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Some features of free-radical copolymerization of ethylene and vinyl acetate (under pressure) in the presence of acetaldehyde
2026
S . M . SAMOrLOVet a/.
32. R. A. ROBINSON and R. H. STOKES, Rastvory elektrolitov (Electrolyte Solutions). Foreign Literature Publishing House, 1963 (Russian translation) 33. V. P. BARABANOV, Dissertation, 1963 34. V. Ye. LOZHgIN, Dissertation, 1964 35. R. KERBER, Makromol. Chem. 96: 36, 1966
SOME FEATURES OF FREE-RADICAL COPOLYMERIZATION OF ETHYLENE AND VINYL ACETATE (UNDER PRESSURE) IN THE PRESENCE OF ACETALDEHYDE* S. M. SAMOILOV, ~V~.B. KOI~STANTII~'OPOL'SKAYA,_A_.p . GOLOSOV, Z. YA. ]~ERESTNEVA, V. ~ . KARGII~ a n d V. N. MONASTYRSKII L. Ya. Karpov Physicochemical Institute
(Received 22 May 1967) IT has been f o u n d r e c e n t l y t h a t aldehydes, especially a c e t a l d e h y d e (AA), can regulate the f r e e - r ~ i c a l polymerization o f some m o n o m e r s to produce stereoregular, highly crystalline polymers [1-4]. The stereoregulating effect o f aldehydes in copolymerization has however n o t y e t been studied. I t was o f interest to find t h e effect of AA on the kinetics o f radical copolymerization of e t h y l e n e (E) a n d vinyl a c e t a t e (VA), a n d also on t h e s t r u c t u r e a n d properties o f the copolymer. The ethylene used was of petroleum origin (purity 99"7~/o,containing 7, 1, 4 and 5 parts per milion of O~, CzH~, COs and CO respectively), the vinyl acetate had b.p. 72°, it contained
0.012~o of acetic acid and was free from hydroqninone, and the acetaldehyde was 99"9~o pure, containing 0.044o//o of crotonaldehyde and 0.03% of acetic acid, and was free from acetylene. Copolymerization was carried out in the laboratory apparatus described previously [5, 6]. The initiator was chemically pure tertiary butyl peroxide, which was added as a solution in the VA. No other solvents were used. The reaction mixture was analysed for AA by different methods, qualitatively by the Schiff reaction or chromatographically (didecyl phthalate followed by dloctyl sebacate on NaC1, 25°, carrier gas Ha, 30 cm*/min, flame ionization detector), and qualitatively, from 0.065 mole~/o upward, by the hydroxylamine method [7]. I t Was f o u n d t h a t w h e n E is copolymerized w i t h VA u n d e r high pressure AA is f o r m e d in the reaction zone. F o r example a f t e r a " b l a n k " e x p e r i m e n t in a n autoclave a t r o o m t e m p e r a t u r e u n d e r a pressure o f 1400 a t m a n d w i t h o u t a n initiator a n E - V A m i x t u r e gave no trace of colour w i t h Schiff's reagent. I f however a m i x t u r e of the same composition is copolymerized Schiff's r e a g e n t * Vysokomol. soyed. A10: No. 8, 1749-1754, 1968.
Free-radical copolymerization of ethylene and vinyl acetate
2027
becomes coloured w h e n o n l y one fiftieth o f t h e v o l u m e o f reaction p r o d u c t s is passed t h r o u g h it in c o m p a r i s o n w i t h t h e b l a n k e x p e r i m e n t (Table 1). I t is e v i d e n t t h a t t h e A A is f o r m e d b y chemical r e a c t i o n o f YA during t h e course o f copolymerization, because f o r m a t i o n of small a m o u n t s o f AA has been o b s e r v e d in radical h o m o p o l y m e r i z a t i o n o f VA a t 120 ° u n d e r m o d e r a t e pressure [8]. TABLE 1.
C O P O L Y M E R I Z A T I O N OF S
w~'~'~t V2~k Ilq" A-~ AUTOCLAVE IIq T H E PRESENCE OF L A R G E
CO~C~.~rrRATIO~S OF I~EGULATO~ (140 arm, 140°, 2 hr, initial VA concentration 5 mole%, tertiary butyl peroxide 0.01 mole%) Product
None Acetaldehyde Ditto ,, Chloroform Ditto ,,
1.5 5.0 7.5 0.4 5.0 7.5
19.5
83.53 14.04
-
2.3 82.46 13.941 1.6 79.16 13.26 I 1.4 80.42 13.35 i 14.9 82.52 13.98 0.60 7.9 80.00 13.35 5.27 6.7 75.15 12.65 6.80
2.6
-
3.0 1.6 6.1
0.2 1.5 2-0
1-292 105
90
0.0115
1.064 1.043 1.013 1.082 1.066 1.020
108 103 107
98 92 95
0.0106 0.0084 0-0103
101
94
0.0077
*0.035 g in 25 ml of decaUn at 100 °.
T h e r a t e o f f o r m a t i o n o f AA is v e r y low however, a n d therefore in one-pass e x p e r i m e n t s w i t h o u t gas recirculation, A A has n o t been d e t e c t e d in the reaction products. I n e x p e r i m e n t s in which the u n r e a c t e d p r o d u c t s are recircnlated AA g r a d u a l l y a c c u m u l a t e s a n d is easily d e t e c t e d b y c h r o m a t o g r a p h y a f t e r a few hours f r o m the c o m m e n c e m e n t o f the e x p e r i m e n t (Fig. 1). I n order t o find the effect on t h e process o f the AA f o r m e d during copolymerization o f E a n d VA, a series o f e x p e r i m e n t s (one-pass w i t h o u t recirculation) was c o n d u c t e d , in which AA was a d d e d to the initial charge, t h e composition of which was set w i t h great precision. T h e results are p r e s e n t e d in Table 2, a few analyses o v e r a n interval o f 1-2 h r being given for each e x p e r i m e n t . I t is seen t h a t AA acts as a typical chain t r a n s f e r agent. I t s c o n c e n t r a t i o n in the u n r e a c t e d p r o d u c t s was close to its c o n c e n t r a t i o n in t h e initial m i x t u r e . As t h e A A c o n c e n t r a t i o n was increased the molecular weight (M) o f the copolymers, m e a s u r e d b y intrinsic viscosity, fell a n d the melt index rose. L o w concentrations o f A A (within the limits studied) do n o t affect the kinetics of c o p o l y m e r i z a t i o n significantly. I t is seen from T a b l e 2 t h a t the yield o f co-
2028
S.M.
SAMOILOV et a~.
polymer is not affected. The conversion of E and VA, and consequently their reactivities, also remain practically unchanged. The VA content* of the copolymer and of the unreacted products was practically the same in all experiments.
/f b
a
c
Time
FIo. 1. Sections of chromatograms of reaction products from copolymerization of E with VA (one-pass apparatus at 220°, 1400 arm): a--with gas recirculation (acetaldehyde content 0.1 mole%, vinyl acetate content 2.8 mole%), b--one-pass, experiment 1, c--one-pass, experiment 4, with addition of 0.4°/o of acetaldehyde. For study of the effect of large concentrations of AA on the copolymerization of E and VA experiments were carried out in autoclaves (Table 1) at AA concentrations of 1.5-7.5 mole%. The AA was added in solution in the VA charge, the quantity of which, as well as the other experimental conditions, was kept strictly the same. Note that in these experiments the quantities of VA and AA quoted refer to the initial moment of reaction. During the reaction the system was diluted with pure E in order to maintain the pressure. The average quantities of VA and AA in the uureacted mixture were therefore lower than the original quantities. Table 1 shows that in high concentration AA lowers both M and the degree of conversion to polymer considerably. This is seen from the decrease in the relative viscosity of solutions of the eopolymers in decalin and from the decrease in the yield of polymer. The Tables show that as the concentration of AA is increased (up to 1.5 mole %) the melting point (Tin) and drystallization temperature (Tcr) of the copolymers, corresponding to the peaks in the differential thermographie curves, successively increase (reference material--liquidparaffin, a copper-eonstantan thermocouple of diameter 0.1 mm immersed directly in the sample; the rate of heating and cooling was 2 deg/min, with a precision of 0.5-1.0 ° [9]; the reproducibility of the results was thoroughly tested). Table 2 shows that as well as T~ the density of the copolymers (measured in a pyknometer) also increases in the presence of AA at low concentrations. Both * The VA content of the copolymer was found from the carbon content, and of the gaseous mixture by the method of reference [7].
Free-radlcal copolymerizationof ethylene and vinyl acetate
2029
these effects indicate increase in the degree of ordering of the crystalline structure. An increase in crystallinity can also be seen directly from the increase in the area under the crystallization peak in the DTA curves in experiments with small quantities of AA. In order to discover the mechanism of the action of AA copolymers 1-4 were studied in greater detail. Figure 2 shows the results of fractionation of copolymers 1 and 3 by fractional elution. It is seen that in the main the AA terminates chains that have already attained a certain length and as a result of this the quantity of high molecular weight polymer is reduced and the proportion of fractions of molecular weight in the middle range is increased. The proportion of copolymer of low molecular weight is practically unchanged. The composition of all the fractions of both copolymers (by elementary analysis) was close to the average composition of the copolymer, though as M increases the VA content decrease~ to some extent. The infrared spectra of films confirmed the higher degree of crystallinity of copolymers prepared in the presence of AA. The ratio of the degrees of crysta|linity (730 cm -1 band [10]) of copolymers 4 and 1 was 1-18, which is in good agreement with the ratio of the areas under the DTA peaks of these copolymers, which was 1.16. The number and intensity of all the other spectral bands of all fractions of copelymers 1-4 were the same and no difference in the structure of the molecules was disclosed. The low-resolution N1VIR spectra of copolymers 1 and 3 in the temperature range of --78 ° to -~20 ° also failed to disclose any structural difference. All this indicates that low concentrations of AA do not affect the relative reactivities of E and VA in radical copolymerization under pressure. The increase in crystallinity, density, T m and T~ of copolymers under the influence of AA is due to decrease in the proportion of molecules with a high degree of polymerization, as a result of chain termination. We have shown previously that low molecular weight fractions of PE (low density) crystallize in the form of more perfect supermolecular structures (plate-like crystals) in comparison with high molecular weight fractions (spherulites). As a result of this the crystallinity, Tin, Tcr and density fall as the molecular weight of PE fractions increases. The same relationship holds for E-VA eopelymers [11]. Electron-microscopic study showed that although both copolymers have a fibrillar structure the nature and size of the fibrils are quite different. The fibrils in copolymer 4, which was prepared in the presence of AA (Fig. 3b) are mostly considerably larger and less well defined than those in copolymers prepared in the absence of AA. This pattern was found both in the high molecular weight copolymer 1 (Fig. 3a) and in a low molecular weight E-VA copolymer prepared in the absence of AA under conditions similar to those used for copolymers 1-4 (Fig. 3c). Thus the presence of AA during copolymerization leads primarily to reduction in the proportion of high molecular weight fractions. In addition it is evident
2. E F F E C T OF LOW CONCENTRATIONS OF RECI~RCUI~TION
A_~ ON COPOLYMERIZATION OF E AND V A n~ A o~r~-PASS APPAraTUS WrrnOUT GAS
2.7 2.5 -2.7 3.3 -2.7 3.2 3.0 2.9 2.8 2.3
0 0 0 0.084 0.084 0.084 0.27 0.27 0.27 0.51 0.51 0-51 0-41 0.41 0"63
0.31 0.24
0 0 0 0.096 0"084
AA in mixt u r e , m o l e ~o
* Weight of corresponding p a r t of diagram.
20-21 21-22 22-23 19-20 20-21 21-22 18-19 20-21 21-22 15-16 17-18 18-19
.~
240 210 200 27O 260 310 240 260 260 265 160 470
83.18 88.31 83-60 83.06 82.90 83.62 83.54 83-34 83.20 83.50 83.85 83.70
13.82 14-04 13.76 13"81 13.84 13"95 13.66 13"97 13.72 13.95 13"75 13.94
2.9 2.8 2.4 3.1 3.3 2.4 2.5 2.7 2-9 2-5 2.0 2"3 0.37
0-77
1"16
1.34
0-927 0.923 0.919 0"934 0.938 0"931 0.929 0"938 0.935 0"935 0-935 0.935
100 82 !0-0200 72.6 100 83 72.0 99 83 69"9 70.1 69.2 1001 86 i0.0216 67-5 75.4 70"9 10~ 87 0"0225 78"8 77"7 77.1 103 88 0.0232 91.1
Product
96.3 96"5 99.4 81"0 79.4 70.6 62"6 60"6 66"1 66.9 70.0 82.4
560 550 630 510 530 450 160 220 190 110 90 120
1-5 0"8 1"4 10"2 15-3 7"9 75 89 91 430 438 446
(1400 a r m , 220 °, t i m e i n r e a c t i o n z o n e ~ 30 sec, c o n c e n t r a t i o n o f V A i n initial m i x t u r e 2"8 mole°/o, t e r t . b u t y l p e r o x i d e 0.0002 mole~o)
TABLE
"~
o
t~ f~
Free-radical copolymerization of ethylene and vinyl acetate
2031
that in E-VA copolymers prepared in the presence of AA the mobility of the elementary structural elements (fibrils) is greater than in copolymers prepared without AA. This results in increase in the size of the supermolecular structure but the general nature of the copolymer is unaffected. The increase in the size of
~ fooI
0.5
,
,
f'O
1"5
['1 ], dz/9 Fza. 2. Fractional composition of E-VA copolymers: 1--experiment I (without acetaldehyde);
2--experiment 3 (with addition of 0.27 mole % of acetaldehyde to the reaction mixture).
the structures in the eopolymer inevitably affects its themomechanical characteristics. I t is seen from Table 2 that under the influence of AA the breaking strength a n d elongation at break decrease, but the yield point is raised, i.e. as the size of the fibrils increase the copolymers become more rigid and brittle. On the other hand low molecular weight E-VA copolymers prepared in the absence of AA
FIG. 3. Supermolecular structure of E-VA copolymer containing 2.7 mole % of VA: a--high molecular weight ([v/]=1.34), prepared in the absence of acetaldehyde (experiment 1); b--low molecular weight ([t/I-----0"37),prepared in the presence of acetaldehyde (experiment 4); c--low molecular weight ([t/]=0.39), prepared in the absence of acetaldehyde.
in which there is no such large increase in the size of the fibrils, do not have a raised yield point and they can still undergo considerable stretching. It is evident that the changes described above in the structure of the copolymer should occur when chain transfer agents causing a reduction in M, other
2032
S . M . SAMOW.OVeta/.
than AA, are added. Experiments in the autoclave in the presence of chloroform (CF) (Table 1) in fact showed that in addition to a decrease in M CF caused T m and Tcr to increase. With very large increase in the regulator concentration T m and T= pass through a maximum. Thus T m and Tc~ fall when the AA or CF content is greater than the VA content by a factor of 1.5. Here, however, one must take into account the fact that at such high concentrations the regulator enters the composition of the copolymer in significant amounts. In fact if the composition of such a copolymer is calculated (this calculation can be made from the elementary composition only for copolymers containing CF) it is found that the CF content of the copolymer is comparable with the VA content. It is obvious that the same complication of the copolymer composition occurs when AA is used in large concentratious. Consequently when the regulator concentration is high the chemical composition of the copolymers is altered to such an extent that direct comparison of their properties with those of copolymers prepared in the presence of small proportions of regulator is not possible. Moreover with very high concentrations of regulator oligomers, not polymers, are obtained. It should be noted that the vinyl chloride polymers discussed in references [3] and [4] in all probability contained significant amounts of aldehydes because a specific effect was observed only when equimolar proportions or an excess of aldehyde was added to the system. However, in these papers the effect of aldehyde units on the properties of polyvinylchloride was completely ignored. Thus AA is a typical chain transfer agent. Its presence in the copolymerizing system leads to reduction in the molecular weight of the product. This in turn causes increase in the crystallinity, density, T m and T = of E - ¥ A copolymers. Moreover, as comparison of electronrnicrographs shows, copolymers with the same M, obtained in the presence of absence of AA, have some structural differences. E V A copolymers prepared in the presence of AA contain larger fibrillar structures, which are evidently more densely packed, and this causes a change in properties, namely a decrease in breaking strength and elongation at brcak, while at the same time the yield point is raised. Thus E V A copolymers prepared in the presence of AA have poorer mechanical qualities. CONCLUSIONS
(1) Very small quantities of acetaldehyde (AA) are formed during radical copolymerization of ethylene (E) and vinyl acetate (VA) under pressure. Concentrations of AA up to 0.5 mole ~ do not affect the yield of the copolymer but at higher concentrations the yield is reduced. (2) The reduction in the molecular weight (M) of the copolymer when AA in quantities >0.08 mole ~/o is added to the reaction mixtures indicates t h a t AA is a typical chain transfer agent. As a result of the decrcase in M the density, crystallinity, T m and T~r of the copolymer increase.
Molecular relaxation in poly.p-cyemoethylmethacrylate
2033
(3) C o p o l y m e r s w i t h t h e s a m e v a l u e o f M p r e p a r e d in t h e presence a n d a b s e n c e o f AA, a n d h a v i n g t h e s a m e m o r p h o l o g i c a l t y p e o f s t r u c t u r e , differ in t h e size o f t h e fibrillar s t r u c t u r e s a n d e v i d e n t l y also in t h e i r p a c k i n g density. T h i s results in d e t e r i o r a t i o n o f t h e m e c h a n i c a l characteristics o f c o p o l y m e r s p r e p a r e d in t h e presence o f AA. Translated by E. O. Pm'LY.J.PS REFERENCES 1. P. H. BURLEIGH, J. Amer. Chem. Soc. 82: 749, 1960 2. J. ROSEN, P. H. BURLEIGH and J. F. GH.LESPIE, J. Polymer Sci. 54: 31, 1961 3. G. A. RAZUVAYEV, K. S. MINSKER, A. G. KRONMAN, Yu. A. SANGALOV and D. N. BORT, ]:)ok]. Akad. Nauk SSSR 148: 1116, 1962 4. G. A. RAZUVAYEV, K. S. MINS]gER, A. G. KRONMAN and Yu. A. SANGALOV, Vysokomol. soyed. 5: 1615, 1963 (Translated in Polymer Sci. U.S.S.R. 5: 5, 721, 1964) 5. S. M. SAMOILOV, A. P. GOLOSOV, A. N. ZEL'DIN and V. N. MONASTYRSKH, Plast. massy, No. 5, 3, 1966 6. R. A. TERENTYAN, A. N. ZEL'DIN, S. M. SAMOILOV, M. Kh. ATAKAZOVA and V. N. MONASTYRSIgH~ Vysokomol soyed. 8: 1721, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 10, 1898, 1966) 7. S. M. SAMOILOV, V. N. MONASTYRSKH and L. N. YUDKINA, Plast. massy, No. 11, 62, 1966 8. H. KORBANKA, Chem. Techn. 9: 67, 1957 9. B. A. FRENKEL', S. M. SAMOILOV and L. Ye. ~ O V , Neftezavodskoye i neftelehlmlcheskoye obordovanie, No. 3, 1, 1967 10. M. C. TOBIN and M. CARRANO, J. Polymer Sci. 24: 93, 1957 11. S. M. 8AMOILOV, M. B. KONSTANTINOPOL'SKAYA, Z. Ya. BERESTNEVA and V.A. KARGIN, Vysokomol. soyed. A9: 1316, 1967 (Translated in Polymer Sci. U.S.S.R. 9A: 6, 1473, 1967)
MOLECULAR
RELAXATION
IN POLY-p-CYANOETHYL-
METHACRYLATE
*
G. P. M r ~ A n . O V (dec.), A. I. ARTYtn~OV a n d T. I. BORISOVA Institute of Macromolecular Compounds, U.S.S.R Academy of Sciences
(Received 28 August 1967) POLYMERS containing side chains w i t h e n d g r o u p s o f high m o b i l i t y d i s p l a y r e l a x a t i o n processes a t low t e m p e r a t u r e s in electrical a n d m e c h a n i c a l fields o f acoustic f r e q u e n c y . T h e y a r e d i s p l a y e d in t e m p e r a t u r e (or f r e q u e n c y ) relationships in t h e f o r m o f m a x i m a in t h e dielectric loss f a c t o r (~") a n d t h e i m a g i n a r y * Vysokomol. soyed. A1@: No. 8, 1755-1761, 1968.
S . M . SAMOrLOVet a/.
32. R. A. ROBINSON and R. H. STOKES, Rastvory elektrolitov (Electrolyte Solutions). Foreign Literature Publishing House, 1963 (Russian translation) 33. V. P. BARABANOV, Dissertation, 1963 34. V. Ye. LOZHgIN, Dissertation, 1964 35. R. KERBER, Makromol. Chem. 96: 36, 1966
SOME FEATURES OF FREE-RADICAL COPOLYMERIZATION OF ETHYLENE AND VINYL ACETATE (UNDER PRESSURE) IN THE PRESENCE OF ACETALDEHYDE* S. M. SAMOILOV, ~V~.B. KOI~STANTII~'OPOL'SKAYA,_A_.p . GOLOSOV, Z. YA. ]~ERESTNEVA, V. ~ . KARGII~ a n d V. N. MONASTYRSKII L. Ya. Karpov Physicochemical Institute
(Received 22 May 1967) IT has been f o u n d r e c e n t l y t h a t aldehydes, especially a c e t a l d e h y d e (AA), can regulate the f r e e - r ~ i c a l polymerization o f some m o n o m e r s to produce stereoregular, highly crystalline polymers [1-4]. The stereoregulating effect o f aldehydes in copolymerization has however n o t y e t been studied. I t was o f interest to find t h e effect of AA on the kinetics o f radical copolymerization of e t h y l e n e (E) a n d vinyl a c e t a t e (VA), a n d also on t h e s t r u c t u r e a n d properties o f the copolymer. The ethylene used was of petroleum origin (purity 99"7~/o,containing 7, 1, 4 and 5 parts per milion of O~, CzH~, COs and CO respectively), the vinyl acetate had b.p. 72°, it contained
0.012~o of acetic acid and was free from hydroqninone, and the acetaldehyde was 99"9~o pure, containing 0.044o//o of crotonaldehyde and 0.03% of acetic acid, and was free from acetylene. Copolymerization was carried out in the laboratory apparatus described previously [5, 6]. The initiator was chemically pure tertiary butyl peroxide, which was added as a solution in the VA. No other solvents were used. The reaction mixture was analysed for AA by different methods, qualitatively by the Schiff reaction or chromatographically (didecyl phthalate followed by dloctyl sebacate on NaC1, 25°, carrier gas Ha, 30 cm*/min, flame ionization detector), and qualitatively, from 0.065 mole~/o upward, by the hydroxylamine method [7]. I t Was f o u n d t h a t w h e n E is copolymerized w i t h VA u n d e r high pressure AA is f o r m e d in the reaction zone. F o r example a f t e r a " b l a n k " e x p e r i m e n t in a n autoclave a t r o o m t e m p e r a t u r e u n d e r a pressure o f 1400 a t m a n d w i t h o u t a n initiator a n E - V A m i x t u r e gave no trace of colour w i t h Schiff's reagent. I f however a m i x t u r e of the same composition is copolymerized Schiff's r e a g e n t * Vysokomol. soyed. A10: No. 8, 1749-1754, 1968.
Free-radical copolymerization of ethylene and vinyl acetate
2027
becomes coloured w h e n o n l y one fiftieth o f t h e v o l u m e o f reaction p r o d u c t s is passed t h r o u g h it in c o m p a r i s o n w i t h t h e b l a n k e x p e r i m e n t (Table 1). I t is e v i d e n t t h a t t h e A A is f o r m e d b y chemical r e a c t i o n o f YA during t h e course o f copolymerization, because f o r m a t i o n of small a m o u n t s o f AA has been o b s e r v e d in radical h o m o p o l y m e r i z a t i o n o f VA a t 120 ° u n d e r m o d e r a t e pressure [8]. TABLE 1.
C O P O L Y M E R I Z A T I O N OF S
w~'~'~t V2~k Ilq" A-~ AUTOCLAVE IIq T H E PRESENCE OF L A R G E
CO~C~.~rrRATIO~S OF I~EGULATO~ (140 arm, 140°, 2 hr, initial VA concentration 5 mole%, tertiary butyl peroxide 0.01 mole%) Product
None Acetaldehyde Ditto ,, Chloroform Ditto ,,
1.5 5.0 7.5 0.4 5.0 7.5
19.5
83.53 14.04
-
2.3 82.46 13.941 1.6 79.16 13.26 I 1.4 80.42 13.35 i 14.9 82.52 13.98 0.60 7.9 80.00 13.35 5.27 6.7 75.15 12.65 6.80
2.6
-
3.0 1.6 6.1
0.2 1.5 2-0
1-292 105
90
0.0115
1.064 1.043 1.013 1.082 1.066 1.020
108 103 107
98 92 95
0.0106 0.0084 0-0103
101
94
0.0077
*0.035 g in 25 ml of decaUn at 100 °.
T h e r a t e o f f o r m a t i o n o f AA is v e r y low however, a n d therefore in one-pass e x p e r i m e n t s w i t h o u t gas recirculation, A A has n o t been d e t e c t e d in the reaction products. I n e x p e r i m e n t s in which the u n r e a c t e d p r o d u c t s are recircnlated AA g r a d u a l l y a c c u m u l a t e s a n d is easily d e t e c t e d b y c h r o m a t o g r a p h y a f t e r a few hours f r o m the c o m m e n c e m e n t o f the e x p e r i m e n t (Fig. 1). I n order t o find the effect on t h e process o f the AA f o r m e d during copolymerization o f E a n d VA, a series o f e x p e r i m e n t s (one-pass w i t h o u t recirculation) was c o n d u c t e d , in which AA was a d d e d to the initial charge, t h e composition of which was set w i t h great precision. T h e results are p r e s e n t e d in Table 2, a few analyses o v e r a n interval o f 1-2 h r being given for each e x p e r i m e n t . I t is seen t h a t AA acts as a typical chain t r a n s f e r agent. I t s c o n c e n t r a t i o n in the u n r e a c t e d p r o d u c t s was close to its c o n c e n t r a t i o n in t h e initial m i x t u r e . As t h e A A c o n c e n t r a t i o n was increased the molecular weight (M) o f the copolymers, m e a s u r e d b y intrinsic viscosity, fell a n d the melt index rose. L o w concentrations o f A A (within the limits studied) do n o t affect the kinetics of c o p o l y m e r i z a t i o n significantly. I t is seen from T a b l e 2 t h a t the yield o f co-
2028
S.M.
SAMOILOV et a~.
polymer is not affected. The conversion of E and VA, and consequently their reactivities, also remain practically unchanged. The VA content* of the copolymer and of the unreacted products was practically the same in all experiments.
/f b
a
c
Time
FIo. 1. Sections of chromatograms of reaction products from copolymerization of E with VA (one-pass apparatus at 220°, 1400 arm): a--with gas recirculation (acetaldehyde content 0.1 mole%, vinyl acetate content 2.8 mole%), b--one-pass, experiment 1, c--one-pass, experiment 4, with addition of 0.4°/o of acetaldehyde. For study of the effect of large concentrations of AA on the copolymerization of E and VA experiments were carried out in autoclaves (Table 1) at AA concentrations of 1.5-7.5 mole%. The AA was added in solution in the VA charge, the quantity of which, as well as the other experimental conditions, was kept strictly the same. Note that in these experiments the quantities of VA and AA quoted refer to the initial moment of reaction. During the reaction the system was diluted with pure E in order to maintain the pressure. The average quantities of VA and AA in the uureacted mixture were therefore lower than the original quantities. Table 1 shows that in high concentration AA lowers both M and the degree of conversion to polymer considerably. This is seen from the decrease in the relative viscosity of solutions of the eopolymers in decalin and from the decrease in the yield of polymer. The Tables show that as the concentration of AA is increased (up to 1.5 mole %) the melting point (Tin) and drystallization temperature (Tcr) of the copolymers, corresponding to the peaks in the differential thermographie curves, successively increase (reference material--liquidparaffin, a copper-eonstantan thermocouple of diameter 0.1 mm immersed directly in the sample; the rate of heating and cooling was 2 deg/min, with a precision of 0.5-1.0 ° [9]; the reproducibility of the results was thoroughly tested). Table 2 shows that as well as T~ the density of the copolymers (measured in a pyknometer) also increases in the presence of AA at low concentrations. Both * The VA content of the copolymer was found from the carbon content, and of the gaseous mixture by the method of reference [7].
Free-radlcal copolymerizationof ethylene and vinyl acetate
2029
these effects indicate increase in the degree of ordering of the crystalline structure. An increase in crystallinity can also be seen directly from the increase in the area under the crystallization peak in the DTA curves in experiments with small quantities of AA. In order to discover the mechanism of the action of AA copolymers 1-4 were studied in greater detail. Figure 2 shows the results of fractionation of copolymers 1 and 3 by fractional elution. It is seen that in the main the AA terminates chains that have already attained a certain length and as a result of this the quantity of high molecular weight polymer is reduced and the proportion of fractions of molecular weight in the middle range is increased. The proportion of copolymer of low molecular weight is practically unchanged. The composition of all the fractions of both copolymers (by elementary analysis) was close to the average composition of the copolymer, though as M increases the VA content decrease~ to some extent. The infrared spectra of films confirmed the higher degree of crystallinity of copolymers prepared in the presence of AA. The ratio of the degrees of crysta|linity (730 cm -1 band [10]) of copolymers 4 and 1 was 1-18, which is in good agreement with the ratio of the areas under the DTA peaks of these copolymers, which was 1.16. The number and intensity of all the other spectral bands of all fractions of copelymers 1-4 were the same and no difference in the structure of the molecules was disclosed. The low-resolution N1VIR spectra of copolymers 1 and 3 in the temperature range of --78 ° to -~20 ° also failed to disclose any structural difference. All this indicates that low concentrations of AA do not affect the relative reactivities of E and VA in radical copolymerization under pressure. The increase in crystallinity, density, T m and T~ of copolymers under the influence of AA is due to decrease in the proportion of molecules with a high degree of polymerization, as a result of chain termination. We have shown previously that low molecular weight fractions of PE (low density) crystallize in the form of more perfect supermolecular structures (plate-like crystals) in comparison with high molecular weight fractions (spherulites). As a result of this the crystallinity, Tin, Tcr and density fall as the molecular weight of PE fractions increases. The same relationship holds for E-VA eopelymers [11]. Electron-microscopic study showed that although both copolymers have a fibrillar structure the nature and size of the fibrils are quite different. The fibrils in copolymer 4, which was prepared in the presence of AA (Fig. 3b) are mostly considerably larger and less well defined than those in copolymers prepared in the absence of AA. This pattern was found both in the high molecular weight copolymer 1 (Fig. 3a) and in a low molecular weight E-VA copolymer prepared in the absence of AA under conditions similar to those used for copolymers 1-4 (Fig. 3c). Thus the presence of AA during copolymerization leads primarily to reduction in the proportion of high molecular weight fractions. In addition it is evident
2. E F F E C T OF LOW CONCENTRATIONS OF RECI~RCUI~TION
A_~ ON COPOLYMERIZATION OF E AND V A n~ A o~r~-PASS APPAraTUS WrrnOUT GAS
2.7 2.5 -2.7 3.3 -2.7 3.2 3.0 2.9 2.8 2.3
0 0 0 0.084 0.084 0.084 0.27 0.27 0.27 0.51 0.51 0-51 0-41 0.41 0"63
0.31 0.24
0 0 0 0.096 0"084
AA in mixt u r e , m o l e ~o
* Weight of corresponding p a r t of diagram.
20-21 21-22 22-23 19-20 20-21 21-22 18-19 20-21 21-22 15-16 17-18 18-19
.~
240 210 200 27O 260 310 240 260 260 265 160 470
83.18 88.31 83-60 83.06 82.90 83.62 83.54 83-34 83.20 83.50 83.85 83.70
13.82 14-04 13.76 13"81 13.84 13"95 13.66 13"97 13.72 13.95 13"75 13.94
2.9 2.8 2.4 3.1 3.3 2.4 2.5 2.7 2-9 2-5 2.0 2"3 0.37
0-77
1"16
1.34
0-927 0.923 0.919 0"934 0.938 0"931 0.929 0"938 0.935 0"935 0-935 0.935
100 82 !0-0200 72.6 100 83 72.0 99 83 69"9 70.1 69.2 1001 86 i0.0216 67-5 75.4 70"9 10~ 87 0"0225 78"8 77"7 77.1 103 88 0.0232 91.1
Product
96.3 96"5 99.4 81"0 79.4 70.6 62"6 60"6 66"1 66.9 70.0 82.4
560 550 630 510 530 450 160 220 190 110 90 120
1-5 0"8 1"4 10"2 15-3 7"9 75 89 91 430 438 446
(1400 a r m , 220 °, t i m e i n r e a c t i o n z o n e ~ 30 sec, c o n c e n t r a t i o n o f V A i n initial m i x t u r e 2"8 mole°/o, t e r t . b u t y l p e r o x i d e 0.0002 mole~o)
TABLE
"~
o
t~ f~
Free-radical copolymerization of ethylene and vinyl acetate
2031
that in E-VA copolymers prepared in the presence of AA the mobility of the elementary structural elements (fibrils) is greater than in copolymers prepared without AA. This results in increase in the size of the supermolecular structure but the general nature of the copolymer is unaffected. The increase in the size of
~ fooI
0.5
,
,
f'O
1"5
['1 ], dz/9 Fza. 2. Fractional composition of E-VA copolymers: 1--experiment I (without acetaldehyde);
2--experiment 3 (with addition of 0.27 mole % of acetaldehyde to the reaction mixture).
the structures in the eopolymer inevitably affects its themomechanical characteristics. I t is seen from Table 2 that under the influence of AA the breaking strength a n d elongation at break decrease, but the yield point is raised, i.e. as the size of the fibrils increase the copolymers become more rigid and brittle. On the other hand low molecular weight E-VA copolymers prepared in the absence of AA
FIG. 3. Supermolecular structure of E-VA copolymer containing 2.7 mole % of VA: a--high molecular weight ([v/]=1.34), prepared in the absence of acetaldehyde (experiment 1); b--low molecular weight ([t/I-----0"37),prepared in the presence of acetaldehyde (experiment 4); c--low molecular weight ([t/]=0.39), prepared in the absence of acetaldehyde.
in which there is no such large increase in the size of the fibrils, do not have a raised yield point and they can still undergo considerable stretching. It is evident that the changes described above in the structure of the copolymer should occur when chain transfer agents causing a reduction in M, other
2032
S . M . SAMOW.OVeta/.
than AA, are added. Experiments in the autoclave in the presence of chloroform (CF) (Table 1) in fact showed that in addition to a decrease in M CF caused T m and Tcr to increase. With very large increase in the regulator concentration T m and T= pass through a maximum. Thus T m and Tc~ fall when the AA or CF content is greater than the VA content by a factor of 1.5. Here, however, one must take into account the fact that at such high concentrations the regulator enters the composition of the copolymer in significant amounts. In fact if the composition of such a copolymer is calculated (this calculation can be made from the elementary composition only for copolymers containing CF) it is found that the CF content of the copolymer is comparable with the VA content. It is obvious that the same complication of the copolymer composition occurs when AA is used in large concentratious. Consequently when the regulator concentration is high the chemical composition of the copolymers is altered to such an extent that direct comparison of their properties with those of copolymers prepared in the presence of small proportions of regulator is not possible. Moreover with very high concentrations of regulator oligomers, not polymers, are obtained. It should be noted that the vinyl chloride polymers discussed in references [3] and [4] in all probability contained significant amounts of aldehydes because a specific effect was observed only when equimolar proportions or an excess of aldehyde was added to the system. However, in these papers the effect of aldehyde units on the properties of polyvinylchloride was completely ignored. Thus AA is a typical chain transfer agent. Its presence in the copolymerizing system leads to reduction in the molecular weight of the product. This in turn causes increase in the crystallinity, density, T m and T = of E - ¥ A copolymers. Moreover, as comparison of electronrnicrographs shows, copolymers with the same M, obtained in the presence of absence of AA, have some structural differences. E V A copolymers prepared in the presence of AA contain larger fibrillar structures, which are evidently more densely packed, and this causes a change in properties, namely a decrease in breaking strength and elongation at brcak, while at the same time the yield point is raised. Thus E V A copolymers prepared in the presence of AA have poorer mechanical qualities. CONCLUSIONS
(1) Very small quantities of acetaldehyde (AA) are formed during radical copolymerization of ethylene (E) and vinyl acetate (VA) under pressure. Concentrations of AA up to 0.5 mole ~ do not affect the yield of the copolymer but at higher concentrations the yield is reduced. (2) The reduction in the molecular weight (M) of the copolymer when AA in quantities >0.08 mole ~/o is added to the reaction mixtures indicates t h a t AA is a typical chain transfer agent. As a result of the decrcase in M the density, crystallinity, T m and T~r of the copolymer increase.
Molecular relaxation in poly.p-cyemoethylmethacrylate
2033
(3) C o p o l y m e r s w i t h t h e s a m e v a l u e o f M p r e p a r e d in t h e presence a n d a b s e n c e o f AA, a n d h a v i n g t h e s a m e m o r p h o l o g i c a l t y p e o f s t r u c t u r e , differ in t h e size o f t h e fibrillar s t r u c t u r e s a n d e v i d e n t l y also in t h e i r p a c k i n g density. T h i s results in d e t e r i o r a t i o n o f t h e m e c h a n i c a l characteristics o f c o p o l y m e r s p r e p a r e d in t h e presence o f AA. Translated by E. O. Pm'LY.J.PS REFERENCES 1. P. H. BURLEIGH, J. Amer. Chem. Soc. 82: 749, 1960 2. J. ROSEN, P. H. BURLEIGH and J. F. GH.LESPIE, J. Polymer Sci. 54: 31, 1961 3. G. A. RAZUVAYEV, K. S. MINSKER, A. G. KRONMAN, Yu. A. SANGALOV and D. N. BORT, ]:)ok]. Akad. Nauk SSSR 148: 1116, 1962 4. G. A. RAZUVAYEV, K. S. MINS]gER, A. G. KRONMAN and Yu. A. SANGALOV, Vysokomol. soyed. 5: 1615, 1963 (Translated in Polymer Sci. U.S.S.R. 5: 5, 721, 1964) 5. S. M. SAMOILOV, A. P. GOLOSOV, A. N. ZEL'DIN and V. N. MONASTYRSKH, Plast. massy, No. 5, 3, 1966 6. R. A. TERENTYAN, A. N. ZEL'DIN, S. M. SAMOILOV, M. Kh. ATAKAZOVA and V. N. MONASTYRSIgH~ Vysokomol soyed. 8: 1721, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 10, 1898, 1966) 7. S. M. SAMOILOV, V. N. MONASTYRSKH and L. N. YUDKINA, Plast. massy, No. 11, 62, 1966 8. H. KORBANKA, Chem. Techn. 9: 67, 1957 9. B. A. FRENKEL', S. M. SAMOILOV and L. Ye. ~ O V , Neftezavodskoye i neftelehlmlcheskoye obordovanie, No. 3, 1, 1967 10. M. C. TOBIN and M. CARRANO, J. Polymer Sci. 24: 93, 1957 11. S. M. 8AMOILOV, M. B. KONSTANTINOPOL'SKAYA, Z. Ya. BERESTNEVA and V.A. KARGIN, Vysokomol. soyed. A9: 1316, 1967 (Translated in Polymer Sci. U.S.S.R. 9A: 6, 1473, 1967)
MOLECULAR
RELAXATION
IN POLY-p-CYANOETHYL-
METHACRYLATE
*
G. P. M r ~ A n . O V (dec.), A. I. ARTYtn~OV a n d T. I. BORISOVA Institute of Macromolecular Compounds, U.S.S.R Academy of Sciences
(Received 28 August 1967) POLYMERS containing side chains w i t h e n d g r o u p s o f high m o b i l i t y d i s p l a y r e l a x a t i o n processes a t low t e m p e r a t u r e s in electrical a n d m e c h a n i c a l fields o f acoustic f r e q u e n c y . T h e y a r e d i s p l a y e d in t e m p e r a t u r e (or f r e q u e n c y ) relationships in t h e f o r m o f m a x i m a in t h e dielectric loss f a c t o r (~") a n d t h e i m a g i n a r y * Vysokomol. soyed. A1@: No. 8, 1755-1761, 1968.