signal had a larger

LUT.J.erical value, For example, if the most shielded signal of a

spectrum is at 25,1L15,ooo Hz, and the rr.ost down-field signal is at

25,150,000 Hz, then the observed frequency should be no lower than

25,150,000 and the spectral width no less than 5,000 Hz. The observed

fraquency c~ be set at a frequency having a smaller numerical value

than that of the most upfield signal (say, 25,144,900 for the above

example) and have a spectrum without fold-over peaks, provided that

a large enough spectral width is used, However, the resulted spectrum

would appear to be "inverted", meaning that peaks further down-field

would appear at the right of a reference peak rather than at the left

as in the case of a more conventional 61norrr.al" spectrum.

With 4o% by volume of deuterochloroform as internal lock and

lock frequency set at 15,358,456 Hz, the carl:x:>n-13 and proton

104

resonance frequencies of TMS (tetra.methylsilane) were 2.5,144,.580 ±

10 Hz and 99,998,286 ± .5 Hz, respectively. The observed proton

resonance agreed well with the 99,998,28.5 Hz determined by departmental

analytical service personnel who used a .50-.50 mixture of chloroform and

deuterochloroform.

To determine the resonance frequencies, the following procedures

were perf o:rmed. The proton irradiation was set to a single-frequency

mode with the irradiation power set at its maximum (about 1.5 watts).

The proton-irradiation frequency was changed until the carbon-13

spectrum of the TNS solution was decoupled. Note that there would

be a range cf proton-irradiation frequencies at which the TMS spectrum

appeared decoupled. The process of varying proton-irradiation fre-

quency and reducing proton-irradiation power was repeated until a

final limit was reach, such that a proton-decoupled spectrum could

only be obtained at a single proton-irradiation frequency which

corresponded to the proton resonance frequency of n:IS. The ca.rbon-lJ

resonance frequency of Tr1S was estimated by noting how much upfield

it was from the left edge of spectrum which was the center band or

irradiation frequency. 0 A 90 pulse in the ca.rbon-lJ spectrum was found to correspond

roughly to 19 µ. S of rf pulse gating time. With brand-new vacuum

power-tubes and the instrument properly tuned, the gating time could

be as low as 1.5µ,S for a 90° pulse. As the tubes aged, the gating

time increased slightly. The spectral width covered by the rf pulse

can be estimated as one-fourth of the reciprocal of the rf gating time

105

required for a 90° pulse. Assuming 20 µ. S for a 90° pulse, the half-

power point would be more than 12.5 KHz away from the observed

frequency.

The vita has been removed from the scanned document

THE ANALYSIS OF ROCKET PROPELLANTS

BY CARBON-13 NHR

by

Michael Mei-kung Ku

(ABSTRACT)

Polybutadienes, polymerized via free radical mechanism to give an

average molecular weight of )000, were analyzed with carbon-13 'ITT·lR.

The relative abundance of the three types of structural units (cis-1,4,

trans-1,4, and vinylic-1,2 units) was quantitatively determined. The

distribution of the three structural units was found to be completely

random. Branching in the analyzed polymer was determined to be low

(estimated to be less than 3 %). In hydroxyl-terminated-polybutadiene,

two separate resonance signals from the hydroxyl-bearing end carbons

were observed.

Six iso~eric dinitrotoluenes and four isomeric trinitrotoluenes

were characterized with carbon-1) chemical shifts, which can be used

in the qualitative and quantitative analysis of mixtures of these

compounds. Multiple linear regression analysis was performed on the

chemical shifts to obtain parameters which are useful in estimating the

chemical shifts of carbon-13 nuclei of methyl- and nitro- substituted

benzenes.

Carbon-13 chemical shifts of other propellant ingredients (ali-

phatic nitrate esters, carboranes, plasticizers and stabilizers) are

reported.