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The structure and thermal stability of copolymers of 3-methylbutene-1 and vinylcyclohexane
THE STRUCTURE AND THERMAL STABILITY OF COPOLYMERS OF 3-METHYLBUTENE-1 AND VINYLCYCLOHEXANE* YU. YA. GOZ'DFARR, N. A. NECHITA.Vf,O, YU. V. KISSIN, Yu. V. NOVODERZErgr~ a n d 1~. A. DZYUBI~A A. V. Topchiyev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 21 August 1975) The copolymer of 3-methylbutene-1 (MB) and vinylcyclohexane (VCH) has been investigated by methods of IR spectroscopy, DTA and X-ray structural analysis. The results show that the structure of MB-VCtt copolymers is statistical in charactor. In the light of DTA results temperature intervals of decomposition were dotermined for copolymers with varying contents of MB and VCt[ units, heating the copolymers in argon and in air, and in the presence of some stabilizers. ISOTACTIC h o m o p o l y m e r s o f 3 - m e t h y l b u t e n e - 1 (]VLB) a n d v i n y l c y c l o h e x a n o (VCH) are highly crystalline p o l y m e r s with melting points of 300 a n d 380 ° respectively, which makes t h e processing of MB a n d VCIt e x t r e m e l y difficult. F r o m a s t r u c t u r a l - c h e m i c a l s t a n d p o i n t the similarity o f these two m o n o m e r s is v e r y marked; b o t h h a v e b r a n c h i n g alongside t h e double bond. This a p p a r e n t l y accounts for t h e i r r e l a t i v e l y low r e a c t i v i t y in p o l y m e r i z a t i o n processes [1]. I t was to be e x p e c t e d t h a t copolymers of MB a n d VCH would be superior t o P M B a n d P V C H as regards t h e r m a l stability a n d processing ability. I n the work r e p o r t e d below different physical m e t h o d s were used in s t r u c t u r a l investigations of M B - V P G copolymers w i t h V C H c o n t e n t s o f 16, 50, 73 a n d 95%. W e also p r e s e n t results of our s t u d y of t h e b e h a v i o u r of these copolymers in t h e r mal a n d t h e r m o o x i d a t i v e d e g r a d a t i o n processes. These findings are c o m p a r e d w i t h analogous results for eopolymers of 4 - m e t h y l p e n t e n e - 1 (MP) a n d VCH, t h e struct u r e of which was the subject of t h e earlier investigations r e p o r t e d in [2]. The IR spectra of the eopolymers and homopolymers of MB and VCH were recorded on a UR-10 spectrophotometer (the samples for photographing were prepared by hot moulding). The copolymer compositions were determined by IR analysis based on the intensity ratio of the band at 138~5 cm -1 (one of the doublet components relating to symmetrical deformation vibrations of CH3 in MB units) and 892 cm -1 (vibrations of the eyclohexano ring [2]). Since weak absorption of VCH units also occurs at 1385 cm-L the optical densities of the bands are expressed as MB VCH D13ss~[KlasSCMB-~Klas5 "(1--CMB)]l D 891 __ - - ~~/'VCH 892
(1--CMB)
* Vysokomol. soyed. AI8: ~o. 8, 1813-1818, 1976. 2075
g,
(1) (2)
2076
Y ~ . YA. GOL'DF&RB et a~.
where K are the absorption coefficients of the respective bands, / is the film width, and c - is the mole fraction of biB in the copolymer. T h e calibration curve for measurement of the copolymer compositions is expressed as VCH VCE[ MB V C H Dlsss/Dsss = Klsss /Km + (K18sdKm ) Ct,B/(1-- CMB) ,
/(MS/wVCH_ where ]FffVCH//(VCH--o'9"(from the P¥CH spectrum), and __lsss,_+m --_~-n v (calculated from the values of the absorption coefficients of the appropriate bands in the spectra of t h e homopolymers). The spectra of mixtures of the homopolymers were used to verify the calibration curve. A URS-50IK apparatus was used for recording X-ray diffraction patterns of the copolymers and homopolymers of MB and ~7CH (powders prepared in the course of copolymerization); the I)TA curves were plotted with the aid of the Paulik-Paulik-Erden derivatograph. Calcined Al~Os was Used as the standard. The rate of heating was 3 deg/min; each test sample weighed 0.150 g.
Structure of the M B - V C H co2aolymers. The copolymerization constants for MB and VCH (r 1 and rs respectively) based on the Fineman-Ross method [3] w e r e 1.02 and 0.98 respectively.. The fact t h a t the constants are close to u n i t y means t h a t the reactivities of the two monomers are practically identical, which, as was said above, is due to their structural similarity. Judging by the p r o d u c t of rlr 2, the copolymerization of MB with VCH would seem to take place with formation of copolymers t h a t are statistical in character. On going from homopolymers of MB and VCH to MB-VCH copolymers, one finds changes appearing in several of the physical characteristics of the latter. One normally finds t h a t bands in the I R spectra of olefin copolymers t h a t are most sensitive to the distribution of monomer units are those t h a t are sensitive to stereospecificity in the spectra of the homopolymers [1]. Among the bands most sensitive to stereospecificity in the PMB spectrum is t h a t at 778 cm -1 pertaining to the vibrations of large isotactic blocks. The addition of as little as ~ 10% o f VCH units into the eopolymer already leads to a ~ 2 fold reduction in the relative intensity of the band in question (the "isotacticity" index for MB units in t h e copolymer is 48% [4]), while the band at 778 cm -1 disappears entirely from t h e spectra of copolymers with > 2 0 % contents of VCH units. Behaviour of this t y p e on the part of stereospecificity bands in the spectra of the copolymers is characteristic of copolymers with structures t h a t are statistical in character. A comparison of the I R spectra of MB-VCH copolymers of varying composition revealed a further band t h a t is sensitive to the distribution of MB units, i,e. the band at 1118 cm -1. The optical density of the latter band is described by t h e expression MB
Dms---:KlllSCMB~cn+ll,
(3)
where ~.+1 is the fraction of MB units in the total number of blocks exceeding n units in length. Combining expressions (1)-(3) we obtain the following expression for the relative intensity of the 1118 cm-1 band normalized for the total number of biB units
Copolymers of 3-methylbutene.1 and vinyleyclohexane
2077
in t h e c o p o l y m e r
DM8
K~liis
(DI,,5--0"2Ds,=) : K~B5 = K . + ,
The value of =~nlS/==za85, UMB / u = s measured in the PM-B spectra, is 0.22. Figure 1 shows plots of [D1zts/(Dzass-O'2Dag=)/0.22 (A) a n d t h e calculated plots o f K#+l vs. c o p o l y m e r composition, s t a r t i n g w i t h values for rzrs= 1 given in [1]. On c o m p a r i n g t h e e x p e r i m e n t a l a n d theoretical d a t a it can be seen t h a t for t h e b a n d a t 1118 cm -1 n'-' 6-7.
A 1.0
b
oe /00
\\ ,
r,
i
60
----
~Z?
C M s , mole %
FIO. 1
I zo
I I0 FIG. 2
28"
FiG. 1. Relative intensity of the band at 1118 cm -1 in the IR spectra of the MB-YCH c o ° polymers vs. copolymer composition (see text): points--experimental data; the plots o f K6 and K7 are theoretical curves FIO. 2. Diffraction patterns of PMB (1), PVCH (5), and MB-VCH copolymers with VCH contents of 16 (2), 73 (3) and 95% (4). I t was d e m o n s t r a t e d in [2] t h a t t h e distribution of V C H units in V C H co. p o l y m e r s m a y be d e t e r m i n e d f r o m the i n t e n s i t y ratio o f c o m p o n e n t s of the doublet, a t 892-884 cm -1 characterizing v i b r a t i o n s of t h e cyclohexane ring. The i n t e n s i t y o f the 892 cm -1 b a n d in t h e P V C H s p e c t r u m exceeds t h a t of t h e b a n d at 884 c m -1, while t h e reverse is o b s e r v e d in the spectra o f t h e copolymers.
"2078
Y ~ . YA. (~OL'DFAI~B e~ a[.
A similar phenomenon is likewise found in the spectra of the MB-VCH co:polymers: in the PVCH spectrum D89~/Dss~~ 1.2, with an 84% MB content it is ~ 1-0, and ~0.6 for a 90~/o MB content. Figure 2 shows the diffraction patterns of PMB and PVCH powders and of t h e MB-VCH copolymers. The homopolymerization of MB results in a highly crystalline product. At the same time the homopolymerization of VCH results in a polymer that is only slightly crystalline in view of the higher glass transition of PVCH compared with the polymerization temperature [5]. I t can be seen from Fig. 2 that the addition of ~ 16% of VCH to the eopolymer is accompanied by practically complete amorphization of the product, which agrees with structure o f a statistical character envisaged for MB-VCH eopolymers. The broad reflection appearing in the region of 2 ~ 8-10 ° in the diffraction patterns of the copolymers is apparently attributable to reflections relating to planes parallel to the polymer chain axes (the corresponding reflection in the diffraction pattern of PMB is that with 2~--~10.4 ° corresponding to a reflection from the (100)* plane. As the VCH content in the eopolymers rises, the latter peak is displaced towards smaller angles (for PVCH 2 ~ 8.3 °) as a result of increased interehain spacings due to replacement of MB units by the more bulky VCH units. The DTA curves for PMB, PVCH and the MV-VCH eopolymers displayed in Fig. 3 were plotted while heating the samples in an argon atmosphere. The melting peak for PMB is situated at 300 °. The insertion of ~ 1 6 % of ¥ C H into the polymer brings the melting point down to ~275 °, and results in a m a r k e d diminution of the area under the melting peak, and in a widening of t h e peak, while in the case of the copolymer with a VCH content of ~50%, t h e melting peak is virtually absent. These changes are all in agreement with inferences that m a y be drawn from the Flory theory in regard to the melting of defective crystalline polymers and copolymers [7], according to which it appears that for copolymers with rl, r2-----1, the relation of the melting point to t h e content of a given component is described by the expression
1/T~ p - 1/T h°m°p• --(R/AH u) ln cM,
(4)
where R is the gas constant, AHu is the heat of melting for the homopolymer calculating for the monomer unit, and vM is the number of units of the given m o n o m e r in the copolymer. O n further increasing the VCH content in the eopolymer a weak peak begins t o appear on DTA curves for the melting of VCH crystalline blocks: with 73% VCH at ~290 °, 95°/o ~340 ° (for PVCH Tm----375-380 ° [5]). I t can be seen from Figs. 2 and 3 t h a t t h e crystallinity of VCH blocks in the copolymers, like the ~rystallinity of PVCH itself, is extremely low immediately after polymerization, s l t h o u g h as the number of VCtt blocks decreases reductions in the melting points e f t h e latter can be detected on the DTA curves, which is likewise consistent * Assignment of the reflection is based on the data in [6].
Copolymers of 3-methylbutene-l and vinylcyc]ohcxane
2079
with what m a y be deduced from Flory's theory for statistical copolymers. Using formula (4) the molar heats of melting determined for PlVI~ and PVOH from the melting point data amount to ~4400 and 3300 cal/mole. I n view of the total amount of data based on I R and X-ray analysis and DTA it can therefore be s~id that the MB-VCH copolymers have statistical structures. This is also borne out by the value of rlr =for the pair of monomers in question. LIT
!
I.
tO0
I
JO0
FIG. 3
I v
I
500 T,°C
36O
~ Fro. 4
0,0 T,~
~FiG. 3. DTA curves of PMB (1), PVCH (6), MB-VCH copolymers with VCH contents of 16 (2), 50 (3), 73 (4) and 95% (5). Fro. 4. Weight loss of polymers vs. temperature during heating in argon: 1-3, 5--MB-VCH copolymers (VCH content--16, 50, 73 and 95 mole ~/o respectively); 4--PMB; 6--PVCH. Thermal degradation of P M B and of M B - F C H co,polymers. With the aid of the derivatograms (DTG curves) the temperature intervals of decomposition during heating in argon were determined for PMB and M:B-VCH copolymers. The thermal degradation of PMB takes place over the range 360-450 ° (Fig. 3). Using the procedures outlined in Refs. [8, 9] we c~Iculated the average value of the activation energy E~ for the thermal degradation of PMB, and obtained Es----50 kcal/mole (360-400°). The thermal degradation of PVCH and poly-4methylpentene-1 (PMP) was investigated in papers [10, 11]; it was found t h a t PVCH and PMP decompose in the intervals 390-460 and 350-420 ° respectively; the respective values of E a are 56.5 and 54 kcal/mole. The thermal degradation data for the MB-VCH copolymers are displayed in Figs. 3 and 4. The MB-VCH copolymers with VCH units contents of 16, 50 and 73% (curves 1-3 in Fig. 4) have lower heat stability values than the homo-
2080
YU. YA. ~)L'DFARB 6~ ~ .
polymers (curves d, 6). The heat stability of the copolymer containing 95% VOH occupies an intermediate position between PMB and PVCH. It seems that there are two possible factors that could account for the lower heat stability of the copolymers compared with the homopolymers. The incorporation of foreign units, even quite stable one~ (VCH), into the homopolymer could lead to lower bond energy affecting units adjacent to VCH units, thereby facilitating degradation processes. Moreover, the insertion of foreign units will certainly cause disruption of short-range order in polymer melts, which will be another factor favouring degradation processes. /: G
z
•
I
200
II
2O0
¢00
600
I
2oo
~oo 7;, °c 8oo
FIG. 5. DTO (1), DTA (2) and TO (3) curves for PMB (a) and MB-~CCH (b) copolymers (50o//oVCH) during heating in air.
Thermooxidative degradation of MB-VCH copolymers. Derivatograms were recorded during the heating of PMB and MB-VCH copolymers in air. Figure 5 shows, as an example, the derivatograms of PMB and of the MB-VCH copolymer containing 50% VCH. In the light of the DTG and DTA curves one can identify the main stages in the decomposition of the PMB and the MB-VCtt copolymers: the first stage for PMB is at 170-260 °, the second at 260-380 ° and the third at 380-450°; the respective intervals for the copolymer are 200-260, 260-340 and 340-440 °. The first stage corresponds to thermooxidative degradation of the original polymeric hydrocarbons, and takes place via the formation and subsequent decomposition of hydroperoxides; it is accompanied by chain scission, and by the accumulation of oxygen-containing groups in the polymer. The gaseous degradation products released during this stage of the degradation of poIyolefins (water, aldehydes, ketones) contain relatively few 0 atoms, while carbonyl and carboxyl groups appear in the polymer, which means that there
Copolymers of 3-methylbuterm. 1 and viny|cyclohcxane
208I
is altogether no reduction in the weight of products (in the initial stages of oxidation it may even rise slightly (Fig. 5)). The reaction heat for PMB based on the area of the peak was found to be 350 cal/g. Since MB units and VCH units have each two vieinal tertiary H atoms, there is little relationship between the rates of processes of oxidative degradation of the copolymers and their compositions: with VCH contents in the range of 16-95 ~o there is practically no change in the temperature of the onset of oxidation (200--205°). In the second stage of decomposition rapid liberation of volatile products of high molecular weight takes place in the case of the PMB and the MB-VCH copolymer, and polyconjugated systems are formed. The third stage of thermooxidative degradation is characterized by reactions of rapid depletion of oxygencontaining carbonized products, and ends with practically complete conversion of the polymeric residue to gaseous products. Each monomer unit in the MP-VCH copolymers likewise contains two tertiary H atoms, and processes of thermooxidative degradation of these products are similarly practically independent of their composition: the onset of oxidation takes place at 190 ° [11]. The development of thermooxidative degradation of the studied products may be retarted through the introduction of antioxidants. Thus, whereas th~ onset of oxidation appears at 170 ° for unstabilized PMB, the introduction of 1%, of 2,6-ditert.butyl-4-ethyloleatophenol (Irganox 1076) raises the temperature to 210°; it is raised to 255 ° by phenyl-fl-naphthylamine, and to 265 ° by 2,2methylene-bis-4-methyl-6-tert.butylphenol (antioxidant 2246) or diphenyl-pphenylenediamine (the heating rate for the sample being 3 deg/min). Translated by R. J. A. HENDRY REFERENCES
1. Yu. V. KISSIN, Advances Polymer Sci. 15: 82, 1974 2. KHO UILEM, Yu. V. KISSIN, Yu. Ya. GOLDFARB and B. A. KRENTSEL, VysokomoL soyed. 14A: 2229, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 10, 2609, 1972) 3. M. FINEMAN and S. O. ROSS, J. Polymer Sci. 5: 269, 1950 4. Yu. V. KISSIN, Yu. Ira. GOLDFARB, Yu. V. NOVODERZHKIN and V. A. KRENTSEL,. Vysokomol. soycd. B18: 167, 1976 (Not t l a n s l a t e d in Polymer Sci. U.S.S.R.) 5. V. I. KLEINER, Dissertation, 1969 6. G. NATTA, P. CORRADINI and W. B . ~ S I , Rend. Accad. Nazl. Lincei, seric V I I I 19: 404, 1955 7. P. J. FLORY, Trans. F a r a d a y Soc. 51: 484, 1955 8. Z. REICH, Makromolek. Chem. 105: 233, 1967 9. G. O. PILOYAN, Vvedeniye v teoriyu termicheskogo analiza (Introduction to the theory of thermal analysis). Izd. "Mir", p. 148, 1968 10. V. I. KLEINER, N. A. NECHITAILO and L. L. STOTSKAYA, Plast. massy, 1~o. 11, 48, 1971 11. KHO UILEM, N. A. NECHITAILO, Yu. Ya. GOLDFARB, G. P. AFANASOVA and B. A . KRENTSEL, Plast. massy, No. 3, 57, 1972 \
(Received 21 August 1975) The copolymer of 3-methylbutene-1 (MB) and vinylcyclohexane (VCH) has been investigated by methods of IR spectroscopy, DTA and X-ray structural analysis. The results show that the structure of MB-VCtt copolymers is statistical in charactor. In the light of DTA results temperature intervals of decomposition were dotermined for copolymers with varying contents of MB and VCt[ units, heating the copolymers in argon and in air, and in the presence of some stabilizers. ISOTACTIC h o m o p o l y m e r s o f 3 - m e t h y l b u t e n e - 1 (]VLB) a n d v i n y l c y c l o h e x a n o (VCH) are highly crystalline p o l y m e r s with melting points of 300 a n d 380 ° respectively, which makes t h e processing of MB a n d VCIt e x t r e m e l y difficult. F r o m a s t r u c t u r a l - c h e m i c a l s t a n d p o i n t the similarity o f these two m o n o m e r s is v e r y marked; b o t h h a v e b r a n c h i n g alongside t h e double bond. This a p p a r e n t l y accounts for t h e i r r e l a t i v e l y low r e a c t i v i t y in p o l y m e r i z a t i o n processes [1]. I t was to be e x p e c t e d t h a t copolymers of MB a n d VCH would be superior t o P M B a n d P V C H as regards t h e r m a l stability a n d processing ability. I n the work r e p o r t e d below different physical m e t h o d s were used in s t r u c t u r a l investigations of M B - V P G copolymers w i t h V C H c o n t e n t s o f 16, 50, 73 a n d 95%. W e also p r e s e n t results of our s t u d y of t h e b e h a v i o u r of these copolymers in t h e r mal a n d t h e r m o o x i d a t i v e d e g r a d a t i o n processes. These findings are c o m p a r e d w i t h analogous results for eopolymers of 4 - m e t h y l p e n t e n e - 1 (MP) a n d VCH, t h e struct u r e of which was the subject of t h e earlier investigations r e p o r t e d in [2]. The IR spectra of the eopolymers and homopolymers of MB and VCH were recorded on a UR-10 spectrophotometer (the samples for photographing were prepared by hot moulding). The copolymer compositions were determined by IR analysis based on the intensity ratio of the band at 138~5 cm -1 (one of the doublet components relating to symmetrical deformation vibrations of CH3 in MB units) and 892 cm -1 (vibrations of the eyclohexano ring [2]). Since weak absorption of VCH units also occurs at 1385 cm-L the optical densities of the bands are expressed as MB VCH D13ss~[KlasSCMB-~Klas5 "(1--CMB)]l D 891 __ - - ~~/'VCH 892
(1--CMB)
* Vysokomol. soyed. AI8: ~o. 8, 1813-1818, 1976. 2075
g,
(1) (2)
2076
Y ~ . YA. GOL'DF&RB et a~.
where K are the absorption coefficients of the respective bands, / is the film width, and c - is the mole fraction of biB in the copolymer. T h e calibration curve for measurement of the copolymer compositions is expressed as VCH VCE[ MB V C H Dlsss/Dsss = Klsss /Km + (K18sdKm ) Ct,B/(1-- CMB) ,
/(MS/wVCH_ where ]FffVCH//(VCH--o'9"(from the P¥CH spectrum), and __lsss,_+m --_~-n v (calculated from the values of the absorption coefficients of the appropriate bands in the spectra of t h e homopolymers). The spectra of mixtures of the homopolymers were used to verify the calibration curve. A URS-50IK apparatus was used for recording X-ray diffraction patterns of the copolymers and homopolymers of MB and ~7CH (powders prepared in the course of copolymerization); the I)TA curves were plotted with the aid of the Paulik-Paulik-Erden derivatograph. Calcined Al~Os was Used as the standard. The rate of heating was 3 deg/min; each test sample weighed 0.150 g.
Structure of the M B - V C H co2aolymers. The copolymerization constants for MB and VCH (r 1 and rs respectively) based on the Fineman-Ross method [3] w e r e 1.02 and 0.98 respectively.. The fact t h a t the constants are close to u n i t y means t h a t the reactivities of the two monomers are practically identical, which, as was said above, is due to their structural similarity. Judging by the p r o d u c t of rlr 2, the copolymerization of MB with VCH would seem to take place with formation of copolymers t h a t are statistical in character. On going from homopolymers of MB and VCH to MB-VCH copolymers, one finds changes appearing in several of the physical characteristics of the latter. One normally finds t h a t bands in the I R spectra of olefin copolymers t h a t are most sensitive to the distribution of monomer units are those t h a t are sensitive to stereospecificity in the spectra of the homopolymers [1]. Among the bands most sensitive to stereospecificity in the PMB spectrum is t h a t at 778 cm -1 pertaining to the vibrations of large isotactic blocks. The addition of as little as ~ 10% o f VCH units into the eopolymer already leads to a ~ 2 fold reduction in the relative intensity of the band in question (the "isotacticity" index for MB units in t h e copolymer is 48% [4]), while the band at 778 cm -1 disappears entirely from t h e spectra of copolymers with > 2 0 % contents of VCH units. Behaviour of this t y p e on the part of stereospecificity bands in the spectra of the copolymers is characteristic of copolymers with structures t h a t are statistical in character. A comparison of the I R spectra of MB-VCH copolymers of varying composition revealed a further band t h a t is sensitive to the distribution of MB units, i,e. the band at 1118 cm -1. The optical density of the latter band is described by t h e expression MB
Dms---:KlllSCMB~cn+ll,
(3)
where ~.+1 is the fraction of MB units in the total number of blocks exceeding n units in length. Combining expressions (1)-(3) we obtain the following expression for the relative intensity of the 1118 cm-1 band normalized for the total number of biB units
Copolymers of 3-methylbutene.1 and vinyleyclohexane
2077
in t h e c o p o l y m e r
DM8
K~liis
(DI,,5--0"2Ds,=) : K~B5 = K . + ,
The value of =~nlS/==za85, UMB / u = s measured in the PM-B spectra, is 0.22. Figure 1 shows plots of [D1zts/(Dzass-O'2Dag=)/0.22 (A) a n d t h e calculated plots o f K#+l vs. c o p o l y m e r composition, s t a r t i n g w i t h values for rzrs= 1 given in [1]. On c o m p a r i n g t h e e x p e r i m e n t a l a n d theoretical d a t a it can be seen t h a t for t h e b a n d a t 1118 cm -1 n'-' 6-7.
A 1.0
b
oe /00
\\ ,
r,
i
60
----
~Z?
C M s , mole %
FIO. 1
I zo
I I0 FIG. 2
28"
FiG. 1. Relative intensity of the band at 1118 cm -1 in the IR spectra of the MB-YCH c o ° polymers vs. copolymer composition (see text): points--experimental data; the plots o f K6 and K7 are theoretical curves FIO. 2. Diffraction patterns of PMB (1), PVCH (5), and MB-VCH copolymers with VCH contents of 16 (2), 73 (3) and 95% (4). I t was d e m o n s t r a t e d in [2] t h a t t h e distribution of V C H units in V C H co. p o l y m e r s m a y be d e t e r m i n e d f r o m the i n t e n s i t y ratio o f c o m p o n e n t s of the doublet, a t 892-884 cm -1 characterizing v i b r a t i o n s of t h e cyclohexane ring. The i n t e n s i t y o f the 892 cm -1 b a n d in t h e P V C H s p e c t r u m exceeds t h a t of t h e b a n d at 884 c m -1, while t h e reverse is o b s e r v e d in the spectra o f t h e copolymers.
"2078
Y ~ . YA. (~OL'DFAI~B e~ a[.
A similar phenomenon is likewise found in the spectra of the MB-VCH co:polymers: in the PVCH spectrum D89~/Dss~~ 1.2, with an 84% MB content it is ~ 1-0, and ~0.6 for a 90~/o MB content. Figure 2 shows the diffraction patterns of PMB and PVCH powders and of t h e MB-VCH copolymers. The homopolymerization of MB results in a highly crystalline product. At the same time the homopolymerization of VCH results in a polymer that is only slightly crystalline in view of the higher glass transition of PVCH compared with the polymerization temperature [5]. I t can be seen from Fig. 2 that the addition of ~ 16% of VCH to the eopolymer is accompanied by practically complete amorphization of the product, which agrees with structure o f a statistical character envisaged for MB-VCH eopolymers. The broad reflection appearing in the region of 2 ~ 8-10 ° in the diffraction patterns of the copolymers is apparently attributable to reflections relating to planes parallel to the polymer chain axes (the corresponding reflection in the diffraction pattern of PMB is that with 2~--~10.4 ° corresponding to a reflection from the (100)* plane. As the VCH content in the eopolymers rises, the latter peak is displaced towards smaller angles (for PVCH 2 ~ 8.3 °) as a result of increased interehain spacings due to replacement of MB units by the more bulky VCH units. The DTA curves for PMB, PVCH and the MV-VCH eopolymers displayed in Fig. 3 were plotted while heating the samples in an argon atmosphere. The melting peak for PMB is situated at 300 °. The insertion of ~ 1 6 % of ¥ C H into the polymer brings the melting point down to ~275 °, and results in a m a r k e d diminution of the area under the melting peak, and in a widening of t h e peak, while in the case of the copolymer with a VCH content of ~50%, t h e melting peak is virtually absent. These changes are all in agreement with inferences that m a y be drawn from the Flory theory in regard to the melting of defective crystalline polymers and copolymers [7], according to which it appears that for copolymers with rl, r2-----1, the relation of the melting point to t h e content of a given component is described by the expression
1/T~ p - 1/T h°m°p• --(R/AH u) ln cM,
(4)
where R is the gas constant, AHu is the heat of melting for the homopolymer calculating for the monomer unit, and vM is the number of units of the given m o n o m e r in the copolymer. O n further increasing the VCH content in the eopolymer a weak peak begins t o appear on DTA curves for the melting of VCH crystalline blocks: with 73% VCH at ~290 °, 95°/o ~340 ° (for PVCH Tm----375-380 ° [5]). I t can be seen from Figs. 2 and 3 t h a t t h e crystallinity of VCH blocks in the copolymers, like the ~rystallinity of PVCH itself, is extremely low immediately after polymerization, s l t h o u g h as the number of VCtt blocks decreases reductions in the melting points e f t h e latter can be detected on the DTA curves, which is likewise consistent * Assignment of the reflection is based on the data in [6].
Copolymers of 3-methylbutene-l and vinylcyc]ohcxane
2079
with what m a y be deduced from Flory's theory for statistical copolymers. Using formula (4) the molar heats of melting determined for PlVI~ and PVOH from the melting point data amount to ~4400 and 3300 cal/mole. I n view of the total amount of data based on I R and X-ray analysis and DTA it can therefore be s~id that the MB-VCH copolymers have statistical structures. This is also borne out by the value of rlr =for the pair of monomers in question. LIT
!
I.
tO0
I
JO0
FIG. 3
I v
I
500 T,°C
36O
~ Fro. 4
0,0 T,~
~FiG. 3. DTA curves of PMB (1), PVCH (6), MB-VCH copolymers with VCH contents of 16 (2), 50 (3), 73 (4) and 95% (5). Fro. 4. Weight loss of polymers vs. temperature during heating in argon: 1-3, 5--MB-VCH copolymers (VCH content--16, 50, 73 and 95 mole ~/o respectively); 4--PMB; 6--PVCH. Thermal degradation of P M B and of M B - F C H co,polymers. With the aid of the derivatograms (DTG curves) the temperature intervals of decomposition during heating in argon were determined for PMB and M:B-VCH copolymers. The thermal degradation of PMB takes place over the range 360-450 ° (Fig. 3). Using the procedures outlined in Refs. [8, 9] we c~Iculated the average value of the activation energy E~ for the thermal degradation of PMB, and obtained Es----50 kcal/mole (360-400°). The thermal degradation of PVCH and poly-4methylpentene-1 (PMP) was investigated in papers [10, 11]; it was found t h a t PVCH and PMP decompose in the intervals 390-460 and 350-420 ° respectively; the respective values of E a are 56.5 and 54 kcal/mole. The thermal degradation data for the MB-VCH copolymers are displayed in Figs. 3 and 4. The MB-VCH copolymers with VCH units contents of 16, 50 and 73% (curves 1-3 in Fig. 4) have lower heat stability values than the homo-
2080
YU. YA. ~)L'DFARB 6~ ~ .
polymers (curves d, 6). The heat stability of the copolymer containing 95% VOH occupies an intermediate position between PMB and PVCH. It seems that there are two possible factors that could account for the lower heat stability of the copolymers compared with the homopolymers. The incorporation of foreign units, even quite stable one~ (VCH), into the homopolymer could lead to lower bond energy affecting units adjacent to VCH units, thereby facilitating degradation processes. Moreover, the insertion of foreign units will certainly cause disruption of short-range order in polymer melts, which will be another factor favouring degradation processes. /: G
z
•
I
200
II
2O0
¢00
600
I
2oo
~oo 7;, °c 8oo
FIG. 5. DTO (1), DTA (2) and TO (3) curves for PMB (a) and MB-~CCH (b) copolymers (50o//oVCH) during heating in air.
Thermooxidative degradation of MB-VCH copolymers. Derivatograms were recorded during the heating of PMB and MB-VCH copolymers in air. Figure 5 shows, as an example, the derivatograms of PMB and of the MB-VCH copolymer containing 50% VCH. In the light of the DTG and DTA curves one can identify the main stages in the decomposition of the PMB and the MB-VCtt copolymers: the first stage for PMB is at 170-260 °, the second at 260-380 ° and the third at 380-450°; the respective intervals for the copolymer are 200-260, 260-340 and 340-440 °. The first stage corresponds to thermooxidative degradation of the original polymeric hydrocarbons, and takes place via the formation and subsequent decomposition of hydroperoxides; it is accompanied by chain scission, and by the accumulation of oxygen-containing groups in the polymer. The gaseous degradation products released during this stage of the degradation of poIyolefins (water, aldehydes, ketones) contain relatively few 0 atoms, while carbonyl and carboxyl groups appear in the polymer, which means that there
Copolymers of 3-methylbuterm. 1 and viny|cyclohcxane
208I
is altogether no reduction in the weight of products (in the initial stages of oxidation it may even rise slightly (Fig. 5)). The reaction heat for PMB based on the area of the peak was found to be 350 cal/g. Since MB units and VCH units have each two vieinal tertiary H atoms, there is little relationship between the rates of processes of oxidative degradation of the copolymers and their compositions: with VCH contents in the range of 16-95 ~o there is practically no change in the temperature of the onset of oxidation (200--205°). In the second stage of decomposition rapid liberation of volatile products of high molecular weight takes place in the case of the PMB and the MB-VCH copolymer, and polyconjugated systems are formed. The third stage of thermooxidative degradation is characterized by reactions of rapid depletion of oxygencontaining carbonized products, and ends with practically complete conversion of the polymeric residue to gaseous products. Each monomer unit in the MP-VCH copolymers likewise contains two tertiary H atoms, and processes of thermooxidative degradation of these products are similarly practically independent of their composition: the onset of oxidation takes place at 190 ° [11]. The development of thermooxidative degradation of the studied products may be retarted through the introduction of antioxidants. Thus, whereas th~ onset of oxidation appears at 170 ° for unstabilized PMB, the introduction of 1%, of 2,6-ditert.butyl-4-ethyloleatophenol (Irganox 1076) raises the temperature to 210°; it is raised to 255 ° by phenyl-fl-naphthylamine, and to 265 ° by 2,2methylene-bis-4-methyl-6-tert.butylphenol (antioxidant 2246) or diphenyl-pphenylenediamine (the heating rate for the sample being 3 deg/min). Translated by R. J. A. HENDRY REFERENCES
1. Yu. V. KISSIN, Advances Polymer Sci. 15: 82, 1974 2. KHO UILEM, Yu. V. KISSIN, Yu. Ya. GOLDFARB and B. A. KRENTSEL, VysokomoL soyed. 14A: 2229, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 10, 2609, 1972) 3. M. FINEMAN and S. O. ROSS, J. Polymer Sci. 5: 269, 1950 4. Yu. V. KISSIN, Yu. Ira. GOLDFARB, Yu. V. NOVODERZHKIN and V. A. KRENTSEL,. Vysokomol. soycd. B18: 167, 1976 (Not t l a n s l a t e d in Polymer Sci. U.S.S.R.) 5. V. I. KLEINER, Dissertation, 1969 6. G. NATTA, P. CORRADINI and W. B . ~ S I , Rend. Accad. Nazl. Lincei, seric V I I I 19: 404, 1955 7. P. J. FLORY, Trans. F a r a d a y Soc. 51: 484, 1955 8. Z. REICH, Makromolek. Chem. 105: 233, 1967 9. G. O. PILOYAN, Vvedeniye v teoriyu termicheskogo analiza (Introduction to the theory of thermal analysis). Izd. "Mir", p. 148, 1968 10. V. I. KLEINER, N. A. NECHITAILO and L. L. STOTSKAYA, Plast. massy, 1~o. 11, 48, 1971 11. KHO UILEM, N. A. NECHITAILO, Yu. Ya. GOLDFARB, G. P. AFANASOVA and B. A . KRENTSEL, Plast. massy, No. 3, 57, 1972 \