Post on 02-May-2022
Scholars' Mine Scholars' Mine
Masters Theses Student Theses and Dissertations
1965
Thermal degradation of poly (methyl methacrylate) in solutions in Thermal degradation of poly (methyl methacrylate) in solutions in
a closed system a closed system
Vikram Pranjivandas Parikh
Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses
Part of the Chemical Engineering Commons
Department: Department:
Recommended Citation Recommended Citation Parikh, Vikram Pranjivandas, "Thermal degradation of poly (methyl methacrylate) in solutions in a closed system" (1965). Masters Theses. 6764. https://scholarsmine.mst.edu/masters_theses/6764
This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact scholarsmine@mst.edu.
THEJ.U;lAL DEGRADATION OF POLY (HE':eHYL 1-IETHACRYLATE)
IN SOLUr.riONS IN A CIJOSED SYSTEH
BY
VIK.Rl~H PRAHJIVALIDAS PARIKH ; ) _-/
A 115230 THESIS
submit·cecl to the faculty of the
Ui:UVERSI'.EY Ot' NISSOURI AT ROLLi\
in parJcial fulfillrt1ent of the rer.:i_uirements for the
Degree of
1'-IASTER OF SCIENCE IN CHEHICAL ENGil.'l'EERING
Rolla, .Hissouri
by
ABSTRACT
A study has been made of tllc ·chcnJal degradation of
poly (methyl meJchacryla-te) of ·t'l:lo different molecular
\1Ciglrts, 2,303,000 and 43,000, in 1,2-dichloroet-~la:ne
in a closed system. The results indica-ted that -::he poly-
mer having a molecular weight of 2,303,000 undergoes de
gradaJcion while ·the low molecular vleigh·t polyraer 4 3, 000
undergoes reverse polymerization, and the molecular
vJeight remains cons-tant. The molecular weight of hig:1
E1olecular weight sarnples af·ter 48 hours decreased from
2,303,000 to 2,232,000 and 1,690,400 at. 50°C and a-t
98.5°C, respectively.
I.
II.
III.
TABLE OF CONTENTS
TITLE PAGE • • • • • • • • • • • • • • • • • • • 0 • • • • • • • • 0 • •
ABSTRACT
TABLE OF CONTENTS •••••o••eo•••••o••••o•og
LIST OF TABLES • • • • • • • • • • • • • • • • • • • • o e a • • o •
LIST OF FIGURES 0 0 • • • 0 • • • • • • • • • • • • • • • 0 • • • •
INTRODUCTION • • • • • • • • • • • • 0 • • • • • • • 0 • • • • • • • •
LITERATURE REVIEW e • o e • o • • o o • • o • o • • • o • • o o •
EXPERIMENTAL & • 0 • • 0 • • • 0 • 0 • • • • 0 • • • • • 0 0 • • 0 0 •
Ao
B.
c.
Purpose of Investiga·tion • • • • • • • • • • • • •
Plan of Investigation • • e • • • o • • • o • • • • o
Nethods of Procedure • o • e • • • • • • • • • • • • o
lo
2 ..
3·
4.
5·
Procedure for the Use of CannonUbbelohde Dilution Viscometer ••
Calibration of viscometer 0 •••••••
Density measurements by using pycnometer e .................. o.
Viscosity, relative visco&J;;ty.;-· -in"!'~.·· trinsic viscosity and molecular \'Ieight calculations ••• o o ...... .,
Polymer samples • • • • • • 0 • • • • • • • • • • •
ii
Page
i
ii.
v
vii
1
3
21
21
21
23
23
23
23
23
28
IV.
v.
VI.
VII.
VIII.
IX.
iii
Page
6. Solvent • • • • • • e • • • • • • • • • • • • • • • • • • • 28
7. Polymer solution preparation and method of degrada-tion • • • • • .. • • • 28
DATA AND RESULTS • 0 • • • • • • • • • 0 • 0 • • • • • • • 0 • • •
A. PHMA in 1,2-Dichloroethane at 50°C· ••• 36
B. p~,iA in 1,2-Dichloroeti!ane at 98.5°C •• 37
DISCUSSION OF RESULTS 0 e e e e e e e e G e • e • • 6 e e e e
A. Thermal Degradation of P~·1A, Molecular Weight 2,303,000 ..................... 56
B. Thermal Degradation of P~:IA, Molecular Weight 43,000 ....................... 59
c. Molecular weight of Polymer After Be-gradation •••••••••••••••••••••••• 61
LIMITATIONS AND RECOMME~~ATIONS • • • • • • • • • •
CONCLUSI ObiS e • • • • • • • o • • • • • • • • • • • • • • • • • • • • • 64
BIBLIOGRAPHY e e • • e e e G e • e e e e • 0 e • e e • e • e • e e e e
APPENDICES • • • • • • • o • • • o • o • • o • • • • • • e • • • • • • • 68
Appendix I -.Procedure for the use of the cannon-Ubbelohde Dilution Viscometer •• 68
Appendix II- calibration of Viscometer .... 71
iv
Page
Appendix III - Densi·ty ~<ieasurements by Using Pycnometer ..................... o•• 73
Appendix IV - Derivation of Viscosity Equation used in this ~e,ai·s • • • • • • • • .. • 75
X. ACKNOvVLEDGID--lENTS • • • • • • • • • • • • • • • • • • • • 0 • • • • 78
XI. VI'l'A • • 0 • • • • • • • 0 • • • • • • • • • • • • • • • • • • • • • 0 • 0 0 • 79
Table
I
II
III
IV
v
VI
VII
VIII
IX
X
XI
LIST OF TABLES
Viscometer Characteristics • • • • 0 • • • • • • • • • •
Pycnometer Characteristics • e o • • • • • • o o • • • •
Intrinsic Viscosity-Molecular Weight · Relationship at 30 °C £or PI'1HA Samples
v
Page
24
25
(original) o•••························ 29
Intrinsic Viscosity of P~1A, Molecular Weight 2,303,000 in 1,2-Dichloroethane at 30°C •••••••••e••••••••••••••••••••• 30
Intrinsic Viscosity of PMMA, Molecular Weight 43,000 in 1,2-Dichloroethane at 30 °C ~2 • • • • • • 0 • • • • • • • • • • • • • • • • • • • • • • • • • • • ,
Physical Properties of 1,2-Dichloroethane at 30°C •••••••o••••••••••••••••••••••e 34
Thermal Degradation of P~~ 1 in 1,2-Di-chloroethane at 50°C •••••••••••••••••• 38
Thermal Degradation of PI:>ll•lA 2 in 1, 2-Dichloroethane at 50°C •••••••••••••••••o 40
Thermal Degradation of PI4MA 1 in 1,2-Dichloroethane at 98.5°C •••·••••••••••&• 42
Thermal Degradation of PHMA 2 in 1,2-Dichloroetl1ane at 98.5°C •••••o•••••••••• 44
Intrinsic Viscosity of PI~lA 1 After Degradation for 4 Hours at g8.5°C ••••••• 45
vi
Table Page
XII Intrinsic Viscosity of PNNA 1 After De-grada~cion for 12 Hours at 98.5°C • • • 0 • • 47
XIII Intrinsic Viscosity of PN.MA 1 After De-gradation for 24 Hours at 98.5oc •••••• 49
XIV Intrinsic Viscosity of PMMA l After De-gradation for 48 Hours at 98 .. 5oc • • • • • • 51
XV Intrinsic Vj_scosity of PNMA 1 After De-grada-tion for 48 Hours at 50°C • • • • 0 • • • 53
XVI Molecular Weight of PMMA 1 After Thermal Degrada·tion • • • 0 0 0 • • 0 • • • • • • • • • • • • • • • • • • 55
vii
LIST OF FIGURES
Figure Page
1 Theoretical reaction curve for possible poly (methyl methacrylate) depolymeri-zation mechanism o•c••·············•••o 13
2a cannon-Ubbelohde Viscometer • • • • • • • • & • • • • • 22
2b Pycnometer • • • • • • • • • • • • • • • • • • • • • • 0 • • • • • • • • 22
3 Relationship between pycnometer readings and weight of water at 30°C ••••••••••• 26
4 Intrinsic viscosi·ty of P!v'.U,·lA. 1, Ho1. Wt. 2,303~000 •e•••••e••e••••••••••••••~•• 31
5 Intrinsic viscosity of P~~~ 2, Mol. Wt. 43,000 •••••••••••••••••••••••••••••••• 33
6 Thenual degradation of P~~ 1 in 1,2-di-chloroethane at 50°C •••••••••••••••••• 39
7 Thennal degradation of PNMA 1 and PMMA 2 in 1,2-dichloroethane at 50°C ••••••••o 41
8 Thermal degradation of P~4A 1 in 1,2-di-chloroe·t.hane at 98.5 °C • • • • • • • • • • • • • • • • 4 3
9 Intrinsic viscosity of P~~ 1, after de-gradation for 4 hours at 98o5°C, Mol. Wt. 2,303,000 ••••••••o••••••••oeo 46
10 Intrinsic viscosity of Pl·1MA 1, after de-gradation for 12 hours at 98·5°C, Mol. Wt. 2,267,000 •••••••••••••••••••• 48
viii
Figure Page
11 Intrinsic viscosity of p~,m 1, after de-grada·tion for 24 hours at 98 .. 5°C, Mol. Wt. 1,939,800 •••••••••••••o••o••• 50
12 Intrinsic viscosity of P~m~ 1, after de-grada·tion for 48 hours at 98.5°C, Mol. Wt. 1,690,400 ••••o••••••o•••••••• 52
13 Intrinsic viscosity of PNliA 1, after de-gradation for 48 hours at 50°C, Malo Wt. 2,232,000 ••o•••o••••o••o••o•• 54
1
I. INTRODUCTION
Studies on the thermal behavior of polymers, partic
ularly on their therr~al degradation, are of importance to
polymer science. Such studies help to reveal the molecular
structure, such as ti1e sequence and arrangement of re
peating units, or monomers, and side groups in the polymer
or copolymer chain., as well as the na·ture of the cross
links between chains. These studies also yield informa
tion about (a) the st.rength of the various bonds holding
together the polymer molecules, (b) the kinetics of de
polymerization, and (c) the effects of time, temperature,
pressure and o·ther variables, on the rates and products of
degradation.
Similarly, studies on the thermal degradation of
polymers are of extreme importance from a practical poin·t
of view. They not only explain the behavior of pol~ners
under conditions of high temperatures, but also help in
selecting the right kind of already existing materials for
specific uses where high temperatures are encountered.
Such.data can also suggest the design and synthesis of new
materials to meet special requirements.
2
Poly (methyl methacrylate) is of particular interest
in the study of polymer degradation because the prod.ucts
of the ther.mal degradation consist a~ost entirely of mono
mers and also because the molecular weight of residuals
can be conveniently measured. In contrast to degradation
in the bulk phase, degradation in solution can be carried
out with various concentrations of the solute. Any visco
sity effects which are operative in bulk phase degradation
can thus be largely eliminated. Secondary reactions are
minimized by working with very dilute solutions.
The purpose of this study was to investigate the
thermal behavior of poly (methyl methacrylate) in solution
in a closed system at elevated temperatures as a function
of time, to gather basic information about the mechanism
of break-down, and to find the molecular weight of polymer
after degradation assuming that the products of degradation
are essentially monomer units. The solvent chosen in this
work was 1,2-dichloroethane.
3
II. LITERATURE REVIEW
Studies of the thermal degradation of vinyl polymers
in solution have been reported by many investigators.
Primary studies have been made on degradation in the ab
sence or presence of oxygen and catalysts. Alao,theories
of oxidation processes involved have been proposed by a
number of workers.
Staudinger and coworkers (1, 2) carried out a nwnber
of experiments on the thermal degrada·tion of polystyrene
in solution. In one experimen·t they found that when poly
styrene is prepared under careful exclusion of oxygen it
is more stable thermally than when prepared in the presence
of oxygen. A sample of polystyrene, polymerized by heating
at 60°C for a period of three weeks, was pyrolyzed in nitro
gen at 0.1 rom pressure, at 290 - 320 °C, and a.t'.va~apJleric
pressure, at 310 - 350 °C. The volatile products ~vere sepa
rated by distillation into several fractions for identifi-
cation. The degradatj_on products \rJere found to consist,
in addition to the monomer, of a mi~~ture of the dirner and
·trimer.
4
In another experiment (3) polystyrene was dissolved
in various solven-ts and the solutions boiled in a carbon
dioxide atmosphere. The results sho~tled that the viscos-
i ·ties of the initial polymer solutions decreased wi ·th time
vlhere the extent of ·this decrease 'i.vas a function of temper
ature and type of solvent used.
Experiments were also carried out in order to ascer
tain whether a soJ_ution of rnonostyrene in tetralin could be
polymerized to the same average molecular weight at 200°C
as was obtained by degradation at the same temperature.
Tl1e resul·t.:s seem to indicate that an equilibrium between
polymerization and degradation does not existo
Schulz and Husemann (4) also carried out a number of
experiments on the degradation of polystyrene in solution.
Samples of a solution containing 0.5 per cent polystyrene
(molecular weight 340~000) were sealed (1) under nitrogen,
and (2) under air. These samples were heated at 132°C for
50 hours. Sample 1 showed a molecular weight of 320,000
and sample 2 showed one of 147~000. These authors assumed
that the small amount of degradation in sample 1 was due
to traces of oxygen.
5
Investigations were carried out by Jellinek and co
workers (5) on the degradation of polystyrene in solution
in high vacuum. The object of the work was to ascertain
the role which the solvent plays in the degradation pro
cess and whether the mechansim, as far as monomer for-mation
is concerned, is similar to that of the bulk phase. The
results indicated that monomer formation obeys a zero
order reaction in both cases.
More detailed experiments were carried out by Jellinek
and Turner (6). These authors investigated the thermal
degradation of polystyrene in 3 per cent by weight naphtha
lene solutions over a range of temperatures from 345 to
380°C. The percentage loss of weight as a function of
time was very similar to that found for the bulk degrada
tion in the same temperature range. The energy of activa
tion is similar to that of the bulk degradation. Appar
ently the solvent has a negligible effect on the reaction.
Chen (7) studied the photodegradation of polystyrene
in benzene solutions. The solutions were exposed to ultra
violet radiation of wavelength 2537.5 !. The intrinsic
viscosi~es decreased steadily with time of irradiation.
6
The rate and extent of degradation were found to be a
function of light intensity, as expressed in the following
equation:
where,
d{n)
dt = k :I
(n) = intrinsic viscosity
t = time in seconds
k = rate constant
I = light intensity
{1)
This relationship agrees with a random degradation process
where the mechanism does not follow a specific .law.
Cowley and Melville (8) studied the photodegradation
of poly (methyl methacrylate) exposed to ultraviolet light
of wavelength 2537 A in vacuum, and found that it degraded
rapidly to monomer at temperatures above l30°C. The re-
sults showed that once the reaction is initiated the poly-
mer chain splits off monomer units rapidly by a reverse
polymerization process until the chain is terminated by
reaction with another radical.
Mesrobian and Tobolsky (9, 10) carried out a number of
7
experiments on simultaneous polymerization and degradation
in solutions. Their experiments indicated that equilibrium
or steady state was reached between polymerization and de
polymerization. However, later reports by JIOI!ltg-cae;y,iand
Winkler (11) and by Thompson {12) showed conclusively that
equilibrium is not involved. These workers (9, 10) used
a reversible viscometer to determine the change in visco
sity. In using reversible viscometer the solution is
sealed off in the viscometer under air, other gases, or
vacuum: the viscometer is heated in a bath of the desired
temperature, and readings are taken periodically. In
another set of experiments, various solutions of mono
styrene and polystyrene in toluene were placed in a flask
and refluxed at lll°C. At definite time intervals, var
ious amounts of benzoyl peroxide were added. After same
fixed time a few milliliters of the respective solutions
were withdrawn and the relative viscosity was measured.
Apparently, the relative viscosities of all samples seemed
to converge to a steady state value. When large amounts
of benzoyl peroxide were added to the solution containing
monomer, the attainment of the steady state was retarded,
8
whereas the reverse \vas observed with polystyrene solu
tions. The steady state viscosities obtained in the visco
meter (reversible) were higher than those obtained under
reflux~ Similar experiments were also carried out with
methyl methacrylate. In this case, the convergence of
various samples to a steady state value was not apparent
as with polystyrene.
Thompson (12), and Montgomery and Winkler (11), found
that the nature of the sol vent had a marJ~ed effect on the
efficiency of degradation. Benzene and carbon tetrachloride
were more effective than toluene. However, carbon tetra
chloride seemed to be much less effective in Thompson's
experiments than in those reported by Montgomery and
Winkler. Thus, Thompson's results for solutions containing
0.5 gram of polystyrene and 0.1 gram of benzoyl peroxide
in 11 ml of solvent were as follows: initially {n) = 0.97;
after 48 hours at 100°C, the intrinsic viscosities were
0.77, Oo61, and 0.61 in toluene, benzene, and carbon tetra
chloride, re-.pectively. Hydroquinone was found to retard
degradation. From these results they concluded that the
role of the solvent may be that of a transfer agent.
9
Radicals derived from benzoyl peroxide collide with solvent
molecules thus producing solvent radicals, and these in
·turn might react \o'li th polymer molecules_, causing chain scis
sion. The efficiency of this process is expected to be a
function of the type of solvent used.
Taylor and caverhill ( 13) studied ·the thermal degrada
tion of polypropylene promoted by organic halogen compounas.
~1e results indicated that a high degree of chlorination
was necessary for proQotion of degradation. Additional
work by these 1:..rorkers ( 13) suggested ·tha·t bromine compounds
were more effective than chlorine compounds; the results
obtained with dichlorodifluoromethane suggest in turn_, that
chlorine compounds are more effective than fluorine corn
pounds.· By heating at lower temperature (259°C) it was
found that carbon te-trachloride was more effective than
chloroform. They also found that a variety of halogenated
hydrocarbons -v.rere active in reducing ·the molecular \veight
of polypropylene heated in the absence of air in the temper
ature range 240 to 280°C. In the chlorinated methanes_, the
activities rank as follows:
.. CC14 > CHCls > CH2Cl2 > CF2Cl2
10
Bamford ( 14) and co\vorkers found t!1e sarne order when ·these
compounds were used as chain transfer agents in vinyl poly
rnerization.reactions.
Harrison (15) investigated the effect of air and iron
salts on solutions of polyvinyl acetate, polystyrene, and
pol~ethyl methacrylat~. The viscosity of these solutions
decreased in the presence of air a·t a ·temperature of 60 °C.
'1"'11e viscosities of solutions of polyvinyl acetate in bis
(2-chloroethyl) ether, kept at 60°C in the presence of
0.003 per cent anhydrous ferric chloride and 1 nun Hg of
air pressure, increased "'.viJch time, and gelling ·took place.,
1~1en the same experiments were carried out in the presence
of larger amounts of air, the viscosity first decreased
before a gel was finally obtained. The general effect was
·that oxygen shows a degrading ac-tion, whereas iron salts
lead to cross-linking.
Mechanisms of degradation of poly (methyl me·thacryla·:.:e)
have been proposed by many investigators. Kuhn's (16)
interpretation was based on the random breaking theory that
linear polymers degrade entirely by random scissions of c-c
bonds in chains.
11
Simha (17) suggested that the mechanism of for.mation
of monomers is due to stepwise breaking away of monomers
at chain ends. Later Blatz and Tobolsky (18) considered
that depolymerization takes place by a stepwise breaking
off of monomers, and is a reverse process of addition
polymerization. In fact, this is exactly the same
mechanism as suggested by S~a.
An extensive investigation of the ther.mal degradation
of poly (methyl methacrylate) was studied by Grassie and
his associates (19, 20). Since the volatile products con
sist of the monomer which has a high vapor pressure at
roam temperature, the pressure method was used in measuring
the rates. According to Grassie, the theory of random
scissions of chain bonds proposed by Kuhn (16) to explain
the hydrolytic degradation of high polymers is insufficient
to explain the thermal degradation of vinyl polymers, par
ticularly in cases where the pyrolyzate contains a large
amount of monomer. They considered the various possible
models of molecular weight change due to depolymerization
or polymerization. It was postulated that appreciable
amounts of monomer appear in a random scission process in
12
large molecules \<vhere the average molecular weight of re-
sidual is reduced to a small fraction of its initial value.
Thj_s behavior is represented by line AD in Figure 1.
Another sugges-tion was that ·tile bonds joining ·the end
units to the res-t o£ the chain micrht. be particularl v vulncr-__, ~
able and thus e:,clusively become broken.. Such a process_,
known as stepvlise depolymerization, v:ould result in a oe-
crease in molecula.r \'leight directly proportional ·to the
amount of monomer produced. This behavior is represen:ted
by line AC in Figure 1.
A third possible depolymerization mechanism is the
exact reverse o£ polj(meriza-tion. Initiation would consist
of chain scission resulting in the production of radicals.
This would then rapidly lose monomer uni·ts until they had
completely disintegra-'ced. If these degrading radicals had
life ·times of the order of those of the growing radicals in
polymerizing systems (approximately 10-3 - 10 sees) virtu-
ally all the monomer units would exis-'c a.t any instant as
free monomer or unchanged polymer. No large change in the
molecular weight of the residue \vould therefore be expected
13
A B 100
n m ~ -~ ~ -~ ~ 0 ~ 0
• ~ ~
• n 0 ~
~ ~ m u ~ m ~
0'~------------------------------------------------------~ c 0 100 Percent Degradation to Monomer
Figure 1. Theoretical reaction curve for possible poly (methyl methacrylate) depolymerization mechanism~ {20)
14
throughout the '¥Thole course of reac·i:.ion. This mechanisra
is represented by line AB in Figure 1.
Grassie and Nel ville ( 20) s-tudied Jche effect of pyro
lysis on the molecular weight of bulk poly (methyl
methacrylate) san1ples. The results ob·i:.ained in these e.:;:
periments showed that for the pol:;{:raer of molecular v-1eig~1t
44,300, the molecular weight of the residue remains con
stant through 65 per cent degrada.·tion. The mechanism of
this reaction con1c1 conceivably be u. :.:cverse pol~;merization.
This series of e:::periments, however, gives no indication
how the chain breaks initially; v1~1e·t:i.~er, for example, eacJ:1
bond in the chain has the same possibility of initial rup
ture or whether the ends of the chains are the v-.reak points.
As the molecular v-1eight of the ini·tial polymer is raised,
the mechanism ceases to be stric·tly reverse polymerization.
In the later s·tages of the reaction the molecular weig"i1t
falls. The degradat:ion of polymer of molecular Y.leigh·t
94,000 was a reverse polymerization up to about 30 per cen·t
degradation. The molecular weight of t'l1e 179,000 pol~nner
falls after about 10 ·to 15 per cent degradation while ·the
molecular weight of the 725,000 pol~~er appears to suffer
~n immediate fall.
15
Har-t (21) also studied the chan9e of molecular ~Teigll·l:
of the residue "Vli th respect to the extent of degradation,
using two grades of poly (methyl methacrylate). Polymer A
\:las prepared in ·tl1e presence of 0. 6 per cent. benzoyl per
o:-cide and had an average molecular \'leigh·t of 150,000.
Polymer B was prepared by placing a pure-grade monomer
wi-thout promoters in an evacuated tube and keeping the tube
at -25 ·to -35 °C. r-c had an average molecular weight of
5,100, 000 as de-i:.erm.ined by ·the light-sca-ttering method.
The results showed that the higher the molecular ·t;~eigh-'c -'che
easier the degradation.
The results o£ Grassie (20) and Hart (21), led to a
general agree.uen-'c -'cha-'c the higher -the molecular weigi:rt of
·the original pol:;lmer, the more dras-tic is tne drop in ·the
molecular weight o£ t.he residue. This fact was explained
by Madorsky (22) as sho~m in the follo"VTing mechanism.. De
gradation takes place by random scissions of chains. Be
cause of steric hindrance of the CH3 and COOCH3 groups on
alternate carbon atoms, tl1ese scissions cannot be accom
panied by a hydrogen transfer at the site of scission ..
Therefore, a scission results in the £ormation of t~1o free
radicals:
CH7. H CH3 H CH'2 H I v I 4 I I v I
--- c- c-c ------ c- c- c ~ I I I I I 1 C=O H C=O H C=O H I I : I OCH3 OCH3 .~ QCH3
• ~ YH3 ~ + c-c -c-----1 I I H C=O H
I OCH3
16
~i~hc :Eree radicals further dissocia-'ce to form monomers and
O@~ller free radicals:
H CH3 I H CH3 I I 1. I I ....-.-c-c --+-c-c· I I I I I H C=0 1 H C=O
1 I I OCH3
1 OCH3
H CH3 I I • ----l......... ---c-c I I H c=o
I OCH
3
~ YH3 + C=C
I I H C=O
I OCH3
, e·tc.
17
Grassie and Melville (20) also found that the activa
tion energy increases with extent of degradation of poly
(methyl methacrylate). They suggested that this might be
due to some process of strengthening of the bonds which
results in a greater activation energy. However, the in
crease in acti va·tion energy may be caused by the fact ·ti.1a:::
the weak links are eliminated in tJ.1e initial stage of de
gradationo Thus, the remaining bonds in the pol~ner are
the regular c-c bonds and are stronger than the wealc links 0
These mechanisms are not adequate to explain that the pro
ducts of degrada-tion generally con·tain monomers.
Straus and nadorsky (23), and Lehmann, Brauer, et al,
(24), analyzed the volatile products from the pyrolysis of
poly (methyl methacrylate) and sho\Ied that on degradation,
in the temperature range of about 150 to 500°C, poly -
(methyl methacrylate) yields almos·t 100 per cent monoraer.
ii.·t a higher temperature ( 525 °C), ·tile products, as analyze()
by gas chromatography, \-lere shown to be 96.2 per cent of
monomer, 3.6 per cent of gaseous products, and 0.2 per cent
of a residue.
Bywater and his associates (25, 26) investigated the
thermal degradation of poly (methyl me-thacrylate) in
18
diphenylether, o<-methylnaphthalene, and 1,2,4-tichloro
benzene solutions. The kinetics of depolymerization of
)01y (methyl methacrylate) was studied in the three sol
vents to assess the effect of solvent on the reaction.
The results show that the mechanism is the same in all sol
venas. The rate constant for chain initiation changes
little with solvent. The observed variations in rate are
primarily dependent on the magnitude of the chain transfer
constant which increases with the solvent series shown as
follows:
trichlorobenzene < diphenylether < o<-methylnaphthalene.
Grassie (27) was able to explain their-data asing the theory
that d.epolymerization at low temperature is initiated at
unsaturated end-groups produced with termination by dis
proportionation of macro-radicals.
Chen (28} studied the ther.mal degradation of poly
(methyl methacrylate) of different molecular weights in
toluene, ethyl acetate, and chloroform. Four poly (methyl
methacrylate) samples having molecular weights of
2,210,000, 7,3,000, '20,000, and 4,,000 respectively
19
were studied, each at two concentrations, 0.5 ; w/v and
1.0 ~ w/v. Using a constant temperature bath for heating,
he refluxed the polymer solutions for 10, 20, 30, and 45
hours at their normal boiling points, lll°C for toluene,
78°C for ethyl acetate and 64°C for chlorofor-m. The re
fluxing condenser was open to the atmosphere.
Molecular weight changes of the refluxed samples were
followed by viscosity measurements. ~s results showed
that the polymer having a molecular weight of 2,210,000
undergoes degradation in all solvents, with the loss of
solution viscosity increasing with increase in reflux
time. The most degradation occured in the chloroform and
toluene solutions, and the least in ethyl acetate. Thus,
degradation appeared to be more depend.ent on the nature of
the solvent than on the temperature.
For molecular weights of 7)3,000, 320,000, and 43,000
his results indicated that the viscosities of polymer
solutions increased with increase in reflux time up to
45 hours. He explained this last result as a case of re
verse polymerization. However, Chen's results showing an
increase in viscosity for low molecular weight samples
also could be explained by a loss of solvent during re
fluxing in his open system. This possibility could be
eliminated by using a closed system.
20
21
III. EXPERIMENTAL
A. Purpose of Investigation
The purpose of this study was to investigate the
thermal behavior of poly (methyl methacrylate) in solution
in a closed system at elevated temperatures as a function
of t~e, to gather basic information about the mechanism
of break down, and to find the molecular weight of polymer
after degradation assuming that the products of degrada
tion are essentially monomer units. The solvent chosen in
this work was 1,2-dichloroethane. Hereafter, poly (methyl
methacrylate) will be referred to as PMMA.
B. Plan of Investigation
When degraded ther.mally, the viscosities of polymer
solutions decrease with time where the extent of this de
crease is a function of temperature and type of solvent
used. The change in viscosities and molecular weight of
polymer as a function of reaction time were determined in
this investigation.
A cannon-Ubbelohde Dilution Viscometer, and a pycno
meter, as shown in Figure 2, were used for measuring the
rrf
(a)
• A B
c D
E
F
G
H
1
8 8
6 6
4 4
z l.
0 0
(b)
Figure 2 • (a) Cannon- Ubbelohde Viac:ometer
(b) Pycnometer
• See Appendix I
22
II
23
viscosities and densities of the solvent and the polymer
solutions at a constant temperature of 30°C. A glycerol
bath was set up for refluxing the polymer solution in
sealed Pyrex test tubes at elevated temperatures.
c. Methods of Procedure
1. Procedure for the use of the cannon-Ubbelohde
Dilution Viscometer is described in Appendix I.
2. Calibration of viscometer is described in
Appendix II and shown in Table I.
3. Density measurements by using pycnometer is
described in Appendix III and shown in Table II.
4. Viscosity, relative viscosity, intrinsic visco-
sity and molecular weight calculations.
Viscosities of solvent and solutions were obtained
as described in Appendix I. Relative viscosity is the
ratio of viscosity of solution and solvent:
= nsolution I nsolvent
Specific viscosity is defined as:
- - (nsolution - nsglventl nsolvent
(I·)
(J)
TABLE I
Viscometer CharacJceris·tics
Viscometer Viscome·ter Constan·ts A.Y.- B*
cannon-Ubbelohdc 0.00804 2 .. 30981
* A and B are defined by the equation as wri t·ten up in Appendix II.
24
25
TABLE II
Pycnometer Characteris·i:ics
Reading* Weight of Water Volume of 'tva ter
(gm) (ml)
5-2801 5-3029
5-3167
5-3194 5 .. 3424
13 .. 30 5-3624
* Readings re:Eer to calibration marks at 30°C for water., Density of wa·i:er at 30°C = 0.9957 gm/ml.
~ 01\
J.f Q) .fJ AS ~
'1-1 0
.fJ ~ Ol -rl Q)
~
5.40r------.------r------.------.-----~------~------
5-36
5-32
5.28
5.24~----~------~----~------L-----~------~----_J 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Pycnometer Reading
Figure 3. Relationship between pycnometer readings and weight of water at 30°C.
1\)
0\
then calculate Jche reduced viscosity from the following
equation:
= (4)
The intrinsic viscosity, (n), is independent of concen-
tration by virtue o£ extrapolaJcion_, c = 0, but is a func-
tion of solvent usede Intrinsic viscosity, (n), can be
obtained from "'che plot of nsp /c versus c, and extra-
polating to c = zero; ·the intercep-t is equal to (n).
Also, the correlation bet\veen in·trinsic viscosity a.nd
molecular weighJc of linear polymers is expressed in the
equation: (89,30)
(n) (5)
where K and a are constants deterrnined from a double
logari-thmic plot of intrinsic viscosi·ty and molecular
weight.. Both K and a are functions of the solven-t as
vvell as of the polymer type. K and a used in this
paper are shown in Table IIIe
The viscosity equation used in this paper is:
B t
(I)
28
Derivation of equation (6) is described in the appendix
section, Appendix IV.
5. Polymer samples - Two different samples of PMMA
having molecular weight of 2,050,000 and 43,000 were used
throughout this work. All samples were supplied by
Research Lab., Rohm & Haas co., in the for.m of powders.
The molecular weights were checked from dilute solution
viscosity data using ethylene dichloride and following
formula:
(n} =
The results are shown in Table III, and Figures 4 and 5,
pages 29, 31, and 33, respectively.
6. Solvent - Chemically pure reagent, ethylene di
chloride was used for preparation of polymer sample solu
tions. The physical properties of the solvent are given
in Table VI.
7. Polymer solution preparation and method of de-
gradation - Ten grams of polymer was dissolved in 1,000 cc
of solvent to make a 1.0 per cent w/v polymer solution.
Portions of this solution, approx~ately 30 cc each, were
29
TABLE III
Intrinsic Viscosi·::y-Ivlolecular Weight: Relationship
at 30 °C for PM.lflA Sarnples (Original)
Polyrner
PI1r-'1A 1
PHNA 2
Molecular Weight (Rohm & naas co.)
2_,050_,000
43_,000
(n)*
3.84
0.196
* calculated from equation:
(n)
4.20
(n) a = K H- in 1,2-dichloroethane where,
(n} -K -a -
X<1 -
intrinsic viscosity 5o3 x lo-5 0.77 raoJ_ecular weight.
** As reported in this. paper.
.J:-iol e cul ar Weight**
2,303,000
43,000
30
TABLE IV
Intrinsic Viscosi-ty of PNMA, Molecular Weight 2,303,000
Concentration
c
gm/100 m1
0.3484
0.3283
Oo2819
0.2292
0.1945
0.1929
0.1584
in 1,2-Dichloroethane at 30°C
Relative Viscosity
nR
3.1161
2-9539
2.6183
2.2345
2 .. 0274
2 .. 0075
1.8124
Specj_fic Viscosity
2.1161
1.9539
1.6183
1.2345
1.0274
1.0075
0.8124
Reduced Viscosi·ty
nso /c ""' 100 ml/gm
6o0738
5-9516
5-7413
5.3854
5.2823
5.2222
5.1287
Intrinsic viscosity • 4.20 100 ml/gm from Figure 4.
a ~ ...... E! 0 0 ...... ~
0
' g. s::
. 6.2
5.4
s.o
4.6
4.2
Intrinsic viscosity intercept) • 4.20
(from l.OO ml./gm
31
3.8--------~------~------~------~ 0 0.1 0.2
Concentration, c, gm/1.00 ml
Figure 4. Intrinsic viscosity of PMMA 1, Mol. Wt. = 2,303,000.
0.4
32
TABLE V
In-trinsic Viscosi i.:y of PWlA, Holecular \'leight 43,000
Concen tra·ti on
c
in 1.,2-Dich1oroethane at 30°C
Relative Viscosity
s::.:)ecific Viscosity
Reduced Vis cosi ·ty
nsp /c
gm/100 m1 100 rnl/ gm
0.8181 1.1624 0.1624 0 .. 1958
0.6533 1.1248 0.1248 0.1911
0.6221 1.1205 0 .. 1205 0 .. 1937
0.5047 1.0988 0.0988 0.1958
0.4978 1 .. 1017 0.1017 0 .. 2043
0.4124 1.0771 0 .. 0771 0.1869
Xntrinaic viscosity = 0.195 100 ~/gm from Figure 5.
0.30--------------~------~---------------
~ 0.20 ~ <o· . 00 0 -0 r-i a
0 0 r-i
.. ()
0.10 r . ......... Intrinsic viscosity (from intercept)
~ = 0.195 100 ml/gm s::
OoOO~------~------------~~------------~ 0 0.2 0.4 0.6 0.8 1.0
Concentration, c, gm/100 ml
Figure 5. Intrinsic viscosity of PMMA 2, Mol. Wt. = 43,000.
\)J \)J
TABLE VI
Physical Propert.ics of l_, 2-Dichloroethane at 30 °C
Boiling Point
Density
Viscosity
1 .. 2404 gm/ml
0. 7160 cen·tipoise
34
transferred to Pyrex teat tubes which were then sealed.
The tubes were placed in a constant temperature glycerol
bath kept at 50°C. After 4 1 12, 24, and 48 hours inter
vals samples were withdrawn from the bath, cooled to room
temperature, and then opened.
The density and the viscosity were then measured.
Viscosity and density measurements were made in a constant
temperature bath held at 30f0.2°C. The relative viscosity,
the intrinsic viscosity 1 and the molecular weight of each
sample were then calculated as described before.
Procedure NUmber 7 was repeated at a constant bath
temperature of g8.5°C.
IV. DATA AND RESULTS
Results are reported for the thermal degradation of
PMMA in 1,2-dichloroethane. All data were obtained as
9utlined in the experimental section, pages 21 to 35.
The results which are presented in both tabular and
graphical form, show the effects of initial molecular
weight, reaction time and temperature upon the thermal de
gradation of PMMA. The data and results are given sepa
rately for each temperature.
A. PMMA in 1,2-Dichloroethane at 50°C
The results for PMMA having initial molecular weight
of 2,303,000 are given in Tables VII, XV, and ~' pages
38, 53, and 55, respectively. Figures 6 and 13, pages 39
and 54, respectively, are.graphical representation of
these results. The results for PMMA having an initial
molecular weight of 43,000 are presented in Table VIII,
page 40, and in Figure 7, page 41.
:57
B. PHHA in 1, 2-Dic~rloroethane a·l: 98.5 °C
The resul·l:s for Pf"lMA having ini·tial molecular '\veiqht
of: 2,303,000 are given in Table IX and Figure 8, pages. 42
and 43, respectively; and, in Tables XI ·to XIV and
Figures 9 to 12, pages 45 to 52, respectively; and, in
Table XVI 1 page 55. The resul·ts for PI:~1A having an initial
molecular weight of 43,000 are presented in Table X,
page 44.
Sample :CJo.
1 1a 2 2a -;;:, -""
3a 4 4a 5 5a
'i'ABLE VI :t:
~i.1c:cual Dcsrada·tion o:C P!-'J.-:J\ l in
l, 2-D.icllloroe·thanc ut. 50 °C
(1 grrun Pol~ner in 100 m1 Solvent)
Re&CiiUon Ef£1ux Densj_·ty Time Time a·c 30°C
t ~ hrs sec nn/-rll ';;;J L l( --
0 840.0 l. 24J_ 0 840.3 1.241 4 829.0 1.240 4 833-7 1.240
12 816.0 1.240 12 816.0 1.240 24 807-3 1.240 24 807.8 1.240 48 777.6 1.240 48 776.1 1.240
38
Viscosit.y a·c 30 oc
·.n
centipoise
8.375 8.378 8.262 8.307 8.135 8.135 8.047 8.047 7-750 7-734
:59
J I
'
• u
0
I 0 It'\
.q -
co ~
..,. "' • .: "' ~ • 0
-~
k 0 roof
-6 ...t ry Q
l "' -~
roof
.: •
...t
~
..... .. I
1 -
..,. ! •
Oil ..
..., roof
0
I .: 0
• ...t
I ....
• •
+'
-\0
1
• .....
tJ k
...t i'
.....
" '0
r-f
"' <J
-• e • ~
4p •
\0
~
I I
I •
........ 0
k 0
0 0
0 0
::s •
• •
• •
~
0\
GO
t-
\0
In
...t
88lOdl~U80
"=>. <>' ..
~· u
40
TABLE VIII
Therr;lal Degradation o£ Pl·:ll·ll-1. 2 in
l, 2-Dichloroethane a-t 50 °C
( 1 gra1n Polyrner in 100 ral Sol vent)
Sample No.,. Reaction Efflux Density Viscosi-cy '.Ein1e 'l'in1e at 30°C at 7..0o,...
./ "' t ~ n
11rs sec gm/ml centipoise
1 0 89.5 1.240 0 .. 860 2 4 89.5 1.240 0.860 2a 4 89.5 1.240 0.860 3 12 89.0 1.240 0.855 3a 12 89.5 1.238 0.859 4 24 89.5 1.236 Oe858 4a 24 89.5 1.240 0.860
5 48 89.5 1.240 0 .. 860 5a 48 89.5 1.240 0.860
• • -g
10.0------~-----.-----,------.------.-----.----~
PMMA 1
~ 6.0 ..., I: • u ~
CJ 0
~ - Duplicate aaaple
~ 4.0 ..., ., I:
2.0
PMMA 2
8 16 24 '2 40 48
'l'ime, bra
Pigure 7. Ther.mal degradation of PMMA 1 and PMMA 2 in 1,2-dichloroethane at 50°C •
. . ····-···------- ·-··-··-·-·. ·····-·.- ··--·-···-·· ----------------
... ....
42
TABLE IX
Thermal Degradation of P11L,1A l in
1,2-Dichloroethane ai: 98.5°C
( l gram of PolyYaer in 100 ml Solven-t)
Sample No. Re&a.td.-on Efflux Density Viscosity Time Time aJc 30oC at 30°C
t ~ n
hrs sec ga/rnl centipoise
1 0 840.0 1.241 8.375 la 0 840 .. 3 1.241 8.378 2 4 818.3 1.240 8.153 2a 4 818.5 1.240 8.159 3a 12 783.6 1.240 7.808 4 24 720.0 1.238 7.164 4a 24 725 .. 0 1.240 7.225 5 48 565-3 1 2~9 5.626 -· ./
5a 48 566 .. 2 1.240 5 .. 635
Q) Ctl
.,-! 0 ~
.,.J .jJ d Q.) u
0\
u 0
~ .jJ RS
d
9-0r-----~-----T------.-----~-----T------~-----
fLo~ 6. - Duplicate sample
~
~ 7.0
6.0
0
s.o ~---:----:-:--~----L--..J__----'--_j 0 8 32 40 48 16 24
Time, hrs
Figure 8. Thermal degradation of PMMA 1 in 1,2-dichloroethane at 98.5°C. ~ \)J
44
TABLE
Therrnal Degradation of PH.l'iA 2 in
1,2-Dichloroetilane at 98.5°C
( 1 gram Polymer in 100 rnl Sol vent)
sample No., aeaeuon Efflux Density Viscosi·ty Time Time at 30°C a~c 30oC
t ~ n
l1rs sec gm/ml centipoise
1 0 89.5 1 .. 240 0.860 2 4 89.5 1 .. 238 0 .. 859 2a 4 89.5 1.240 0.860 3 12 90.1 1.240 0.866 3a 12 89 .. 5 1.240 0.860 4 24 89 .. 5 1.240 0 .. 860 4a 24 89 .. 5 1 .. 240 0.860 5 48 89.5 1.240 0.860 5a 48 89.5 1.240 0.860
45
TABLE XI
Intrinsic Viscosi·ty of P.t11-1A l After Degradation
Concentration Relative S:;_Jeci:Eic Reduced Viscosity Visoosj_ t.y Viscosi·ty
c nR nco nsp /c o_,_
gm/100 m1 100 m1/gm
0.3543 3 .. 1267 2.1267 6 .. 0024
0.2222 2.1680 1.1680 5-2567
0.1797 1.9183 0.9183 5.1114
0.1518 1 .. 7585 0.7585 4.9968
0.1247 1 .. 6080 0.6080 4.8759
Intrinsic viscosity = 4.2 100m1/gm from Figure 9.
7-0
6.0
0
Xntrinsic viscosity (from intercept)= 4.2 lOOml/gm
0.1 0.2 0.3
Concentration~ c~ gm/100 ml
0.4
Figure 9. Intrinsic viscosity of PMMA 1~ after degradation for 4 hours at 98.5°C, Mol. Wt. 2,303,000.
46
47
TABLE XII
Intrinsic Viscosity of Pl~IA l After Degradation
ConcenJcra·tion
c
grn/100 m1
0.3624
0.3351
0.2428
0.2240
0.1975
0 .. 1766
0 .. 1618
0.1295
for 12 Hours at 98.5•c
Re1a·tive Viscosi·ty
3.2163
3.0077
2.3299
2.2061
2.0313
1.9127
1.8208
1.6507
S?ecific Viscosi-ty
2.2163
2.0077
1 .. 3299
1.2061
1.0313
0 .. 9127
0 .. 8208
0.6507
Reduced ViscosiJcy
n 8 p /c
100 m1/gm
6 .. 1148
5 .. 9913
5 .. 4776
5 .. 3833
5 .. 2219
5.1690
5 .. 0734
5.0244
Intrinsic viscosity • 4.15 100 ml/gm from Figure 10.
48
7.0
6 - Dup1icate samp1e
6.0
~ ...... s 0
5.0 0 ...... ~
0
' 0. tQ
s:: Intrinsic viscosity (:from 4.0 intercept) - 4.15 l.OO ml./gm
0 0.1 0.2 0.4
Concentration, c, gm/100 m1
Figure 10. Intrinsic viscosity of PMMA 1, after degradation for 12 hours at 98.5°C, Mo1. Wt. = 2,267,000.
49
TABLE XIII
Intrinsic Viscosity of PMI1A l Af·ter Degradation
for 24 Hours at 98.5°C
Concentration Relative Specific Reduced Viscosity Viscosi-ty Viscosity
c nR nsp nsp /c
gm/100 ml 100 ml./gn
0.4447 3-7287 2.7287 6.1364 0.4073 3-3558 2-3558 5-7844 0.3215 2 .. 7037 1 .. 7037 5-2988 0.2848 2.5100 1.5100 5-3023 0.2695 2.3881 1.3881 5-1508 0.2214 2.1076 1.1076 5-0032 0.2018 1.9517 0.9517 4.7153 0.1839 1.8902 0.8902 4.0409 0.1410 1.6621 0.6621 4 .. 6960
Intrinsic viscosity • 3.68 100 ml./gm from Figure 11.
7-0r-----.------.------~----~------
6.- Duplicate sample
6.0
~ r-f a 0 ~ s.o
"' 0
' ~ s:: 4.0
L
Intrinsic viscosity (from intercept) = 3.68 100 ml/gm
o.s 3.0 ::--~-=---.1.---..1.--__j_--_j
0 0.2 0.4 0.3 0.1
concentration, c, gm/100 ml
Figure 11. Intrinsic viscosity of PMMA 1, after degradation for 24 hours at 98.5°C, Mol. wt. = 1,939,800. \Jl
0
51
TABLE XIV
Intrinsic Viscosity of Plv:II'-iA 1 After Degradation
for 48 Hours at 98.5°C
Concen·tration Relative Specific Reduced Viscosity Viscosity Viscosi-'cy
c nR nsp n 8 p/c
gm/100 m1 100 ml/gm
0.4560 3.2431 2.2431 4.9196 0.4453 3-1744 2 .. 1744 4.8830 0.3210 2.4326 1.4326 4.4629 0.3170 2.4037 1.4037 4.4279 0 .. 2541 2.0590 1.0590 4.1679 0.2483 2.0384 ]_.0384 4.1829 0.2108 1.8529 0.8529 4.0470 0.2020 1.8166 0.8166 4.0433 0.1552 1. 6036 0.6036 3.8897 0.1486 1.5711 0.5711 3.8442
J:ntrinsic viscosity • 3.31 100 m1/gm from Figure 12.
6.0 -------r------,r-----r------r---.--1
~ r-1 s.o a 0 0 r-1
.. ~
0. 4.0 ~Uj
6 - Duplicate sample
Intrinsic viscosity (from intercept) a 3-31 100 ml/gm
3.0~----~----~------~----~----~--~ 0 0.1 0.2 0.3 0.4 o.s
concentration, c, gm/100 ml
Figure 12. Intrinsic viscosity of PMMA 1 after degradation for 48 hours at 98.5°C, Mol. wt. = 1,690,400.
\J1 1\)
53
TABLE A.'V
Intrinsic Viscosi·ty of PMiwiA l Af·ter Degradation
ConcenJcration
c
gm/100 m1
0 .. 4053
0 .. 3138
0.2697
0 .. 2218
0.1990
0.1672
0 .. 1645
0 .. 1330
£or 48 Hours at 50°C
Relative Viscosity
3.4626
2.7832
2.4831
2.1806
2.0073
1.8222
1.8193
1.6436
Specific Viscosity
2.4626
1.7832
1.4831
1 .. 1806
1 .. 0073
0.8222
0.8193
0.6436
Reduced Viscosi·ty
n 5 P /c
100 m1/gm
6.0758
5.6828
5-4992
5 .. 3237
5.0629
4.916l
4.9814
4.8375
Intrinsic viscosity • 4.10 100 m1/gm from Figure 13.
7 oO ~--r-----,-----,-----r----
6.- Duplicate sample
6.0
~ r-1 a 0 0 s.o r-1
~
u
"' g. Intrinsic viscosity (from intercept) = 4.10 100 m1/gm s:: 4.0
3.0 0 0.1 0.2 0.3 0.4 0.5
Concentration, c, gm/100 ml
Figure 13. Intrinsic viscosity of PMMA 1 after degradation for 48 hours at 50°C, Mol. Wt. = 2,232,000.
\Jl ~
Temperature
oc
50.0
98o5
98-5
98o5
98-5
55
TABLE A.'VI
Nolecular Weight of PlvlHA 1 After
Thermal Degrada~ion
Heating Time
hrs
48
4
12
24
48
Molecular Weight
2,232,000
2,303,000
2,267,000
1_,939,800
1,690_,400
56
V. DISCUSSION OF RESULTS
The results of this investigation are discussed in
the same order as the data presented in the preceeding
section.
A. Thermal Degradation of PMMA, Molecular Weight 2,303,000
The effects of degradation of high molecular weight
PMMA on the viscosity of the polymer solutions in 1,2-di
chloroethane are shown in Figures 6 and 8, pages 39 and 43,
respectively. The viscosity of polymer solutions decreased
with increasing reaction time. When the reaction time was
kept constant, the viscosity of polymer solution decreased
with increasing temperature of reaction. Generally it can
be stated that the higher the molecular weight of a polymer
the higher the viscosity and the longer the chain length.
It has been postulated that the double bonds at the chain
ends, as a result of chain termination, are weak links (26,
27, '~). A possible mechanism is shown on page 57· It
has been generally accepted that the C=C bonds are more
subject to thermal and chemical attack than normal c-c
bonds. under certain conditions, where solvent radicals
may be present at elevated temperatures, they are probably
57
the only bonds which are attacked. In this case the exte~~
of clegracla tion o£ P.L•lMA with increasing reaction· tL.-~e c'~n be
explained by the following mechanism:
(a) The degradation at a given temperature stops at
some chain length, corresponding to a stage of degradation
where all links have been attacked. The viscosities of
polymer solutions will then approach a constant value. A
possible mechanism is:
H CH3 H CH3 H ·cHs
-c-c ---c-6 c=~ I I ........ I ~ I
H C = 0 tH\ C = 0 ?' C = 0 0CH3 "'"~,, OCHs / / OCHs
Long chain, weak links
r--/ H CH Ff yHs
---~-£ s-0-C==~=O 6cH3 OCHs
+ H CH., I l ._.
c=c I I
H c=O OCH~
y.i:l3
Y\. CH2 = C I C=O 0CH3
CHs CHs I
Monomers H CHs Ff -6-6--c=
I I H c=O
6 I C=O + -m CH2=y
C=O OCHs OCHs
I .
OCHs
Short1 stable chain ... \ .... . ..
58
The mechanism given on page 57, vnLile generally accepted,
is slightly misleading. A closer look at this mechanism
indicates that it is not the C=C bond tl~at is attacked
but rather the c-c bond alpha to the double bond which is
the weak link. Actually, C=C bonds are not \'leaker than
c-c bonds, they are more polarizable and therefore more
reactive. A more detailed version of the above mechanism
is shown belo\•1:
---/ ~
\'T-t, CH3 ,; -, titl:s._ ).. • -------- y ..._'f. - ... -·
H y=O H =
yH3 r y = 0
OCHs OCH3
! ------'-"-' c -==
!r
CH3 I c c===-o I OCHs
+ H CHs 9 ==-¢ H y=O
0CH3
(b) The degradation will proceed until almost all
polymer is converted to monomer. The viscosity of polymer
solution will decrease to the viscosity of methyl
59
methacrylate monomer.
If the above mechanisms are valid, the question arises
as to why the initial molecular weight of the polymer should
nave any influence on the degradation& ~~is study does not
give sufficient information to answer this question. How
ever, the low molecular weight PMMA does not behave in the
same mannero At this point it can be only postulated that
the high molecular weight PMMA degrades until a statistical
balance is obtained between the degraded polymer chain and
the newly generated monomer units, at which time it appears
reasonable to a.ssurne that a reverse polymerization mechanism
prevails. Such mechanism is discussed in the following
section.
B. Thermal Degra~ation of PMMA, t-iolecular Weight 43,000
It was found in the experiments with PMMA of molecular
weight of 43,000 that the viscosities of these solutions
remain fairly constant with increasing reacUon:: :~,..:;apto
48 hours, and temperatures upto 98.5°C in 1,2 dichloro
ethaneG This result can be explained as follows. The
chain-transfer mechanism is of the usual hydrogen-transfer
type (27). In the absence of transfer, and assuming
60
te~ination by disproportionation~ each molecule (radical)
must~ therefore~ be te~inated at one end by a catalyst
fragment.
~=free radical of catalyst
Initiation: CH3 H H CH3 I I I I •
R• + c - c ,... R-C -c I I I I
C=O H H C=O I J 0CH3 OCH3
Propagation: H CHs I I
I-I CH3 H CH3 H CHs I l.e R-C-C c= c __.R
1 h. ---f- c1 - c1
• y-T I I I I
H C=O I
OCHs
I I H C=O
I OCHs
H y=O H y=O OCH3 0CH3
'T\
Te~ination by disproportionation:
H yHs CHs H
+ .I I c-r· ,.., ,_,. ,.,_ ;ty ....... -.-:1-. I
rH' ~=0 / C=O H -<:.._ / I
/ OCH3 ......_ CHs ----- -! H CHs CHs ¥ I I + I
H-C <f .........
---- ---c=~ I
=0 y=O H
6cHs OCHs
61
In the above mechanism a free radical abstracts a
hydrogen atom from a carbon atom in the backbone of an
other chain which can become a polymer molecule with a
saturated end group as seen in the disproportionation re
action. For low molecular weight polymers, the polymer
chain is initiated at the end by either becoming activated
or by breaking off of a monomer unit. These monomers can
then add to a pol~uer radical or an activated monomer in
rapid succession, as in the propagation reaction during
polymerization. As a result the degradation process will
be a reverse polymerization for a low molecular weight&
This means the molecular weight of residue remains constant
upto some extent. It would be expected that if the reaO*ion
time and temperature were extended sufficiently that a de
crease in viscosity would occur and that the mechanism of
decomposition would be the same as that for the high
molecular weight polymer.
c. Molecular Weight of Polymer After Degradation
The molecular weight of the high molecular weight
samples after 48 hours decreased from 2,303,000 to
2,232,000 and 1,690,400 at 50°C and 98.5°C, respectivelyo
62
There has not been any change observed in the visco
sity of the low molecular weight solution for different
temperatures, and reaction times, which indicates that the
molecular weight of the low molecular weight polymer re
mains constant in the experimental range studied in this
thesis.
VI. LIMITATIONS AND RECOMMENDATIONS
1. The ther.mal degradation of poly (methyl
methacrylate) in solution in a closed system was studied
at 50°C and at 98.5°C. At a higher temperature, viz. 150°C,
the sealed samples always exploded. This may be due to the
high vapor pressure of 1,2-dichloroethane at that tempera
ture developed inside the sealed test tube. This may be
avoided by sealing the tube under vacuum. Thus, the pres
sure developed may not shatter the sealed test tubes.
Thermal degradation could then be studied at higher temper
atures.
2. It is suggested that the degraded polymer be frac
tionated and then analyzed for the products of degradation.
It would then be possible to obtain the rate data on the
different degradation processes.
3. The Cannon-Ubbelohde viscometer used for measuring
the viscosities was open to the atmosphere during testing.
There may be some error involved in the circulations due to
small amounts of solvent evaporation. Such an error can
possibly be eliminated by making the viscosity measurements
in a reversible viscometer.
64
VII. CONCLUSIONS
As a result of this study the following conclusions
were made:
1. The rate of thermal degradation of PMMA in solu
tion is a function of polymer molecular weights, tempera
ture, and reaction time •
. 2. PMMA having an average molecular weight of
2,303,000 degrades when its solutions in 1,2-dichloro
ethane are heated for same time at 50 or 98.5°C.
3. The role of the solvent on these degradation
processes may be that of a transfer agent.
1.
2.
3-
4.
5-
6.
7-
8.
g.
10.
11.
12.
65
VIII. BIBLIOGRAPHY
Staudinger, B., Brunner, M., Frey, K., Garbash, P., Singer, R., and Wherli, s., Ber., 62B, 241 (1929)., Ann., 468, 1 (1929): cf. Chern. Abstr. ~~ 2949 (1929).
Staudinger, H., and Steinhol~r, A., Ann., 5!I, 35 (1935): cf. Chem. Abstr. ~' 4336 (1935}.
Staudinger, H., Frey, K., Garbash, P., and Wherli, s., Ber., 62B, 2912 (1930); cf. Cham. Abstr. 24, 1564 (1930).
Schulz, G. v., and Busemann, E. z., Physik. Chem. 40, 524 (1948); (Reference No. 31, p. 181). --
Jellinek, H. B. G., and Spenaer, L. B., J. Polymer Sci. §., 573 ( 1952).
Jellinek, H. H. G., and b~:ner;,K. J., J. Polymer Sci. ll, 353 (1953).
Chen, s. w., J. Phys. & Colloid Chern • .5,2., 486 (1949).
cow1ey,~~P. R., and Melville, H. w., Proc. Royal Soc. (London} A210, 461 (1952).
Mesrobian, R. B., and Tobo1sky, A. v., J. Polymer Sci. a, 463 (1947).
Mesrobian, R. B., Metz, D., and Tobolsky, A. v., J. Am. Chem. Soc. ~ 785 (1945).
Montgomery, D. s., and Winkler, c. A., can. J. Research sg8, 407, 416, 429 (1950).
Thompson, J. o., J. Phys. & Colloid Chem. ~ 338 (1950).
caverhill, A. R., and Taylor, G. w., Polymer (London) ~ 19} (1965).
66
14. Bamford, c. H., Barb, w. G., Jenkins, A. D., and Onyon, P. F., .,Kinetics of Vinyl Polymerization by Radical Mechanisms", p. 239, Butterworths: London, (1958), (Reference No. 13, p. 195).
15. Morrison, J. A., Holmes, J. M., and Mcintosh, R., can. J. Research B24, 179 (1946): (Reference No. 31, p. 201).
16. Kuhn, w., Ber., ~~ 1503 (1930): (Refereace No. 22, p. 176).
17. Simha, R., J. Appl. Phys. ~, 569 (1941).
18. Blatz, P. J., and Tobolsky, A. v., J. Phys. Chem. ~ 77 (1945).
19.
20.
21.
22.
23.
24.
26.
Grassie, N., and Melville, H. w., Faraday Soc. Disc., g_, 377 ( 1947).
Grassie, N., and Melville, H. w., Proc. Royal Soc., Al99, 1 ( 1949).
Hart, v. E., J. Research Nat '1 Bur. Standards, .5.Q., 67 {1956).
lladorsky, s. L., .. Thermal Degradation of Organic Polymer", p. 179, John Wiley & Sons, Inc., New York (1964).
Straus, s., and Madorsky, s. L., J. Research Nat'l Bur. standards 66 A-B, 401 (1962).
Lehmann, F. A., and Brauer, G. M., Anal. Chem. 22, 673 (1961).
Grant, D. H., and Bywater, s., Trans. Faraday Soc. ~ 2105 (1963).
Bywater, s., and Black, P. E., Polymer Reprints, 2 372 (1964).
27.
28.
29.
JO.
31.
Grassie, N., "Chemistry of High Polymer Degradation Processes", p. }0, Interscience Pub., Inc., New York ( 1956).
Chen, Y. c., "Thermal Degradation of Poly (methyl methacrylate) in Solution in various Solvents", M. s. Thesis, University of Missouri at Rolla, (1965).
67
Billmeyer, F. w., "Textbook of Polymer Chemistry", p. 131, Interscience Pub., Inc., New York (1957}.
Tompa, H., "Polymer Solutions", p.273, Academic Press Inc., Butterworths Pub., London (1956).
Je.llinek, H. H. G., "Degradation of Vinyl Polymers", p. 29, Academic Press Inc., New York (1955).
68
IX. APPENDICES
Appendix I
Procedure for the Use of the cannon-Ubbelohde Dilu
tion Viscometer.
1. Clean the viscometer using suitable solvent
(such as acetone) and dry by passing clean, dry filtered
air through the instrument to remove the final traces of
solvento Periodically, traces of organic deposits should
be removed with a chromic acid-sulfuric acid cleaning
solutiono
2o If there is a possibility of lint, dust, or other
solid material in ~che liquid sample, filter the sample
through a sintered glass filter.
3. Place the sample in a constant temperature bath
at 30°C for 15 minutes. Charge a measured amount of sample
(about 10.0 ml) directly from the pipette through tube G
(Figure 2, page 22) in to the lower reservoir of the visco-
meter.
4. Place the viscometer into the holder and insert
it into the constant temperature water bath at 30°C• Verti
~ally align the viscometer in the bath.
69
5. Allow approximately 5 minutes for the sample to
reach the bath temperature.
6.. Place a finger over tube B and apply suction to
tube A until the liquid reaches the cen·ter of bulb c.. Re
move finger from tube B, and inunediately place it over tube
A until the sample drops from the lower end of the capillary
into bulb I. Then remove finger and measure the efflux
time.
7. To measure the efflux time, allow the liquid
sample to flow freely down past the e·tched mark D, measur
ing the time for the meniscus to pass from mark D to marJc
F, to the nearest 0.1 second (use stop watch}.
8. Without recharging the viscometer, make check
determination by repeating steps 6 and 7 until the efflux
time are nearly the same (approx. 0.1 second difference).
9. To calculate intrinsic viscosity of solution,
charge measured amount of solution (about 5 to 15 gram)
directly from the weighing buret through tube G into the
lower reservoir of ·the viscometer. Dilute samples by add
ing measured amount of solvent from the weighing buret.
Mix the original sample and the solvent by applying slight
pressure to tube B several times, and shaking the I.:.::.. s-::
70
viscometer.
10. Additional dilution may be made, if necessary,
by repeating steps 5 to 8.
71
Appendix II
Calibration of Viscometer.
For gravity type viscometers, the viscosity equation
is usually written as follows:
where,
_lL t
'V' = kinematic viscosity in stokes or centipoise
n - viscosity of solution in poises or centipoise
~ - density of solution in gm/ml
A - viscometer constant
t = efflux time in seconds,
(6)
B/t is called the l<.inetic energy correction. If the co-
efficient of tl1e kinetic energy correction is constant, it
may be said that B is constant.
The viscometer constant(the same at all temperatures)
A can be determined by using two or more standard oils
whose kinematic viscosities and densities at elevated
temperatures are known. The viscometer constant B can be
~imilarly determined. Pure water or pure solvent whose
viscosity and density are known can be used. Follow the r
72
procedure described in Appendix I observing the efflux
time, t. Substitute t into tl1e viscosity equation, equa
tion (·)~ to calculate the viscometer constants.
73
Appendix III
Density Measurements by Using Pycnometer.
Density of the solvent and the polymer solutions were
measured using a pycnometer as follows:
1. Clean the pycnometer using acetone, then dry by
passing dry ~iltered air or by using vacuum pumpe
2. Weigh the pycnometer to the nearest 0.0001 gram.
3. Charge the pycnometer with water (above 5 ml) by
applying pressure (using a rubber bulb). The water to be
used herein, is placed in a constant temperature bath at
30°C for 15 minutes.
4. Place the pycnometer into constant temperature
bath maintained at 30°C.
5. Allow approximately 5 minutes for the contents of
the pycnometer to come to bath tempe~ature.
6. Record the reading marks from the pycnometer.
7o Determine the total weight of water and pycno
meter to obtain the weight of water in the pycnometer.
8. charge the pycnometer with different volumes of
water (approxo 5 ml), repeat steps 3 to 7•
74
9. Plot the relationship between the reading marks
of pycnometer and weight of watero
lOo Charge the cleaned pycnometer with the samples
to be measured, and repeat steps 3 to 7.
llo The density of the sample under consideration,
at 30°C, is obtained from the weight of the sample (as
determined from the above-mentioned steps) divided by
the weight of wa-ter a-t the satae rcaaing.
75
Appendix IV
Derivation of Viscosity Equation used in this ~·'•·
The viscosity equation used in ·this paper '\vas derived
as follows:
If an energy and material balance is made about a
capillary viscome·ter, equation ( .. ""'~) is obtained:
(.8:')
where,
x1 - x2= vertical dis·tance bc·c\'lcen two menisci in viscometer
F = friction in capillary f
Fe= fricJcion due to strcar.1 contraction
F -e- fric-tion due to stream expansion.
F .c can be calcula·te<J by Poiseuilles law: I
where,
F f
L = capillary length
8LV_A ~ 9 1'( r4 ·t
u - average velocity of solu·tion in capillary
).{= absolute viscosity of solution
( ~,-.)
76
g - gravi ta·tional constant
~ - densi·ty o£ solution
D = capillary diameter
v - efflux volt-une
t = efflux time
and, r - capillary radius ..
Since both l<..,c and Fe have been correlated as a func>cion o£
kinetic energy, they can be added such that:
(m u2 I g) (18)
where m is the kinetic energy correction coefficient.
Equations ( ,.) and (10) can now be subs·tituted into equa-
tion ( 81) yielding equa·tion (11):
xl - =\{2 - 8LVA + m u2
.T( S g r4 t g (llia)
(nr~ tj 2
8LVA + m Xl - X2 =
n. ~ g r4 t g (11.)
Solve equation (11) for ..-L( /3 , kinematic viscosity, and
get equation (ll)s
.Ttg r4 t (xl - ~) 8 LV
m V (12) 8L.rct
77
Equa·tion (11-) is viscosity equation and is usually written
as follows:
n = At B
t (6)
X. ACKNOWLEDGEHENTS
The· author wishes to express his sincere appreciation
and gratitude to Dr. tvouter Bosch, Dean of Graduate School,
and Professor of Chemistry, for his guidance and advisory
during this research \vork.
Sincere thanks are extended to Drs. K. G. Nayhan,
J. L. Zakin, ana S. B. Hanna for thei~ ~1elpful adv:Lse ana
,.,,.lc':'c~~·;- · rl··10. .,,~-;ng J_-ll;S research WOr}C. t:)J,... :j .J - \--·- '--· .L ._. u \...L.- .1- '- .J..
Special thanks go to the Rohm and Haas Company,
Philadelphia, Pa., \'lho furnished the poly (methyl
methacrylate) fractions. used in this research work.
79
XI. VITA
The author, son of Pranjivandas and Sarojben Parikh,
was born a·t A11Iaedabad, India, on October 27, 1942.. He
a·t·tended Th.e Tutorial High School, A~u·:~edabad, IncJia, anCi
<;Jraduated in 1958. rn 1958, he joined Gujarat Univerisi~cy
and obtained his Bachelor's degree in Hathematics and
Physics in 1962.
He carne to ·t:1is country in Sep·tember 1962 and v1as
enrolled at the University of N.issouri at Rolla. He
received the degree of Bachelor of Science in Chemical
Engineering in June 1964.
Also, in January 1964, he was dually enrolled as a
graduate studen~c in the Department of Chemical Engineer
ing.