6 Ppd Enthalpy
-
Upload
thomasv501925 -
Category
Documents
-
view
27 -
download
4
Transcript of 6 Ppd Enthalpy
A study on the reaction between N-substitutedp-phenylenediamines and ozone: experimental results andtheoretical aspects in relation to their antiozonant activity
Franco Cataldo *
Soc. Lupi Chemical Research Institute, Via Casilina 1626/A, 00133 Rome, Italy
Received 8 June 2001; received in revised form 5 September 2001; accepted 6 September 2001
Abstract
The following p-phenylenediamines (PPD): N ,N ,N 0,N 0-tetramethyl-p-phenylenediamine (TMPPD), N ,N 0-dimethyl-
butyl-p-phenylenediamine (6PPD), N ,N 0-diaryl-p-phenylenediamine (DPPD), tris-(N -dimethylpentyl-p-phenylene-diamine)-N 0,N 0,N 0-1,3,5-triazine (6PPDTZ), have been oxidized under the action of O3 in diluted solutions. In all cases
the radical cation or semiquinone radical was the first derivative formed by monoelectronic oxidation of the substrate.
The radical cation has been studied by electronic spectroscopy and the electronic spectral changes of all mentioned PPD
has been followed as function of the ozonation time. The results have been discussed in the frame of the antiozonant
properties of these PPD which are used as antiozonant agents in diene rubber protection. It is shown that the an-
tiozonant activity of each PPD considered correlates with the free enthalpy of formation of the respective radical cation.
The lowest is the free energy of formation of a PPD radical cation and the highest is the antiozonant activity in a diene
rubber compound. � 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Ozone; p-Phenylenediamine (PPD); Radical cation; Semiquinone radical electronic spectroscopy; Antiozonant; Diene
rubber; Protection
1. Introduction
N ,N -substituted p-phenylenediamines (PPD) are the
most widely used antidegradant and antiozonants agents
for diene rubber [1,2]. Although other classes of anti-
ozonants are well known [2], and some of them find
some special application mainly in niche sectors, the
PPDs are by far the most effective and widely used
agents.
The general reaction mechanism of ozone with ali-
phatic and aromatic amines has already been proposed
and reviewed by Bailey [3] and by Rakovsky and Zaikov
[2]. In the present paper we would like to report our
experimental results obtained by electronic spectroscopy
concerning the ozonation of some commercially avail-
able PPD and of N ,N ,N 0,N 0-tetramethyl-p-phenylenedi-amine (TMPPD). The interpretation of the experimental
results has led us to clarify the early stage of reaction of
PPD with O3 which involve the formation of PPD rad-
ical cation followed by the formation of the quinone-
diimine (QDI) derivative.
Once clarified this mechanism, we show that by the-
oretical calculations it is possible to predict the reactivity
with O3 of any substituted PPD on the basis of the free
enthalpy of formation of the radical cation of each PPD
molecule.
2. Experimental
2.1. Materials and experimental procedure
In the present study, ozone has been generated elec-
trochemically [4], as in all our previous studies [5–10]
European Polymer Journal 38 (2002) 885–893
www.elsevier.com/locate/europolj
* Tel.: +39-06-205-5084; fax: +39-06-205-0800.
E-mail address: [email protected] (F. Cataldo).
0014-3057/02/$ - see front matter � 2002 Elsevier Science Ltd. All rights reserved.
PII: S0014-3057 (01 )00248-8
and the PPD used were commercial grades N ,N 0-di-
methylbutyl-p-phenylenediamine (6PPD), N ,N 0-diaryl-
p-phenylenediamine (DPPD), tris-(N-dimethylpentyl-
p-phenylenediamine)-N 0,N 0,N 0-1,3,5-triazine (6PPDTZ).
The latter PPD is a relatively new and non-staining anti-
ozonant commercialized under the trade name of Du-
razone � by Uniroyal Chemicals. Only TMPPD
di-hydrochloride has been purchased from Aldrich.
The ozonation reactions were conducted in analytical
grade CHCl3 from Fluka or in distilled water solution
by bubbling the ozonized oxygen into the PPD solu-
tions. The average ozone content by weight over oxygen
was about 10% and was determined iodometrically [4].
Ozone was produced at a rate of 3:43� 10�7 mol/min in
all cases. The solution volume used in each ozonation
study was 25 or 50 ml as specified case by case in the
text. After opportune intervals of ozonation times the
electronic spectra have been recorded on a Shimadzu
UV160A spectrophotometer.
2.2. Theoretical calculations
The theoretical calculations concerning the free
enthalpy of formation of the molecules considered in
this work have been conducted by using AM1 method.
Also the free enthalpy of formation of the radical cation
of each molecule has been calculated with the same
method, by extracting one electron from one nitrogen
atom.
3. Results and discussion
In our previous works [7,8] which we have reviewed
recently [11,12], we have shown that long unsubstituted
and substituted polyene chains generate radical cations
as one of the first elementary reaction act with ozone.
We have proposed a new electrophilic mechanism ofScheme 1.
Fig. 1. Electronic spectra of TMPPD. (A) Pure TMPPD–2HCl
1:77� 10�4 M in H2O. (B) Same as in A after 5 s (� � �) and after
300 s (––) ozonation. (C) TMPPD–2HCl 5:65� 10�4 M in H2O
from bottom to top respectively after 25, 65 and 120 s ozona-
tion. (D) TMPPD 4:22� 10�5 M in CHCl3: the curve with the
peak at 264 nm is the original solution. The solid line with
peaks at 565 and 614 nm is after 120 s ozonation and the dotted
line is the spectrum after the discolouration from blue to pink.
On top of these two curves the other more intense curves were
recorded after 240 s ozonation (––) and after colour fading to
pink (� � �).
886 F. Cataldo / European Polymer Journal 38 (2002) 885–893
conjugated addition across conjugated double bonds
when ozone or other electrophiles [13,14] cause the
addition reaction. Moreover, we have shown that it is
possible to generate C60 fullerene radical cations in su-
peracid solutions [15].
In the case of PPD, the formation of a radical cation
as the first elementary reaction step is a very well known
experimental fact when the oxidizing agent is bromine in
minute amounts [16]. In fact a stable radical cation,
known as Wurster’s complex or salt is formed [16]. Of
course many other different oxidizing agents have been
tested and the reaction has been found [17,18] to be
second order overall, but first order with respect to the
PPD and the oxidant. The values of the second order
rate constants for the formation and the decay of the
PPD radical cation were found to be in line with the
oxidation potentials of the oxidant [17,18]. We have
shown in a previous paper [9] that chlorine (E0 ¼ 1:36 V)and ozone which are stronger oxidizing agents than
bromine (in fact E0 O3=O2 ¼ 2:07 V while for E0 for
Br2=Br� ¼ 1:065 V) are able to form the radical cation
of PPD, provided that they are used in small amounts
over the organic substrates.
As shown in Scheme 1, the formation of a radical
cation from a PPD derives from the one-electron oxi-
dation of PPD. Once formed the radical cation is rela-
tively stable but could be further oxidized to a QDI
derivative by loosing another electron. It is interesting to
note that the reaction between QDI and unreacted PPD
leads to the formation of two radical cation molecules.
This means that until in the reaction system remain a
certain amount of unreacted PPD molecules, we will
have a buffering effect which hinder the oxidation of the
radical cation to the QDI. Infact each QDI formed is
reduced back to the radical cation by the oxidation to a
radical cation state of another PPD molecule.
3.1. About the ozonation of TMPPD
In Fig. 1A is reported the spectrum of TMPPD–
2HCl (about 1:77� 10�4 M) in water. It is characterized
by three maxima respectively at about 200 (e ¼ 13; 180),254 (e ¼ 13; 720) and 319 nm (e ¼ 2250). These three
bands correspond to the three bands of unsubstituted
PPD ([19], spectrum D9/99) respectively at 197 (e ¼33; 500), 241 (e ¼ 9300) and 305 nm (e ¼ 1900). These
bands are generated from p ! p� transitions.
According to Baude notation [20] the band at shorter
wavelength is called E1, followed by E2 and by the B
(benzenoid)-band at longer wavelength. The intense E1-
band at shorter wavelength derives from an allowed
transition whereas the other two bands result from
forbidden transitions in the highly symmetrical benzene
molecule. In the B-band there is a contribution derived
from the n–p interaction of the nitrogen atoms of the
PPD with the p electrons of the benzene ring. When O3
is passed in the solution of TMPPD–2HCl in water, a
new band is observed (Fig. 1B and C). This new band
shows a double peak at 562 and 610 nm and is due to the
radical cation of the TMPPD [16,21] and is generated
since the early reaction stages of O3 with the amine [21].
The formation of the TMPPD radical cation is accom-
panied also by the parallel growth of the TMPPD B-
band at 320 nm (see Figs. 1B, C and 2). In fact, the
320 nm band under the action of O3 undergoes an
hypschromic shift to 300 nm and increases its inten-
sity, reaching a maximum and decreasing (see Fig. 2),
following the same trend of the other bands assigned to
Fig. 2. Ozonation of TMPPD-2HCl 1:77� 10�4 M in H2O: evolution of the optical density of the bands associated to TMPPD (200
and 254 nm) and to its radical cation (319, 561 and 609 nm).
F. Cataldo / European Polymer Journal 38 (2002) 885–893 887
the radical cation in Fig. 2. This behaviour clearly sug-
gest that also this band is related to the formation of the
radical cation and the electronic structure of the radical
cation has an hyperchromic effect on the B-band of
TMPPD and the PPD in general.
From the literature [16] it is known that e560 ¼ 11,500
while e610 ¼ 11,000. By using these data and the changes
in concentration of PPD as function of ozonation time,
and knowing the approximate ozone amount bubbled
into the reaction mixture it is possible to estimate the
molar ratio between the most interesting chemical spe-
cies involved. In Table 1 we have summarized our results
which show that the highest molar ratio of radical cation
formation over the ozone supplied occurs in the early
seconds of ozonation due to the monoelectronic oxida-
tion act which leads to the radical cation. For instance
the maximum molar ratio between the concentration of
the radical cation and ozone is reached after 5 s of re-
action (see Table 1) and it appears that there are more
than four radical cation molecules for each O3 molecules
(under the assumption that all O3 bubbled into the so-
lution has reacted). This fact gives an idea of the excel-
lent scavenging effect of PPD towards O3. After 5 s of
reaction, 1/24 of all TMPPD molecules has already been
oxidized and transformed into the radical cation (Table
1). Of course the radical cation is just an intermediate
which in the case of TMPPD is relatively stable and its
further oxidation is for a certain period hindered by the
reducing effect of the unreacted TMPPD as discussed in
Section 1 (see Scheme 1).
However, as stated by Bailey [3], other competitive
reactions occur in substituted tertiary PPD such as the
alkyl side chain oxidation, which involves the proton
abstraction mechanism. This reaction is reported to be
slow and to lead, in the case of TMPPD, to N ,N 0-di-
methyl-p-quinonediimine and other products, as can be
deduced from the ozonation of N ,N 0-dimethylaniline [3].
It is also interesting to note that when the band at
about 300 nm reaches its maximum concentration, the
Table 1
Concentration molar ratio of the species involved in TMPPD
ozonation
Time (s) Radical ca-
tion/ozone
(molar
ratio)
TMPPD/
Ozone
(molar
ratio)
TMPPD/Radical
cation (molar
ratio)
0 0 0.0
5 4.4 104 23.8
15 2.5 35 13.7
60 1.4 7 5.1
120 1.1 3 2.9
180 0.8 1.68 2.0
300 0.6 0.69 1.2
480 0.3 0.25 0.9
720 0.05 0.15 0.5
1200 0 0.07 0.0
Fig. 3. Electronic spectra of 6PPD. (A) Pure 6PPD 7:5� 10�5
M in CHCl3. (B) Same as in A after 15 s ozonation. (C) Same as
in A after 30 s ozonation. (D) Same as in A after 60 s ozonation.
(E) Same as in A after 90, 120, 180, 240, 360 s ozonation (re-
spectively from top to bottom) in CHCl3.
888 F. Cataldo / European Polymer Journal 38 (2002) 885–893
molar ratio between the still unreacted TMPPD and its
radical cation approximates to the unity (see Table 1 and
compare with Fig. 2), the TMPPD/O3 molar ratio is 0.7
and also the other radical cation bands at longer
wavelength reach their maximum. From Fig. 2 it is clear
that all TMPPD has been quite completely consumed
after 400 s of ozonation so that the ozone attack is now
directed to the oxidation of the radical cation whose
concentration in fact starts to decline. As shown in
Scheme 1 one of the reaction products derived from
further monoelectronic oxidation of the radical cation is
the QDI derivative.
The ozonation of a QDI structure involves both the
O3 attack to C@N double bonds as well as to C@C
bonds of a quinoid structure. The general guidelines of
these further degradation reactions have been discussed
by Bailey [3].
When the free base TMPPD is dissolved in CHCl3and ozonated, the blue colouration of the Wurster com-
plex can be observed demonstrating that also in non-
polar solvents the radical cation is formed under the
action of O3. In diluted CHCl3 solution the radical ca-
tion band appears as a doublet at 565 and 614 nm, as in
the case of water solution. In more concentrated CHCl3solutions (for instance at 4:22� 10�5 M of Fig. 1D) the
radical cation band of TMPPD appear more complex
with two additional features at 481 and 519 nm in ad-
dition to the other normal bands at 565 and 614 nm. In
these conditions, immediately after ozonation (120 s at
the usual O3 feeding rate) the solution appears blue but
after the interruption of the passage of O3, after 1 min,
the solution becomes pink and the two radical cation
peaks at 565 and 614 nm vanish in a band tail while the
other two bands at 481 and 519 nm remain almost un-
changed (see Fig. 1D). Further ozonation restores for a
short time the blue colour which turns back pink (Fig.
1D). These experimental facts suggest that in CHCl3 the
TMPPD radical cation is not stable free but it forms a
dimeric complex [22].
In 10% HCl solution TMPPD shows a unique maxi-
mum at 232 nm and a shoulder at 260 nm. When O3 is
bubbled into the solution for 30–60 s, the peak shifts to
246 nm and two new bands appear at 312 and 432 nm
(broad). By further ozonation the band at 246 nm shifts
back to 232 nm, hence this phenomenon indicate that in
the early ozonation stages there is the formation of a
charge-transfer complex between TMPPD and O3. The
band at 434 nm is due to the diprotonated radical ca-
tion. Protonation of amines typically causes the hypso-
chromic shift of their B-bands [20]. Thus, it is obvious to
expect the radical cation band of diprotonated TMPPD
lying at 434 nm instead of at 560 and 610 nm as it
happens in non-acidic media. After 60 s ozonation this
band is no more observable. Instead, what it has been
observed is the steady growth of the band at 312 nm as
function of the ozonation time and its slow shift to
306 nm. The position of this band is almost the same as
observed in non-acidic water solution as described pre-
viously and it is due to the radical cation.
3.2. About the ozonation of 6PPD
Contrary to the tertiary amine TMPPD, 6PPD is an
N-alkyl–N 0-aryl disubstituted secondary amine. It is the
most widely used antiozonant for tyre application to
protect the diene rubber [1]. In CHCl3 6PPD shows a
maximum at 290 nm (Fig. 3A). By using 25 ml of a
6PPD solution of 7:5� 10�5 M, after 15 s ozonation we
observe the growth of a new band at 388 nm with two
Fig. 4. Ozonation of 6PPD 7:5� 10�5 M in CHCl3: evolution of the optical density of the band associated to 6PPD (290 nm) and to its
radical cation (410 nm).
F. Cataldo / European Polymer Journal 38 (2002) 885–893 889
shoulders at 410 and 480 nm (Fig. 3B). On further ozo-
nation the shoulder at 410 nm becomes a peak and in-
cluded the band at 388 nm while the shoulder at 477 nm
undergoes a gradual batochromic shift to 483 nm (after
30 s, Fig. 3C) and to 500 nm (after 60 s, Fig. 3D). Ad-
ditional ozonation causes a broadening of the band at
410 nm which buries the shoulder at 500 nm (Fig. 3E).
The radical cation of pure unsubstituted PPD ap-
pears at 462–479 nm [16] and is accompanied by a
pronounced peak at 380 nm, as we have verified by
ozonating pure PPD in CHCl3. Thus it is obvious to
assign the band at 388 nm with the shoulder at about
480 nm to the 6PPD radical cation. In the early stages,
the ozonation proceeds with the accumulation of the
6PPDþ in the solution, thanks to the mechanism of
Scheme 1 which hinders the formation of the QDI de-
rivative. This is clearly illustrated in Fig. 4 where we can
observe that the rapid drop in the concentration of the
6PPD is compensated by the accumulation of the radical
cation. After 60 s the radical cation starts to be degraded
by O3. Among the products there is certainly the QDI
derivative which still absorb at 400 nm or at longer
wavelengths, but there are also several other derivatives
some of them have been identified with chromatographic
techniques [23].
3.3. About the ozonation of DPPD
DPPD is another well known antiozonant. It is a
diaryl-substituted PPD and it is a commercial mixture
of N ,N 0-phenyl–tolyl, N ,N 0-tolyl–tolyl and N ,N 0-diphe-
nyl-PPD. By itself, it is not a particularly effective an-
tiozonant in rubber compounds when used alone [1].
However, in combination with 6PPD it has sinergistic
effects and ensures long protection to the rubber good
[1].
In CHCl3, DPPD shows a shoulder at 246 nm and a
peak at about 300 nm (Fig. 5A). The ozonation of 25 ml
of a 7:2� 10�5 mol/l solution causes the rapid growth of
the radical cation band at 411 nm (Fig. 5B, C). This
band shifts slowly to 415 nm and simultaneously we
observe a reduction of the band at 300 nm. By plotting
the absorbance of these two bands as function of the
ozonation time (Fig. 6), we get a graph which is very
close to that obtained by ozonating 6PPD (compare
with Fig. 4). Thus the band assignment and interpreta-
tion is analogous. The ozonation of the DPPD can be
followed by the drop in optical density of the band at
300 nm. The band at 246 nm which is due to the aryl
rings of the N ,N 0-substitution survives to the ozonation
and in fact the optical density of this band remains
unchanged even after prolonged ozonation (see Fig.
5D).
By comparing the Figs. 4 and 6 which refer respec-
tively to 6PPD and DPPD solution of approximately
equal concentration it appears evident that the maxi-
mum concentration of the radical cation occurs in both
cases after about 60 s of ozonation. This is in line with
literature data which show that in CCl4 the ozonation
rate is equal for both PPDs [2]. However, the con-
sumption rate of the 6PPDþ appears faster than that of
DPPDþ.
3.4. About the ozonation of 6PPDTZ
The antiozonant 6PPDTZ is rather new and it is non-
staining [1]. The ozonation of a CHCl3 solution 5:45�10�5 mol/l causes a steady reduction of the band origi-
nally lying at 297 nm. This band shifts to 275 nm after
30 s ozonation. By following this band it is possible to
Fig. 5. Electronic spectra of DPPD. (A) Pure DPPD 7:2� 10�5
M in CHCl3. (B) Same as in A after 20 s ozonation. (C) Same as
in A after 35 s (––) and 50 s (� � �) ozonation. (D) Same as in A
after 80, 120, 150, 210 and 300 s ozonation (respectively from
top to bottom) in CHCl3.
890 F. Cataldo / European Polymer Journal 38 (2002) 885–893
follow the consumption of the 6PPDTZ (see Fig. 7). A
more concentrated solution of 6PPDTZ (1:19� 10�4
mol/l) shows also a B-band at 487 nm. Ozonation causes
the development of a series of bands in the same spectral
region having a features which recall that of ozonated
TMPPD in CHCl3. Four different bands appear re-
spectively at 466, 483, 503 and 525 nm with the latter
being the most intense (see Fig. 8). The position of this
band is compatible with the assignment to the radical
cation. The optical density of the 525 nm band is re-
ported as function of the ozonation time in Fig. 8 for the
1:19� 10�4 M solution. In the case of this molecule the
prolonged ozonation causes the solution to become
dark. It appears that ozone causes the formation of
polycondensation products. The ozone attack can be
directed not only to PPD groups but also to the triazine
Fig. 6. Ozonation of DPPD 7:2� 10�5 M in CHCl3: evolution of the optical density of the band associated to DPPD (300 nm) and to
its radical cation (414 nm).
Fig. 8. Electronic spectrum of 6PPDTZ 1:19� 10�4 M in
CHCl3. Detail of the radical cation band after 200 s ozonation.
Fig. 7. Ozonation of 6PPDTZ 5:45� 10�5 M in CHCl3: evolution of the optical density of the band associated to 6PPDTZ (297 nm)
and to its radical cation (525 nm), measured in the 1:19� 10�4 M in CHCl3 solution.
F. Cataldo / European Polymer Journal 38 (2002) 885–893 891
ring although in this case the reaction speed should be
slower than that with the PPD.
3.5. Discussion of the theoretical calculations and con-
cluding remarks
Although the ozonation of secondary amines leads to
the formation of nitroxide radicals as the main products
as shown by Razumovskii and Batashova (as cited in
Ref. [3]) the general interpretation of the ozonation of
the secondary aromatic PPD involve the formation of
the corresponding radical cations as the first reaction
derivative [3]. Our study has confirmed the correctness
of this interpretation.
The experimental results reported in the previous
sections have confirmed once again that all PPDs gen-
erate the respective radical cation as the first elementary
intermediate when oxidized with O3. It has also been
reported [2] that the most powerful antiozonant PPDs
lead to the formation of stable radical cation interme-
diates while the less effective generate unstable radical
cation intermediates.
This led us to run some calculations according to
AM1 as stated in the Experimental section. We have
calculated the free enthalpy of formation of several well
known PPDs reported in Table 2, the free enthalpy of
formation of the radical cation and the corresponding
free energy of reaction which led to the radical cation.
The most surprising thing we are showing in Table 2 is
that the free energy of formation of the radical cation of
each PPD considered correlates with the antiozonant
activity as experimentally observed in the rubber vul-
canizates [24] without making any consideration on the
molecular weight and diffusion rate constants. More in
detail, the lowest is the free energy of formation of a
radical cation, and the highest is its antiozonant activity.
As well known [1] N ,N 0-dialkyl-substituted PPD are
better antiozonants than N ,N 0-aryl–alkyl-PPD which in
their turn are better than N ,N 0-diaryl-PPD.
Thus, in principle, to design new antiozonants or to
predict their antiozonant activity it could be possible for
the future to apply the proposed approach which in-
volves the calculation of the free energy of formation of
the corresponding PPD.
Acknowledgements
My warm thanks to Mr. Paolo Mondini for the com-
putational calculations according to the AM1 method.
References
[1] Cataldo F. Polym Degrad Stab 2001;72:287.
[2] Rakovsky S, Zaikov G. Kinetics and mechanism of ozone
reactions with organic and polymeric compounds in liquid
phase. New York: Nova Science; 1998.
[3] Bailey PS. Ozonation in organic chemistry. vol. 2. Non-
olefinic compounds. New York: Academic Press; 1978.
[4] Cataldo F. Recent Res Devel Electrochem 2000;3:61, 79.
[5] Cataldo F, Heymann D. Polym Degrad Stab 2000;70:237.
[6] Cataldo F, Ricci G, Crescenzi V. Polym Degrad Stab
2000;67:421.
[7] Cataldo F. Polym Degrad Stab 1998;60, 223, 233.
[8] Cataldo F. Polym Degrad Stab 1996;53:51.
[9] Cataldo F. Eur Polym J 1996;32:43.
[10] Cataldo F, Ori O. Polym Degrad Stab 1995;48:291.
[11] Cataldo F. Polym Degrad Stab 2001;73:511.
[12] Cataldo F. Proceedings of RubberChem ’01, 3rd–4th April
2001, Brussels, Belgium, Paper 2. Shawbury: Rapra Tech-
nology.
[13] Cataldo F. Eur Polym J 1992;28:1493.
[14] Cataldo F. Eur Polym J 1993;29:1635.
[15] Cataldo F. Spectrochim Acta 1995;51A:405.
[16] Jaff�ee HH, Orchin M. In: Theory and applications of
ultraviolet spectroscopy. New York: Wiley; 1962. p. 464.
[17] Maruthamuthu P, Venkatasubramanian L, Dharmalingam
P. J Chem Soc Faraday Trans I 1986;82:359.
[18] Aravinan P, Maruthamuthu P, Dharmalingam P. Int J
Chem Kinet 1995;27:109.
Table 2
Antiozonant activity: correlations between calculations and experimental facts
Molecule Enthalpy of formation of
the PPD (kJ/mol)
Enthalpy of formation of the
radical cation (kJ/mol)
Antiozonant
activity (rating)
Fatigue crack
formation (rating)
Antioxidant
activity
(rating)
77PD �176 571 100 70 42
IPPD 126 774 95 100 70
6PPD 143 793 70 92 70
(6PPD)3-
triazine
196 963 60 75 60
DTPD 356 1025 50 65 70
DPPD 420 1094 35 50 70
DNPD 581 1254 0 0 100
892 F. Cataldo / European Polymer Journal 38 (2002) 885–893
[19] Perkampus HE. UV–VIS atlas of organic compounds.
Weinheim: Wiley-VCH; 1992.
[20] Silverstein RM, Bassler GC, Morrill TC. Spectrometric
identification of organic compound. 4th ed. New York:
Wiley; 1981 [Chapter 6].
[21] Layer RW. Rubber Chem Technol 1966;39:1584.
[22] Kamisuki T, Hirose C. Spectrochim Acta A 2000;56:
2141.
[23] Layer RW, Lattimer RP. Rubber Chem Technol 1990;
63:426.
[24] Hofmann W. Rubber technology handbook. Cincinnati:
Hanser/Gardner; 1994.
F. Cataldo / European Polymer Journal 38 (2002) 885–893 893