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Organotin compounds as stabilizers of thermal degradation of fluorine-containing polymers
Thermal degradation of fluorine-contalning polymers
1667
REFERENCES
1. J. MORRISON, W. CAMPBELL and O. MAASS, Canad. J. Res. 18B: 168, 1940; OKAMURA Naturwissenschaften 21: 328, 1933 2. N. V. MIKHAILOV and E. Z. FAINBERG, Koll. Zh. 18: 315, 1956 3. W. REESS, J. Text. Inst. 39: T351, 1948 4. J. GUTHRIE, J. Text. Inst. 40: T489, 1949 5. H. MARK, Quot. from Bil'meier, Introduction to Polymer Chemistry and Technology, 27, 1961 6. W. MORTON and J. HEARLE, Physical Properties of Textile Fibres (monograph), Manchester, Butterworths Textile Institute, 179, 1962 7. J. J. MANN and H. J. MARINANN, Trans. Faraday Soc. 52: 481, 1956
ORGANOTIN COMPOUNDS AS STABILIZERS OF THERMAL DEGRADATION OF FLUORINE-CONTAINING POLYMERS N. S. GASHTOL'D, A. F. DOKIrKINA, K. A. KOCHESKKOV and T. V. TAY~AT,AYEVA M. I. KaUnin Polytechnical Institute, Leningrad (/~eceived 17 June 1966) S~VV.RAL reports have appeared in the literature [1] regarding the stabilizing effect of organotin compounds which improve the heat resistance, thermal stability and fastness to light of polymeric materials based on polyvinylchioride. The present report is based on stabilizers of this t y p e and the thermal degradation of fluorine-containing copolymers of a,fl,fl-trifluorostyrene (and its p-methyl- and m-methylsubstituted isomers) with styrene and 2,5-dimethylstyrene. The substances investigated were five copolymers differing as to their fluorine content (18 to 2 5 ~ ) and as to the number of methyl groups in the benzene rings (Table 1, [2]). The stabilizers were: di-n-butyltin maleate, di-n-butyltin dicaprylate and di-n-butyltin dilaurate. Samples of the copolymers containing no stabilizer were investigated, as well as mechanical mixtures of the polymers and organotin compounds listed above. The stabilizer content of the copolymers varied from 3 to 50/o. The degradation of two types of sample was investigated: powders and press-moulded discs 2-4 m m thick and 8-10 mm in diameter. The estimated amount of thermal degradation was based on: the weight loss, measurement of the exterior of the sample, the fluorine content [3], solubility, and changes in the maximum viscosity number (MV~). Nuclear magnetic resonance and electron paramagnetic resonance spectra were recorded for several of the thermally treated samples, and interpreted. * Vysokomol. soyed. Ag: No. 7, 1489-1493, 1967.
1668
N . S. GASHTOL'D e$ a/.
The samples were heated in air in a flask (the control samples were vacuumheated) fitted with an electric heater: measurement and control of the temperature was eifected b y means of an automatic electronic self-recording d.c. bridge (type E1VII)-ll2) using a platinum resistance thermometer situated inside the heater. The temperature control was accurate to ~:0.5 °. The temperature of the sample was determined with an iV[S-I-01 device the resistance thermometer of which was in the flask below a support with the sample. The MVN values were found b y viscometry at 20.0-4-0.1 °. using an Ubbelohde viscometer and solutions of the polymers in benzene. The degradation temperatures were selected as follows: the lower limit was 40 to 50 ° higher t h a n the heat resistance of the copolymer (found b y I R pyrolysis) and the upper limit was determined from the abrupt change in the weight of the samples. DISCUSSION OF RESULTS
Two series of tests were carried out during investigation of the thermal degradation of fluorine-containing copolymers: with and without stabilizers. In the first series of tests samples of copolymers I I - Y (Table 1) were kept for different times (from 0.5 to 22 hr; for sample I I I up to 200 hr) at temperatures of 180-230 °. TABLE 1. COMPOSITIO~ AND PROPERTIES OF COPOLYMERS UI~DER REVIEW [2]
Copolymers
I II III
IV V
~.,fl,fl-Trifluorostyrene + styrene a,fl,fl-Trifluor-]- 2,5-diinethylstyrene 3-Methyl-~,fl,fl-trifluorostyrene ~-styrene 4-Methyl-~,fl,fl-trifluorostyrene ~styrene 4 -Methyl-a,fl,]Ltrifluorostyrene -~ 2,5-dimethylstyrene
Composition of Heat recopolymer, sistance MVN mole % by IR fluorine pyro-I 20° corn- styrene lysis,°C ~ ponent
Fluorine content of eopolymer, ~/o
39"8 63.6
60.2 36.4
148 164
2"9 0-5
18.1 23.6
74.2
25-8
139
0-2
27.4
54.3
45.7
148
0.5
22-0
69.4
30.6
171
0.6
24.7
The change in weight in relation to heating time was approximately the same for all the copolymers and was unaffected b y the form of the sample under investigation (powder or disc), A t temperatures 40 ° higher than their heat resistance limit the copolymers either suffered a weight loss of 0.5 to 2% during the initial period, after which their weight remained constant, or else there was a gradual b u t very slow change in their weight, the total change in 12-20 h r being 3 to 4%. I f the temperature is raised b y a further 20-50 ° rapid degradation of
Thermal degradation of fluorine-containing polymers
1669
the sample is observed, with ever-increasing loss of weight. No gain in weight was observed with the samples. The results of certain thermal degradation tests for copolymers I I - I V have been tabulated as examples (Table 2). On studying the changes in the weight of the samples under review in relation to degradation time it was found that co]polymers, I, I I I and IV (the heat resistance limit of which is ~140-150 °) withstand prolonged heating at 180-200 °. Copolymers II and V, containing 2,5-dimethylstyrene as second component (heat resistance limit ~ 160-170 °) withstand heating at 200-230 °, with no substantial changes in the weight of the samples. On the basis of the experimental results temperatures were selected at which the effect of stabilizers on the thermal degradation of the copolymers was studied in a second series of tests. For copolymers I, II and IV the temperatures were 210-230 °, for I I I and V, 230-250 °. The tests carried out by the authors showed that the introduction of the stabilizers has no effect on the mechanisms of change in the weight of the samples relative to heating time. In most cases the copolymers containing stabilizers are cappable of withstanding ]prolonged heating at temperatures 30-40 ° higher than in the first series of tests (Table 2). ~Iowever, the action of the stabilizers during thermal degradation of the co]polymers is not equally effective. Thus for copolymer I I only di-n-butyltin maleate and di-nbutyltin dicaprylate were effective: the stabilizers all have the same effect on I and V. It is generally undesirable to introduce more than 3% stabilizer. It was found necessary to increase the amount of the organotin corn]pound to 5 % only in the degradation of copolymer I I I containing the largest amount of fluorine (see Table 1); in this case di-n-butyltin maleate was effective. Regardless of whether stabilizers were used in the tests the following changes occurred in the co]polymers apart from the weight decrease: during heating the samples took on a coloration varying from bright yellow to dark brown, sweated and swelled. In most cases the co]polymers became insoluble after heating and crosslinking was observed (Table 2). In the earlier stages of degradation samples of II and V were subject to crosslinking. The loss of solubility after heating was not ]prevented by changing the stabilizers, as in the second series of tests the copolymers were subject to crosslinking at even earlier stages of degradation (with a weight loss of up to 1%) which may be the result of the higher degradation temperature. In cases where the MWN could be determined for the samples it was found that after heating the molecular weight was reduced. The Figure shows a Grassy diagram of the change in the 1VIWNof co]polymer IV with and without stabilizer during the early period of degradation (prior to loss of solubility). There is a marked reduction in the ~ of co]polymer IV before any appreciable decrease occurs in the weight of the sample, indicating the random breakdown of polymer molecules [4]. The Figure shows that the introduction of the stabilizer does not affect the type of breakdown of the main chain of the co]polymer. The results of analysis for fluorine showed that in the first series of tests
1670
N.S.
GASHTOL'D et al.
TABLE 2. RESULTS OF EXPERIMENTS FOR THERMALDEGRADATIONOF THE OOPOLYMERS Copolymor
Stabilizer content,
Degradation temperature,
% J
II
No stabilizer
II
Di-n-butyltin maleate, 3 %
II
Di-n-butyltin dicaprylate, 3%
II
Di-n-butyltin dilaurate, 3%
V
No stabilizer
V
Di-n-butyltin maleate, 3 % Ditto, 5 ~ Di-n-butyltin dilaurate, 3% Di-n-butyltin dicaprylate, 3 %
V V III
No stabilizer
Ill
Di-n-butyltin maleate, 3%
III
Ditto, 5%
III
Di-n-butyltin dicaprylate, 3%
III
Ditto, 5%
III
Di-n-butyltin dilaurate, 3%
III
Ditto, 5%
* d - - d i s s o l v e s ; x - - d o e s n o t dissolve.
°c 180 200 200 220 220 220 230 250 250 250 250 250 250 230 23O 25O 250 250 250 180 180 200 210 210 210 210 210 180 180 210 210 210 210 210 210 210 210 210 210 210 210 210 210
Heating time, hr 200 2 20 2 4 9 1 1 11 1 11 1 16 0.5 1.5 11 6 9 11 5 12 22 3 6 1 3 6 150 100 1 6 4 20 1 3 1 6 1 3 6 1 3 6
Weight loss,
% 0"10 0"59 0"59 0"49 2"10 15"20 1"05 4"11 - 4.47 3.12 3.20 5"51 7-82 2.37 15-37 0 0 0 0 12'00 13"50 4"10 1 "40 13-38 0.55 1.18 4-44 1-77 5.81 0"66 2.14 1.99 3"20 4.17 16-79 6"10 19"82 1-80 15"30 19.36 1"67 15"30 20"94
Fluorine Solubil. content, ity*
%
23-5
d
19.7
X
17.2
X
20.5
X
11-8 17-8 21.5 18"0 18.1
d X x X X
19.5
X
17.9 22.0 18.5
X
25.2
d
26 "2
X
d 16.8 12-9
d
13.8
d
11"7
d
Thermal degradation of fluorine-containing polymers
1671
fluorine detachment always occurred in the course of thermal degradation. With a rise in temperature the rate of fluorine detachment is increased (Table 2). B y means of control tests acid pairs were de~ected in volatile degradation products. As was prev/ously shown in [1] the stabilizers used by the authors in the degradation of PVC do not alter the nature of structural changes. The marked improvement in the thermal stability of PVC is attributed to the action of organotin compounds as oxidation inhibitors and accepters of the hydrogen chloride t h a t is evolved. I t was therefore of interest to determine whether the fluorine content of samples containing a stabilizer is reduced after degradation. The detachment of fluorine during heating was detected in the second series of tests also, but in cases where the stabilizing effect of organotin additives is obvious the fluorine content of the samples after degradation was much higher t h a n in the case of the copolymers t h a t had been heated without a stabilizer (Table 2). This shows, therefore, t h a t the stabilizers inhibit the removal of fluorine from the samples. Weight/o~, #0 80 80 I
I
100
I
I
eO~-\'-,,\ \ \
\
\
\
\ X
2O
\ \
0
MVN ~ MVNinEt
Grassy diagram for eopolymer IV: Degradation of eopolymer w~thout a stabilizer at 210° (1) and with a stabilizer (3% di-n-butyltin male~te) st 230° (2). With copolymers I, I I I and IV it was possible using the E P R * method to detect in the degraded samples stable radicals similar to those described in [5]. On comparing the E P R spectra obtained in these tests with data in [5], the structures we would assign to these radicals are F
~F
,,,O--cinI
F
~d ~F
~c--6~
* The authors wish to thanl~ _A. G. Boldyrev and V. L. Maksimov for ass/sting w/th these experiments.
1672
N.S. GASHTOL'D et al.
in I I I and V--the same radicals as in I, and in addition H H ~ C--C ~
~
H~C.
CHs H
F F ~ C--C ~ and
~H
~ 2
The nature of the radicals produced in samples I I I and V helps to explain the crosslinking of the copolymers during the thermal degradation. NMI~ spectra of copolymers of fluorostyrenes with styrene are given in [6]. Interpretation of the I~MR spectra of solutions of heated I I I and IV copolymers showed that generally a fluorine atom is detached from the a-carbon atom of fluorostyrene [6]. Similar results were obtained for samples I I I and IV containing stabilizers; although the reduction in the amount of fluorine in the copolymers is much smaller, in these cases also the fluorine is mostly detached from the acarbon of the vinyl group of fluorine-containing units of the copolymer. The authors are most grateful to Ye. V. Kuvshinskii for taking part in the discussion of results. CONCLUSIONS
(1) It has been shown that copolymers of a,fl,fl,-trifluorostyrene (and its T-methyl- and m-methylsubstituted isomers) with styrene and 2,5-dimethylstyrene are capable of withstanding prolonged heating at 180-230 ° (depending on the composition and structure of the copolymers) without undergoing appreciable change in weight. (2) The degradation of all the copolymers under review takes place according to a random law; during thermal degradation there is rapid detachment of fluorine (mainly from the a-carbon atom of the vinyl group) and the crosslinking of samples with CI~3 groups in the benzene ring is observed. (3) Organotin stabilizers generally improve the thermal stability of the copolymers by approximately 30-40 ° without affecting the characteristic breakdown of the polymer chains or the crosslinking of the samples, but acting purely as acceptors. Translated b24 R. J. A. HEI~rDRY
REFERENCES 1. M. N. SHTEDING a n d V. L. KARPOV, Vysokomol. soyed. 4: 1807, 1962 (Not translated in P o l y m e r Sei. U.S.S.R.) 2. A. F. DOKUKINA, M. M. KOTON, Z. A. SMIRNOVA, Ye. I. YEGOROVA, D. A. KOCHESKOV, T. V. TALALAYEVA and G. V. TIiVIOFEYUK, U.S.S.R. Pat. 162964, 1964; Byull. izob., No. 11, 1964 3. A. I. LEBEDEVA, M. M. NIKOLAYEVA and V. A. ORESTOVA, Zh. analit, khim. 16: 469, 1961 4. N. GRASSY, Chemistry of Polymer Degradation Processes, Foreign Lit. Pub. House, 1959
Polymerization kinetics in the presence of substances decomposing to inhibitors 1673 5. V. V. ANTUF'EV, A. F. DOKUKINA, M. P. BOTINOV, Ye. V. SUNTSOV and A. G. BOLDYREV, Vysokomol. soyed. 7: 380, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 3, 411, 1963) 6. V. L. MAKSIMOV, M. P. BOTINOV and A. F. DOKUKINA, Vysokomol. soyed. 8: 1117, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 6, 1230, 1966)
KINETICS OF POLYMERIZATION IN THE PRESENCE OF SUBSTANCES DECOMPOSING TO INHIBITORS* L. I. ]V[AKHONINA, V. A. SEOHKOVSKAYA, G. P. GLADYSHEV, G. V. KOROLEV
and S. 1%. 1%AFIKOV A~liated Branch of the Institute of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 18 June 1966)
lVfA~rr substances (hydrazine derivatives, nitroso compounds, complexes, salts and so on) are capable of thermal decomposition to form products that are radical chain inhibitors (1~0, 02, 1VH3, radicals of low activity, etc.). Moreover, if the energy of the dissociating bond is within the limits of 30-40 kcal/mole, the thermal decomposition rates will be commensurate with rates of the initiation of radical chain polymerization by ordinary initiators (peroxides, azo compounds). By introducing into polymerizing systems substances (A) capable of decomposing to inhibitors (X) it may be possible to develop new methods of controlling polymerization compared with the introduction of a ready-made inhibitor X. I n this paper a study is made of the polymerization kinetics of methyl mcthacrylate (MMA) in the presence of N-nitrosodiphcnylamine (~TFA) used as A. It was shown [1] that at temperatures above 50 ° :N-FA decomposes to form NO and a low-activity diphenylnitroxide radical. Both these products are efficient inhibitors of radical chain polymerization [2]. The NFA molecules themselves are relatively weak inhibitors of the polymerization process. Some aspects of polymerization in the presence of :NFA additives were studied by Tiidesch [3], using styrene as an example. It was shown that with a rise in temperature a marked change occurs in the stoichiometric coefficient of inhibition by NFA which agrees with the mechanism that includes two types of inhibition by :NF2r: by the actual NFA molecules, and the thermal decomposition products of ~ F A . The contribution of the latter is increased markedly with a temperature rise, on account of the high activation energy of the thermal decomposition of NFA ( ~ 30 kcal/mole). * Vysokomol soyed. A9: No. 7, 1494-1498, 1967.
1667
REFERENCES
1. J. MORRISON, W. CAMPBELL and O. MAASS, Canad. J. Res. 18B: 168, 1940; OKAMURA Naturwissenschaften 21: 328, 1933 2. N. V. MIKHAILOV and E. Z. FAINBERG, Koll. Zh. 18: 315, 1956 3. W. REESS, J. Text. Inst. 39: T351, 1948 4. J. GUTHRIE, J. Text. Inst. 40: T489, 1949 5. H. MARK, Quot. from Bil'meier, Introduction to Polymer Chemistry and Technology, 27, 1961 6. W. MORTON and J. HEARLE, Physical Properties of Textile Fibres (monograph), Manchester, Butterworths Textile Institute, 179, 1962 7. J. J. MANN and H. J. MARINANN, Trans. Faraday Soc. 52: 481, 1956
ORGANOTIN COMPOUNDS AS STABILIZERS OF THERMAL DEGRADATION OF FLUORINE-CONTAINING POLYMERS N. S. GASHTOL'D, A. F. DOKIrKINA, K. A. KOCHESKKOV and T. V. TAY~AT,AYEVA M. I. KaUnin Polytechnical Institute, Leningrad (/~eceived 17 June 1966) S~VV.RAL reports have appeared in the literature [1] regarding the stabilizing effect of organotin compounds which improve the heat resistance, thermal stability and fastness to light of polymeric materials based on polyvinylchioride. The present report is based on stabilizers of this t y p e and the thermal degradation of fluorine-containing copolymers of a,fl,fl-trifluorostyrene (and its p-methyl- and m-methylsubstituted isomers) with styrene and 2,5-dimethylstyrene. The substances investigated were five copolymers differing as to their fluorine content (18 to 2 5 ~ ) and as to the number of methyl groups in the benzene rings (Table 1, [2]). The stabilizers were: di-n-butyltin maleate, di-n-butyltin dicaprylate and di-n-butyltin dilaurate. Samples of the copolymers containing no stabilizer were investigated, as well as mechanical mixtures of the polymers and organotin compounds listed above. The stabilizer content of the copolymers varied from 3 to 50/o. The degradation of two types of sample was investigated: powders and press-moulded discs 2-4 m m thick and 8-10 mm in diameter. The estimated amount of thermal degradation was based on: the weight loss, measurement of the exterior of the sample, the fluorine content [3], solubility, and changes in the maximum viscosity number (MV~). Nuclear magnetic resonance and electron paramagnetic resonance spectra were recorded for several of the thermally treated samples, and interpreted. * Vysokomol. soyed. Ag: No. 7, 1489-1493, 1967.
1668
N . S. GASHTOL'D e$ a/.
The samples were heated in air in a flask (the control samples were vacuumheated) fitted with an electric heater: measurement and control of the temperature was eifected b y means of an automatic electronic self-recording d.c. bridge (type E1VII)-ll2) using a platinum resistance thermometer situated inside the heater. The temperature control was accurate to ~:0.5 °. The temperature of the sample was determined with an iV[S-I-01 device the resistance thermometer of which was in the flask below a support with the sample. The MVN values were found b y viscometry at 20.0-4-0.1 °. using an Ubbelohde viscometer and solutions of the polymers in benzene. The degradation temperatures were selected as follows: the lower limit was 40 to 50 ° higher t h a n the heat resistance of the copolymer (found b y I R pyrolysis) and the upper limit was determined from the abrupt change in the weight of the samples. DISCUSSION OF RESULTS
Two series of tests were carried out during investigation of the thermal degradation of fluorine-containing copolymers: with and without stabilizers. In the first series of tests samples of copolymers I I - Y (Table 1) were kept for different times (from 0.5 to 22 hr; for sample I I I up to 200 hr) at temperatures of 180-230 °. TABLE 1. COMPOSITIO~ AND PROPERTIES OF COPOLYMERS UI~DER REVIEW [2]
Copolymers
I II III
IV V
~.,fl,fl-Trifluorostyrene + styrene a,fl,fl-Trifluor-]- 2,5-diinethylstyrene 3-Methyl-~,fl,fl-trifluorostyrene ~-styrene 4-Methyl-~,fl,fl-trifluorostyrene ~styrene 4 -Methyl-a,fl,]Ltrifluorostyrene -~ 2,5-dimethylstyrene
Composition of Heat recopolymer, sistance MVN mole % by IR fluorine pyro-I 20° corn- styrene lysis,°C ~ ponent
Fluorine content of eopolymer, ~/o
39"8 63.6
60.2 36.4
148 164
2"9 0-5
18.1 23.6
74.2
25-8
139
0-2
27.4
54.3
45.7
148
0.5
22-0
69.4
30.6
171
0.6
24.7
The change in weight in relation to heating time was approximately the same for all the copolymers and was unaffected b y the form of the sample under investigation (powder or disc), A t temperatures 40 ° higher than their heat resistance limit the copolymers either suffered a weight loss of 0.5 to 2% during the initial period, after which their weight remained constant, or else there was a gradual b u t very slow change in their weight, the total change in 12-20 h r being 3 to 4%. I f the temperature is raised b y a further 20-50 ° rapid degradation of
Thermal degradation of fluorine-containing polymers
1669
the sample is observed, with ever-increasing loss of weight. No gain in weight was observed with the samples. The results of certain thermal degradation tests for copolymers I I - I V have been tabulated as examples (Table 2). On studying the changes in the weight of the samples under review in relation to degradation time it was found that co]polymers, I, I I I and IV (the heat resistance limit of which is ~140-150 °) withstand prolonged heating at 180-200 °. Copolymers II and V, containing 2,5-dimethylstyrene as second component (heat resistance limit ~ 160-170 °) withstand heating at 200-230 °, with no substantial changes in the weight of the samples. On the basis of the experimental results temperatures were selected at which the effect of stabilizers on the thermal degradation of the copolymers was studied in a second series of tests. For copolymers I, II and IV the temperatures were 210-230 °, for I I I and V, 230-250 °. The tests carried out by the authors showed that the introduction of the stabilizers has no effect on the mechanisms of change in the weight of the samples relative to heating time. In most cases the copolymers containing stabilizers are cappable of withstanding ]prolonged heating at temperatures 30-40 ° higher than in the first series of tests (Table 2). ~Iowever, the action of the stabilizers during thermal degradation of the co]polymers is not equally effective. Thus for copolymer I I only di-n-butyltin maleate and di-nbutyltin dicaprylate were effective: the stabilizers all have the same effect on I and V. It is generally undesirable to introduce more than 3% stabilizer. It was found necessary to increase the amount of the organotin corn]pound to 5 % only in the degradation of copolymer I I I containing the largest amount of fluorine (see Table 1); in this case di-n-butyltin maleate was effective. Regardless of whether stabilizers were used in the tests the following changes occurred in the co]polymers apart from the weight decrease: during heating the samples took on a coloration varying from bright yellow to dark brown, sweated and swelled. In most cases the co]polymers became insoluble after heating and crosslinking was observed (Table 2). In the earlier stages of degradation samples of II and V were subject to crosslinking. The loss of solubility after heating was not ]prevented by changing the stabilizers, as in the second series of tests the copolymers were subject to crosslinking at even earlier stages of degradation (with a weight loss of up to 1%) which may be the result of the higher degradation temperature. In cases where the MWN could be determined for the samples it was found that after heating the molecular weight was reduced. The Figure shows a Grassy diagram of the change in the 1VIWNof co]polymer IV with and without stabilizer during the early period of degradation (prior to loss of solubility). There is a marked reduction in the ~ of co]polymer IV before any appreciable decrease occurs in the weight of the sample, indicating the random breakdown of polymer molecules [4]. The Figure shows that the introduction of the stabilizer does not affect the type of breakdown of the main chain of the co]polymer. The results of analysis for fluorine showed that in the first series of tests
1670
N.S.
GASHTOL'D et al.
TABLE 2. RESULTS OF EXPERIMENTS FOR THERMALDEGRADATIONOF THE OOPOLYMERS Copolymor
Stabilizer content,
Degradation temperature,
% J
II
No stabilizer
II
Di-n-butyltin maleate, 3 %
II
Di-n-butyltin dicaprylate, 3%
II
Di-n-butyltin dilaurate, 3%
V
No stabilizer
V
Di-n-butyltin maleate, 3 % Ditto, 5 ~ Di-n-butyltin dilaurate, 3% Di-n-butyltin dicaprylate, 3 %
V V III
No stabilizer
Ill
Di-n-butyltin maleate, 3%
III
Ditto, 5%
III
Di-n-butyltin dicaprylate, 3%
III
Ditto, 5%
III
Di-n-butyltin dilaurate, 3%
III
Ditto, 5%
* d - - d i s s o l v e s ; x - - d o e s n o t dissolve.
°c 180 200 200 220 220 220 230 250 250 250 250 250 250 230 23O 25O 250 250 250 180 180 200 210 210 210 210 210 180 180 210 210 210 210 210 210 210 210 210 210 210 210 210 210
Heating time, hr 200 2 20 2 4 9 1 1 11 1 11 1 16 0.5 1.5 11 6 9 11 5 12 22 3 6 1 3 6 150 100 1 6 4 20 1 3 1 6 1 3 6 1 3 6
Weight loss,
% 0"10 0"59 0"59 0"49 2"10 15"20 1"05 4"11 - 4.47 3.12 3.20 5"51 7-82 2.37 15-37 0 0 0 0 12'00 13"50 4"10 1 "40 13-38 0.55 1.18 4-44 1-77 5.81 0"66 2.14 1.99 3"20 4.17 16-79 6"10 19"82 1-80 15"30 19.36 1"67 15"30 20"94
Fluorine Solubil. content, ity*
%
23-5
d
19.7
X
17.2
X
20.5
X
11-8 17-8 21.5 18"0 18.1
d X x X X
19.5
X
17.9 22.0 18.5
X
25.2
d
26 "2
X
d 16.8 12-9
d
13.8
d
11"7
d
Thermal degradation of fluorine-containing polymers
1671
fluorine detachment always occurred in the course of thermal degradation. With a rise in temperature the rate of fluorine detachment is increased (Table 2). B y means of control tests acid pairs were de~ected in volatile degradation products. As was prev/ously shown in [1] the stabilizers used by the authors in the degradation of PVC do not alter the nature of structural changes. The marked improvement in the thermal stability of PVC is attributed to the action of organotin compounds as oxidation inhibitors and accepters of the hydrogen chloride t h a t is evolved. I t was therefore of interest to determine whether the fluorine content of samples containing a stabilizer is reduced after degradation. The detachment of fluorine during heating was detected in the second series of tests also, but in cases where the stabilizing effect of organotin additives is obvious the fluorine content of the samples after degradation was much higher t h a n in the case of the copolymers t h a t had been heated without a stabilizer (Table 2). This shows, therefore, t h a t the stabilizers inhibit the removal of fluorine from the samples. Weight/o~, #0 80 80 I
I
100
I
I
eO~-\'-,,\ \ \
\
\
\
\ X
2O
\ \
0
MVN ~ MVNinEt
Grassy diagram for eopolymer IV: Degradation of eopolymer w~thout a stabilizer at 210° (1) and with a stabilizer (3% di-n-butyltin male~te) st 230° (2). With copolymers I, I I I and IV it was possible using the E P R * method to detect in the degraded samples stable radicals similar to those described in [5]. On comparing the E P R spectra obtained in these tests with data in [5], the structures we would assign to these radicals are F
~F
,,,O--cinI
F
~d ~F
~c--6~
* The authors wish to thanl~ _A. G. Boldyrev and V. L. Maksimov for ass/sting w/th these experiments.
1672
N.S. GASHTOL'D et al.
in I I I and V--the same radicals as in I, and in addition H H ~ C--C ~
~
H~C.
CHs H
F F ~ C--C ~ and
~H
~ 2
The nature of the radicals produced in samples I I I and V helps to explain the crosslinking of the copolymers during the thermal degradation. NMI~ spectra of copolymers of fluorostyrenes with styrene are given in [6]. Interpretation of the I~MR spectra of solutions of heated I I I and IV copolymers showed that generally a fluorine atom is detached from the a-carbon atom of fluorostyrene [6]. Similar results were obtained for samples I I I and IV containing stabilizers; although the reduction in the amount of fluorine in the copolymers is much smaller, in these cases also the fluorine is mostly detached from the acarbon of the vinyl group of fluorine-containing units of the copolymer. The authors are most grateful to Ye. V. Kuvshinskii for taking part in the discussion of results. CONCLUSIONS
(1) It has been shown that copolymers of a,fl,fl,-trifluorostyrene (and its T-methyl- and m-methylsubstituted isomers) with styrene and 2,5-dimethylstyrene are capable of withstanding prolonged heating at 180-230 ° (depending on the composition and structure of the copolymers) without undergoing appreciable change in weight. (2) The degradation of all the copolymers under review takes place according to a random law; during thermal degradation there is rapid detachment of fluorine (mainly from the a-carbon atom of the vinyl group) and the crosslinking of samples with CI~3 groups in the benzene ring is observed. (3) Organotin stabilizers generally improve the thermal stability of the copolymers by approximately 30-40 ° without affecting the characteristic breakdown of the polymer chains or the crosslinking of the samples, but acting purely as acceptors. Translated b24 R. J. A. HEI~rDRY
REFERENCES 1. M. N. SHTEDING a n d V. L. KARPOV, Vysokomol. soyed. 4: 1807, 1962 (Not translated in P o l y m e r Sei. U.S.S.R.) 2. A. F. DOKUKINA, M. M. KOTON, Z. A. SMIRNOVA, Ye. I. YEGOROVA, D. A. KOCHESKOV, T. V. TALALAYEVA and G. V. TIiVIOFEYUK, U.S.S.R. Pat. 162964, 1964; Byull. izob., No. 11, 1964 3. A. I. LEBEDEVA, M. M. NIKOLAYEVA and V. A. ORESTOVA, Zh. analit, khim. 16: 469, 1961 4. N. GRASSY, Chemistry of Polymer Degradation Processes, Foreign Lit. Pub. House, 1959
Polymerization kinetics in the presence of substances decomposing to inhibitors 1673 5. V. V. ANTUF'EV, A. F. DOKUKINA, M. P. BOTINOV, Ye. V. SUNTSOV and A. G. BOLDYREV, Vysokomol. soyed. 7: 380, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 3, 411, 1963) 6. V. L. MAKSIMOV, M. P. BOTINOV and A. F. DOKUKINA, Vysokomol. soyed. 8: 1117, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 6, 1230, 1966)
KINETICS OF POLYMERIZATION IN THE PRESENCE OF SUBSTANCES DECOMPOSING TO INHIBITORS* L. I. ]V[AKHONINA, V. A. SEOHKOVSKAYA, G. P. GLADYSHEV, G. V. KOROLEV
and S. 1%. 1%AFIKOV A~liated Branch of the Institute of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 18 June 1966)
lVfA~rr substances (hydrazine derivatives, nitroso compounds, complexes, salts and so on) are capable of thermal decomposition to form products that are radical chain inhibitors (1~0, 02, 1VH3, radicals of low activity, etc.). Moreover, if the energy of the dissociating bond is within the limits of 30-40 kcal/mole, the thermal decomposition rates will be commensurate with rates of the initiation of radical chain polymerization by ordinary initiators (peroxides, azo compounds). By introducing into polymerizing systems substances (A) capable of decomposing to inhibitors (X) it may be possible to develop new methods of controlling polymerization compared with the introduction of a ready-made inhibitor X. I n this paper a study is made of the polymerization kinetics of methyl mcthacrylate (MMA) in the presence of N-nitrosodiphcnylamine (~TFA) used as A. It was shown [1] that at temperatures above 50 ° :N-FA decomposes to form NO and a low-activity diphenylnitroxide radical. Both these products are efficient inhibitors of radical chain polymerization [2]. The NFA molecules themselves are relatively weak inhibitors of the polymerization process. Some aspects of polymerization in the presence of :NFA additives were studied by Tiidesch [3], using styrene as an example. It was shown that with a rise in temperature a marked change occurs in the stoichiometric coefficient of inhibition by NFA which agrees with the mechanism that includes two types of inhibition by :NF2r: by the actual NFA molecules, and the thermal decomposition products of ~ F A . The contribution of the latter is increased markedly with a temperature rise, on account of the high activation energy of the thermal decomposition of NFA ( ~ 30 kcal/mole). * Vysokomol soyed. A9: No. 7, 1494-1498, 1967.