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Chain transfer reactions and modification of the properties of polyorganosiloxanes
CHAIN TRANSFER REACTIONS AND MODIFICATION OF THE PROPERTIES OF POLYORGANOSILOXANES* K. A. ANDRIANOV, I. 1. TVERDOKKLEBOVA, S.-S. A. PAVLOVA, N. V. P~RTSOVA and N. L. ORLOVSKArA Institute of Hetero-organic Compounds, U.S.S.R. Academy of Sciences
(Received 11 June 1975)
I t is shown that in interchange reaction between polydimethylsiloxane (PDMS) with "blocked" end groups and "living" polymethylphenylsiloxane (PMPS), under the conditions chosen the preferential reaction is intra-, and not intermolecular exchange. In copolymerization of "living" PDMS and PMPS with polyisobutylphenylsilsesquioxane interehain exchange occurs, with formation of branched maeromolecules. The degree of reaction attained is about 20-30%.
THE reactive ends of "living" polyorganosfloxane molecules can under polymerization conditions take part in interchange reaction with polymer chain fragments at Si-O-Si linkages [1-10]. The properties of the final polymer wiU differ, depending on whether this interchange takes place intra- or intermolecularly. One of the methods for determining the nature of the processes involved is by monitoring the molecular weight parameters during the course of the interchange reaction. Since in intermolecular reaction the number of macromoleeules and their number average degree of polymerization do not alter during the course of an exchange reaction, the end product is a polymer with the equilibrium molecular weight distribution (MWD) corresponding to the minimal free energy of mixing of the fractions. A classical~ example of such a distribution is Flory's "most probable" distribution [11-15]. In the case of intrachain exchange either depolymerization simply occurs, i.e. formation of the original cyclic monomers, or formation of rings of different size [16-18]. In either case the final result will be formation of an equilibrium product. The aim of the present paper is to clarify the relative roles of inter- and intramolecular chain transfer in polyorganosiloxanes during an interchange reaction and to explore the possibility of making use of interchange reactions for modifying the properties of polyorganosiloxanes. * Vysokomol. soyed. A19: No. 1, 19-23, 1977, 20
Properties of polyorganosiloxanes
21
The following polyorganosfloxanes were used in interchange reactions: polydimethylsiloxane (PDMS), polymethylphenylsiloxane (PMPS) and polyisobutylphenylsilsesquioxane (PIBPS). The PDMS was prepared by polymerization of octamethylcyclotetrasiloxane by the method of reference [19], with (CI-I~)sSiON (CI:I3)~ as initiator, PMPS by polymerization of cis-trimethyltriphenylcyclotrisiloxane [20] and P I B P S by polymerization of a prepolymer of composition (C6ttlgSi~aO4.5)n, in the presence of K O t t for 3 hr at 235-240 ° [21]. The end groups were blocked by the method of reference [19]. Exchange interaction between PDMS and PMPS in the ratio of i : 1 was carried out in toluene at 80 ° for 3, 7, 12, 15 and 30 min. Interchange reaction of PDMS and PMPS with P I B P S was conducted at 80 °, 100 ° and 110 ° in 1~/o solution for 2, 4, 7, 10 and 50. The reactants in the ratios indicated in the Table, were placed in a flask provided with a stirrer, reflux condenser and capillary tube for delivering a current of argon. The reaction was monitored by withdrawing samples and measuring the intrinsic viscosity and molecular weight (MW). All the samples were brought to constant weight in a vacuum drying chamber at room temperature. The viscosity of the polymers was measured in a suspended-level, Ubbelohde viscometer, in toluene at 25 ° and in benzene at 20 °. The weight-average molecular weight 2~/~ was measured by the light-scattering method in a PPS-2 apparatus at an angle of 90 °, in methyl ethyl ketone and chloroform. Sedimentation curves were obtained by means of an MOM-120 ultracentrifuge at rotor of 50 rev/min, in toluene and benzene at concentrations of 0.5~ 0.75 and 1.0 g/100 ml.
o.8
d
/d T/me, m/,7
25
Fin. I. Variation in [e] during the course of heating a (1 : l) mixture of PDMS and PMPS at 80°: /--toluene, 25°; 2--benzene, 20%
I n r e a c t i o n b e t w e e n P D M S in w h i c h t h e e n d g r o u p s a r e " b l o c k e d " b y trimethylsilyl groups, and "living" macromolecules of PMPS both intermolecular a n d i n t r a m o l e c u l a r c h e m i c a l r e a c t i o n is possible. I n t e r c h a i n e x c h a n g e m u s t c a u s e i n c r e a s e in p o l y d i s p e r s i t y (Xw/Xn -~ 2), /tin r e m a i n i n g c o n s t a n t while 2tlw increases a n d c o n s e q u e n t l y [0] also increases. I n i n t r a c h a i n e x c h a n g e e l i m i n a t i o n o f low m o l e c u l a r e x c h a n g e p r o d u c t s (ring c o m p o u n d s ) b r i n g s a b o u t a fall in b o t h /~w a n d /14n, b u t /14n fails m o r e r a p i d l y t h a n /14w a n d in t h e l i m i t FCw/Xn-~ 2. I n t h e s e c i r c u m s t a n c e s [~] also d e c r e a s e s a n d t h e l o w m o l e c u l a r r i n g c o m p o u n d s plasticize t h e s y s t e m , c a u s i n g Tg t o fall t o l o w e r t e m p e r a t u r e s . As t h e s y s t e m is d i l u t e d t h e p r o b a b i l i t y o f i n t r a m o l e c u l a r c o n t a c t s i n c r e a s e s more than for intermolecular contacts and consequently the proportion of intram o l e c u l a r r e a c t i o n s increases, w i t h p r e f e r e n t i a l r i n g f o r m a t i o n . W e t h e r e f o r e chose
22
K . A . ANDRIANOV et ~ .
a concentration of the mixture of homopolymers slightly above the limiting concentration with respect to monomer for PDMS (the limiting concentration is the concentration below which polymerization of the monomer does not occur; for PDMS this is 4-10% by weight and for PMPS it is 0.5-5% by weight).
t
o
k:
I// I -too
-~o
0
-50
0
50
7",'C
FIG. 2. T h e r m o m e c h a n i e a l curves: a: 1 - - P D M S , 2 - - P M P S , 8 - - m i x t u r e of P D M S P M P S (1 : 1), 3 - 7 - - t h e s a m e m i x t u r e h e a t e d for 3, 7, 12, 15 a n d 30 rain a t 80°; b: / - - m i x t u r e of P D M S a n d P I B P S (0.23 : 0.77), 2 - - t h e s a m e after h e a t t r e a t m e n t for 50 h r a t 100 °.
Under the conditions chosen the reaction between PDMS and PIMPS is preferentially an intramolecular exchange reaction, [t/] falling from 0.7 to 0-3 (Fig. 1) and Mw from 116,500 to 86,000. There is little change in the numerical value of Tg (Fig. 2a) and the displacement of the thermo-mechanieal curves along the temperature scale can be exl~lained by formation of ring compounds of different size, which plasticize the system.
/ So
1./7
0.6
O.z !
8
g
So
7
Fxo. 8. S e d i m e n t a t i o n c o n s t a n t d i ~ r i b u t i o n curves: 1 - - P D M 8 , 2 ~ P M P S , 3 ~ - - r n i ~ m m o f P D M S and PMPS (1 : 1) h e a t e d for 15 a n d 40 m i n a t 80 °. i
and
Properties of polyorganosiloxanes
23
When a mixture of PDMS and PMPS homopolymers is heated for 30 min [~/] increases (Fig. 1) and the sedimentation constant distribution curve shifts toward higher values of the constant (Fig. 3). This could be a result of the occurrence of the intermolecular exchange reaction. However in the course of heating of this mixture the two maxima corresponding to the mixture do not disappear and a third maximum, corresponding to the products of the intermolecular exchange reaction does not appear. PARAMETERS OF INTERACTIONOF PDMS, PMPS AND PIBPS Initial -~/w X 10 -3 [n], dl/g weight Reaction ratio of temperature, original original mixture end product mixture ] end polysil°C polysiloxane PIBPS of poly- after 50 hr of poly- product oxanes mers mers 0"23:00877. 0.2 : 0-8 : 0.2 0.2:0.8
I:1 0.8:0.2
100 110 100 110 100 100
1"80 1"70 1"70
PDMS-PIBPS 4.00 3.50 4.00 3.60 1.43 1-69
3-10 2.80 0.82
1"07 1"07 1"02
PMPS-PIBPS 4.00 3.41 4.25 2.70 4.00 1.62
1.85 2-10 1.08
437
352
242
174
Thus when PDMS and PMPS are reacted together under the given conditions intramolecular exchange takes place preferentially, which would explain the high flexibility of the polysiloxane chains a n d the formation of rings of different size [1-4, 7-10].
! ,O
ZO
1I-
I
3g
18
5'Y
Time, hr
Fro. 4. D e p e n d e n c e of [q] on reaction time: 1--mixture of PMPS and PIBPS (1 : 1), 2--mixture of PMPS and PIBPS (0.2 : 0.8). F o r the purpose of modifying the properties of P I B P S interchange reactions between PDMS a n d PIBS, and between PMPS and PIBPS, were carried out. Since, as was shown above, in the early stages of exchange a t 80 ° intramolecular exchange predominates and intermolecular reaction does not occur, a longer
24
K. A. ANDRr~OV et al.
reaction time was chosen and in some instances the reaction temperature was raised to 100-110% Then the intermolecular exchange reaction should produce branched maeromoleeules, [~/] should fall and/hrw increase.
Fro. 5. Sedimentation diagram: /--mixture of PDMS and PIBPS (0.2 : 0.8); 2, 3--mixture heated for 3 and 50 hr respectively at 110°. When a mixture of PMPS and P I B P S is heated (Fig. 4, curves 1 and 2) it was found t h a t during the first hours of interchange reaction at 80-110 ° [r/] falls to a certain final value. When the curves of the dependence of [0] on the duration of interchange reaction between PMPS and P I B P S are composed (Fig. 4) it is seen that the time required to reach equilibrium is not dependent on the quantity of active end groups (i.e. on the relative amount of PMPS in the mixture), b u t the equilibr~m value of [0] is higher the higher the proportion of P I B P S in the mixture. Measurement of [0] and Alw of P M P S - P I B P S mixtures showed, for example, t h a t whereas a mixture consisting of 20% PMPS and 80% P I B P S had [~/]=3.4 and 3~w=242,000, after it has been heated for 50 hr [0]= 1.85 and lt~w= 174,000. A similar effect is found in interaction of PDMS and P I B P S (Table). Thus while the fall in [0] is considerable /14w decreases b y only about 20%, which is not much more than the experimental error in measurement b y the light scattering method (10-15%). F r o m this large decrease in viscosity and small decrease in ltiw it may be assumed that in addition to intramolecular exchange some intermolecular exchange, with formation of branched polymer, also occurs. When a mixture of PDMS and P I B P S (0.23 : 0.77) is heated at 100 ° for 50 hr Tg of the end product is about 60 ° above Tg of the original polymer mixture (Fig. 2b). In order to monitor the changes occurring during the course of exchange interaction, sedimentation diagrams of the homopolymers beforehand and during the course of reaction were plotted (Fig. 5). When the sedimentation diagrams are examined it is seen that the gradient curves of both the mixture of homopolymers and of the interchange product contain two peaks, b u t the area under them changes after heat treatment. Since the area bounded b y the gradient curve is a q u a n t i t y t h a t is proportional to the concentration of polymer and the refractive inde x increment of the polymer in the given solvent, the variation in this area
Properties of polyorganosiloxanes
25
w i t h r e a c t i o n t i m e can be used as a m e a s u r e of t h e degree o f r e a c t i o n of t h e polymers. W e calculated t h e c h a n g e in t h e w e i g h t ratio of t h e r e a c t a n t s in t h e reaction b e t w e e n P D M S a n d P I B P S , using t h e f o r m u l a w-~ m de ' where w is the w e i g h t f r a c t i o n o f t h e a p p r o p r i a t e h o m o p o l y m e r in t h e reaction mixture, m t h e a r e a u n d e r the g r a d i e n t c u r v e a n d dn/dc t h e refractive index increment. F o r a n unt r e a t e d m i x t u r e of P D M S a n d P I B P S a t a ratio b y w e i g h t of 0.23 : 0.77, calculation f r o m the s e d i m e n t a t i o n d i a g r a m g a v e a ratio close t o this. A f t e r t h e m i x t u r e h a d been h e a t e d for 50 h r t h e w e i g h t ratio of P D M S : P I B P S f o u n d f r o m the s e d i m e n t a t i o n d i a g r a m was 0 - 1 7 2 : 0 . 8 2 8 , i.e. the weight of P D M S h a d decreased a n d t h e weight fraction of t h e second r e a c t a n t h a d increased b y 6 0 . F r o m tlfis it m a y be a s s u m e d t h a t a t h i r d c o m p o n e n t of the s y s t e m has been f o r m e d , n a m e l y t h e p r o d u c t of i n t e r a c t i o n b e t w e e n the original two polymers.
Translated by E. O. PHILLIPS REFERENCES
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 1l. 12. 13. 14. 15. 16. 17. 18.
$. B. CARMICHAEL and J. HEFFEL, J. Phys. Chem. 69: 2218, 1965 J. B. CARMICHAEL and R. WINGER, J. Polymer Sci. A3: 971, 1965 J. B. CARMICKAEL and J. KINSIGER, Canadian J. Chem. 42: 1966, 1964 V. P. DAVYDOVA, N. A. PRAVIKOVA, T. A. YAKUSHINA and V. N. YAKOVLEVA, Vysokomol. soyed. 8: 436, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 3, 479, 1966) V. P. DAVYDOVA and Z. S. LEBEDEVA, Vysokomol soyed. B10: 401, 1968 (Not translated in Polymer Sci. U.S.S.R.) V. P. DAVYDOVA, Z. S. LEBEDEVA and I. A. GRYAZNYKH, Vysokomol soyed. Ag: 2226, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 10, 2518, 1967) F. P. ADAMS, J. B. CARMICHAEL and R. J. ZEMAN, J. Polymer Sci. A-I, 5: 741, 1967 S. W. KANTOR, W. T. GRUBB and R. S. OSTHOFF, J. Amer. Chem. Soe. 76: 249, 1954 F. P. ADAMS, J. B. CARMICHAEL and R. J. ZEMAN, Polymer Preprints 7: 960, 1966 J. B. CARMICHAEL and J. HEFFEL, J. Phys. Chem. 69: 7, 2213, 1965 A. A. BERLIN, V. V. IVANOV and N. S. YENIKOLOPYAN, Vysokomol. soyed. B9: 61, 1967 (Not translated in Polymer Sci. U.S.S.R.) V. V. IVANOV, N. A. SHAGINYAN and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSt{ 161: 1954, 1965 B. A. ROZENBERG, V. i. IRZHAK and N. S. YENIKOLOPYAN, Dok]. Akad. ~N'auk SSSR 170: 351, 1966 N. S. YENIKOLOPYAN, J. Polymer Sei. 58: 1301, 1962 A. MIJAKE and W. H. STOCKI~kYER, Makromolek. Chem. 88: 90, 1965 V. S. NANDA and S. C. JAIN, Kinetics and Mechanism of Polyreactions, Vol. 2, p. 69, Budapest, 1969 A. O. TONOYAN, S. P: DAVTYAN, B. A. ROZENBERG, V. I. IRZHAK and N. S. YENIKOLOPYAN, I)okl. Akad. ~Nauk SSSR 193: 862, 1970 B. A. I { O Z E N B E R G , N. V. M A K L E T S O V A , I. V. E N E L ' B A U M , Ye. B. LYUDVIG, and S. S. MEDVEDEV, Vysokomol. soyed. 7: 1051, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 6, 1163, 1965)
~26
T. F. ORESHENKOVA et a~o
19. N. V. PERTSOVA, K. A. ANDRIANOV, S. A. PAVLOVA and I. I. TVERDOI~HLEROVA, Vysokomol soyed. A12: 1001, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 5, 1131, 1970) 20. K. A. ANDRIANOV, S. A. PAVLOVA, I. I. TVERDOi~HT.EBOVA, N. V. PERTSOYA, V. S. SVISTUNOV and I. I. MAMAYEVA, Vysokomol. soyed. B15: 901, 1973 (Not translated in Polymer Sci. U.S.S.R.) 21. K. A. ANDRIANOV and N. N. MAKAROVA, Izv. Akad. Nauk SSSR, ser. khim., 625, 1969
PROTON MAGNETIC RESONANCE STUDY OF EQUILIBRIUM POLYMERIZATION OF TRIOXAN IN MODEL SYSTEMS* T. F. ORESHENKOVA, A. G. GRUZNOV, A. KH. BULAI,
I. YA. SLONI~ and L. M. ROMANOV Plastics Research Institute
(Received 27 _~rovember 1975) The redistribution with respect to molecular weight of the dlmethyl ethers of polyoxymethylene glycol (DE) in the presence of the cationic catalyst SnC14in benzene has been investigated. The equilibrium concentration of the cyclic monomers (trioxan and tetraoxan) and methylal, and the number average degree of polymerization of the dissolved polyoxymethylene (POM), were determined by the PMR method. The equilibrium constants of formation of dissolved and crystalline POM in polymerization of trioxan and tetraoxan in solution, and the equilibrium constant of transition of one --CH~O-- monomer unit from solution to a crystal lattice at different temperatures were calculated. The enthalphy and entropy changes involved in formation of liquid and crystalllne POM from the dissolved monomers, and the thermodynamic p a r a m ~ of crystallization of POM have been found.
CRYSTALLIZATIONOf & polymer during the course of polymerization affects the iclnetics and themodynaTnics of the process. Study of the effect of the solid phase on the kinetics of fermation of polyoxymethylene (POM) has been the subject of s number of papers [1, 2]. The present paper describes a study o f formation of crystalline and dissolved POM in model systems. The limiting concentrations of the monomers in relation to dissolved [4-7] and crystalline [3, 6] POM in v ~ i o u s solvents have been determined. The thermodynamic parameters of f ~ n of cry~alline and dissolved POM from monomers in different * Vysokomol. eoyed. AI~I,:No. 1, 24-31, 1977.
(Received 11 June 1975)
I t is shown that in interchange reaction between polydimethylsiloxane (PDMS) with "blocked" end groups and "living" polymethylphenylsiloxane (PMPS), under the conditions chosen the preferential reaction is intra-, and not intermolecular exchange. In copolymerization of "living" PDMS and PMPS with polyisobutylphenylsilsesquioxane interehain exchange occurs, with formation of branched maeromolecules. The degree of reaction attained is about 20-30%.
THE reactive ends of "living" polyorganosfloxane molecules can under polymerization conditions take part in interchange reaction with polymer chain fragments at Si-O-Si linkages [1-10]. The properties of the final polymer wiU differ, depending on whether this interchange takes place intra- or intermolecularly. One of the methods for determining the nature of the processes involved is by monitoring the molecular weight parameters during the course of the interchange reaction. Since in intermolecular reaction the number of macromoleeules and their number average degree of polymerization do not alter during the course of an exchange reaction, the end product is a polymer with the equilibrium molecular weight distribution (MWD) corresponding to the minimal free energy of mixing of the fractions. A classical~ example of such a distribution is Flory's "most probable" distribution [11-15]. In the case of intrachain exchange either depolymerization simply occurs, i.e. formation of the original cyclic monomers, or formation of rings of different size [16-18]. In either case the final result will be formation of an equilibrium product. The aim of the present paper is to clarify the relative roles of inter- and intramolecular chain transfer in polyorganosiloxanes during an interchange reaction and to explore the possibility of making use of interchange reactions for modifying the properties of polyorganosiloxanes. * Vysokomol. soyed. A19: No. 1, 19-23, 1977, 20
Properties of polyorganosiloxanes
21
The following polyorganosfloxanes were used in interchange reactions: polydimethylsiloxane (PDMS), polymethylphenylsiloxane (PMPS) and polyisobutylphenylsilsesquioxane (PIBPS). The PDMS was prepared by polymerization of octamethylcyclotetrasiloxane by the method of reference [19], with (CI-I~)sSiON (CI:I3)~ as initiator, PMPS by polymerization of cis-trimethyltriphenylcyclotrisiloxane [20] and P I B P S by polymerization of a prepolymer of composition (C6ttlgSi~aO4.5)n, in the presence of K O t t for 3 hr at 235-240 ° [21]. The end groups were blocked by the method of reference [19]. Exchange interaction between PDMS and PMPS in the ratio of i : 1 was carried out in toluene at 80 ° for 3, 7, 12, 15 and 30 min. Interchange reaction of PDMS and PMPS with P I B P S was conducted at 80 °, 100 ° and 110 ° in 1~/o solution for 2, 4, 7, 10 and 50. The reactants in the ratios indicated in the Table, were placed in a flask provided with a stirrer, reflux condenser and capillary tube for delivering a current of argon. The reaction was monitored by withdrawing samples and measuring the intrinsic viscosity and molecular weight (MW). All the samples were brought to constant weight in a vacuum drying chamber at room temperature. The viscosity of the polymers was measured in a suspended-level, Ubbelohde viscometer, in toluene at 25 ° and in benzene at 20 °. The weight-average molecular weight 2~/~ was measured by the light-scattering method in a PPS-2 apparatus at an angle of 90 °, in methyl ethyl ketone and chloroform. Sedimentation curves were obtained by means of an MOM-120 ultracentrifuge at rotor of 50 rev/min, in toluene and benzene at concentrations of 0.5~ 0.75 and 1.0 g/100 ml.
o.8
d
/d T/me, m/,7
25
Fin. I. Variation in [e] during the course of heating a (1 : l) mixture of PDMS and PMPS at 80°: /--toluene, 25°; 2--benzene, 20%
I n r e a c t i o n b e t w e e n P D M S in w h i c h t h e e n d g r o u p s a r e " b l o c k e d " b y trimethylsilyl groups, and "living" macromolecules of PMPS both intermolecular a n d i n t r a m o l e c u l a r c h e m i c a l r e a c t i o n is possible. I n t e r c h a i n e x c h a n g e m u s t c a u s e i n c r e a s e in p o l y d i s p e r s i t y (Xw/Xn -~ 2), /tin r e m a i n i n g c o n s t a n t while 2tlw increases a n d c o n s e q u e n t l y [0] also increases. I n i n t r a c h a i n e x c h a n g e e l i m i n a t i o n o f low m o l e c u l a r e x c h a n g e p r o d u c t s (ring c o m p o u n d s ) b r i n g s a b o u t a fall in b o t h /~w a n d /14n, b u t /14n fails m o r e r a p i d l y t h a n /14w a n d in t h e l i m i t FCw/Xn-~ 2. I n t h e s e c i r c u m s t a n c e s [~] also d e c r e a s e s a n d t h e l o w m o l e c u l a r r i n g c o m p o u n d s plasticize t h e s y s t e m , c a u s i n g Tg t o fall t o l o w e r t e m p e r a t u r e s . As t h e s y s t e m is d i l u t e d t h e p r o b a b i l i t y o f i n t r a m o l e c u l a r c o n t a c t s i n c r e a s e s more than for intermolecular contacts and consequently the proportion of intram o l e c u l a r r e a c t i o n s increases, w i t h p r e f e r e n t i a l r i n g f o r m a t i o n . W e t h e r e f o r e chose
22
K . A . ANDRIANOV et ~ .
a concentration of the mixture of homopolymers slightly above the limiting concentration with respect to monomer for PDMS (the limiting concentration is the concentration below which polymerization of the monomer does not occur; for PDMS this is 4-10% by weight and for PMPS it is 0.5-5% by weight).
t
o
k:
I// I -too
-~o
0
-50
0
50
7",'C
FIG. 2. T h e r m o m e c h a n i e a l curves: a: 1 - - P D M S , 2 - - P M P S , 8 - - m i x t u r e of P D M S P M P S (1 : 1), 3 - 7 - - t h e s a m e m i x t u r e h e a t e d for 3, 7, 12, 15 a n d 30 rain a t 80°; b: / - - m i x t u r e of P D M S a n d P I B P S (0.23 : 0.77), 2 - - t h e s a m e after h e a t t r e a t m e n t for 50 h r a t 100 °.
Under the conditions chosen the reaction between PDMS and PIMPS is preferentially an intramolecular exchange reaction, [t/] falling from 0.7 to 0-3 (Fig. 1) and Mw from 116,500 to 86,000. There is little change in the numerical value of Tg (Fig. 2a) and the displacement of the thermo-mechanieal curves along the temperature scale can be exl~lained by formation of ring compounds of different size, which plasticize the system.
/ So
1./7
0.6
O.z !
8
g
So
7
Fxo. 8. S e d i m e n t a t i o n c o n s t a n t d i ~ r i b u t i o n curves: 1 - - P D M 8 , 2 ~ P M P S , 3 ~ - - r n i ~ m m o f P D M S and PMPS (1 : 1) h e a t e d for 15 a n d 40 m i n a t 80 °. i
and
Properties of polyorganosiloxanes
23
When a mixture of PDMS and PMPS homopolymers is heated for 30 min [~/] increases (Fig. 1) and the sedimentation constant distribution curve shifts toward higher values of the constant (Fig. 3). This could be a result of the occurrence of the intermolecular exchange reaction. However in the course of heating of this mixture the two maxima corresponding to the mixture do not disappear and a third maximum, corresponding to the products of the intermolecular exchange reaction does not appear. PARAMETERS OF INTERACTIONOF PDMS, PMPS AND PIBPS Initial -~/w X 10 -3 [n], dl/g weight Reaction ratio of temperature, original original mixture end product mixture ] end polysil°C polysiloxane PIBPS of poly- after 50 hr of poly- product oxanes mers mers 0"23:00877. 0.2 : 0-8 : 0.2 0.2:0.8
I:1 0.8:0.2
100 110 100 110 100 100
1"80 1"70 1"70
PDMS-PIBPS 4.00 3.50 4.00 3.60 1.43 1-69
3-10 2.80 0.82
1"07 1"07 1"02
PMPS-PIBPS 4.00 3.41 4.25 2.70 4.00 1.62
1.85 2-10 1.08
437
352
242
174
Thus when PDMS and PMPS are reacted together under the given conditions intramolecular exchange takes place preferentially, which would explain the high flexibility of the polysiloxane chains a n d the formation of rings of different size [1-4, 7-10].
! ,O
ZO
1I-
I
3g
18
5'Y
Time, hr
Fro. 4. D e p e n d e n c e of [q] on reaction time: 1--mixture of PMPS and PIBPS (1 : 1), 2--mixture of PMPS and PIBPS (0.2 : 0.8). F o r the purpose of modifying the properties of P I B P S interchange reactions between PDMS a n d PIBS, and between PMPS and PIBPS, were carried out. Since, as was shown above, in the early stages of exchange a t 80 ° intramolecular exchange predominates and intermolecular reaction does not occur, a longer
24
K. A. ANDRr~OV et al.
reaction time was chosen and in some instances the reaction temperature was raised to 100-110% Then the intermolecular exchange reaction should produce branched maeromoleeules, [~/] should fall and/hrw increase.
Fro. 5. Sedimentation diagram: /--mixture of PDMS and PIBPS (0.2 : 0.8); 2, 3--mixture heated for 3 and 50 hr respectively at 110°. When a mixture of PMPS and P I B P S is heated (Fig. 4, curves 1 and 2) it was found t h a t during the first hours of interchange reaction at 80-110 ° [r/] falls to a certain final value. When the curves of the dependence of [0] on the duration of interchange reaction between PMPS and P I B P S are composed (Fig. 4) it is seen that the time required to reach equilibrium is not dependent on the quantity of active end groups (i.e. on the relative amount of PMPS in the mixture), b u t the equilibr~m value of [0] is higher the higher the proportion of P I B P S in the mixture. Measurement of [0] and Alw of P M P S - P I B P S mixtures showed, for example, t h a t whereas a mixture consisting of 20% PMPS and 80% P I B P S had [~/]=3.4 and 3~w=242,000, after it has been heated for 50 hr [0]= 1.85 and lt~w= 174,000. A similar effect is found in interaction of PDMS and P I B P S (Table). Thus while the fall in [0] is considerable /14w decreases b y only about 20%, which is not much more than the experimental error in measurement b y the light scattering method (10-15%). F r o m this large decrease in viscosity and small decrease in ltiw it may be assumed that in addition to intramolecular exchange some intermolecular exchange, with formation of branched polymer, also occurs. When a mixture of PDMS and P I B P S (0.23 : 0.77) is heated at 100 ° for 50 hr Tg of the end product is about 60 ° above Tg of the original polymer mixture (Fig. 2b). In order to monitor the changes occurring during the course of exchange interaction, sedimentation diagrams of the homopolymers beforehand and during the course of reaction were plotted (Fig. 5). When the sedimentation diagrams are examined it is seen that the gradient curves of both the mixture of homopolymers and of the interchange product contain two peaks, b u t the area under them changes after heat treatment. Since the area bounded b y the gradient curve is a q u a n t i t y t h a t is proportional to the concentration of polymer and the refractive inde x increment of the polymer in the given solvent, the variation in this area
Properties of polyorganosiloxanes
25
w i t h r e a c t i o n t i m e can be used as a m e a s u r e of t h e degree o f r e a c t i o n of t h e polymers. W e calculated t h e c h a n g e in t h e w e i g h t ratio of t h e r e a c t a n t s in t h e reaction b e t w e e n P D M S a n d P I B P S , using t h e f o r m u l a w-~ m de ' where w is the w e i g h t f r a c t i o n o f t h e a p p r o p r i a t e h o m o p o l y m e r in t h e reaction mixture, m t h e a r e a u n d e r the g r a d i e n t c u r v e a n d dn/dc t h e refractive index increment. F o r a n unt r e a t e d m i x t u r e of P D M S a n d P I B P S a t a ratio b y w e i g h t of 0.23 : 0.77, calculation f r o m the s e d i m e n t a t i o n d i a g r a m g a v e a ratio close t o this. A f t e r t h e m i x t u r e h a d been h e a t e d for 50 h r t h e w e i g h t ratio of P D M S : P I B P S f o u n d f r o m the s e d i m e n t a t i o n d i a g r a m was 0 - 1 7 2 : 0 . 8 2 8 , i.e. the weight of P D M S h a d decreased a n d t h e weight fraction of t h e second r e a c t a n t h a d increased b y 6 0 . F r o m tlfis it m a y be a s s u m e d t h a t a t h i r d c o m p o n e n t of the s y s t e m has been f o r m e d , n a m e l y t h e p r o d u c t of i n t e r a c t i o n b e t w e e n the original two polymers.
Translated by E. O. PHILLIPS REFERENCES
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$. B. CARMICHAEL and J. HEFFEL, J. Phys. Chem. 69: 2218, 1965 J. B. CARMICHAEL and R. WINGER, J. Polymer Sci. A3: 971, 1965 J. B. CARMICKAEL and J. KINSIGER, Canadian J. Chem. 42: 1966, 1964 V. P. DAVYDOVA, N. A. PRAVIKOVA, T. A. YAKUSHINA and V. N. YAKOVLEVA, Vysokomol. soyed. 8: 436, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 3, 479, 1966) V. P. DAVYDOVA and Z. S. LEBEDEVA, Vysokomol soyed. B10: 401, 1968 (Not translated in Polymer Sci. U.S.S.R.) V. P. DAVYDOVA, Z. S. LEBEDEVA and I. A. GRYAZNYKH, Vysokomol soyed. Ag: 2226, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 10, 2518, 1967) F. P. ADAMS, J. B. CARMICHAEL and R. J. ZEMAN, J. Polymer Sci. A-I, 5: 741, 1967 S. W. KANTOR, W. T. GRUBB and R. S. OSTHOFF, J. Amer. Chem. Soe. 76: 249, 1954 F. P. ADAMS, J. B. CARMICHAEL and R. J. ZEMAN, Polymer Preprints 7: 960, 1966 J. B. CARMICHAEL and J. HEFFEL, J. Phys. Chem. 69: 7, 2213, 1965 A. A. BERLIN, V. V. IVANOV and N. S. YENIKOLOPYAN, Vysokomol. soyed. B9: 61, 1967 (Not translated in Polymer Sci. U.S.S.R.) V. V. IVANOV, N. A. SHAGINYAN and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSt{ 161: 1954, 1965 B. A. ROZENBERG, V. i. IRZHAK and N. S. YENIKOLOPYAN, Dok]. Akad. ~N'auk SSSR 170: 351, 1966 N. S. YENIKOLOPYAN, J. Polymer Sei. 58: 1301, 1962 A. MIJAKE and W. H. STOCKI~kYER, Makromolek. Chem. 88: 90, 1965 V. S. NANDA and S. C. JAIN, Kinetics and Mechanism of Polyreactions, Vol. 2, p. 69, Budapest, 1969 A. O. TONOYAN, S. P: DAVTYAN, B. A. ROZENBERG, V. I. IRZHAK and N. S. YENIKOLOPYAN, I)okl. Akad. ~Nauk SSSR 193: 862, 1970 B. A. I { O Z E N B E R G , N. V. M A K L E T S O V A , I. V. E N E L ' B A U M , Ye. B. LYUDVIG, and S. S. MEDVEDEV, Vysokomol. soyed. 7: 1051, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 6, 1163, 1965)
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T. F. ORESHENKOVA et a~o
19. N. V. PERTSOVA, K. A. ANDRIANOV, S. A. PAVLOVA and I. I. TVERDOI~HLEROVA, Vysokomol soyed. A12: 1001, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 5, 1131, 1970) 20. K. A. ANDRIANOV, S. A. PAVLOVA, I. I. TVERDOi~HT.EBOVA, N. V. PERTSOYA, V. S. SVISTUNOV and I. I. MAMAYEVA, Vysokomol. soyed. B15: 901, 1973 (Not translated in Polymer Sci. U.S.S.R.) 21. K. A. ANDRIANOV and N. N. MAKAROVA, Izv. Akad. Nauk SSSR, ser. khim., 625, 1969
PROTON MAGNETIC RESONANCE STUDY OF EQUILIBRIUM POLYMERIZATION OF TRIOXAN IN MODEL SYSTEMS* T. F. ORESHENKOVA, A. G. GRUZNOV, A. KH. BULAI,
I. YA. SLONI~ and L. M. ROMANOV Plastics Research Institute
(Received 27 _~rovember 1975) The redistribution with respect to molecular weight of the dlmethyl ethers of polyoxymethylene glycol (DE) in the presence of the cationic catalyst SnC14in benzene has been investigated. The equilibrium concentration of the cyclic monomers (trioxan and tetraoxan) and methylal, and the number average degree of polymerization of the dissolved polyoxymethylene (POM), were determined by the PMR method. The equilibrium constants of formation of dissolved and crystalline POM in polymerization of trioxan and tetraoxan in solution, and the equilibrium constant of transition of one --CH~O-- monomer unit from solution to a crystal lattice at different temperatures were calculated. The enthalphy and entropy changes involved in formation of liquid and crystalllne POM from the dissolved monomers, and the thermodynamic p a r a m ~ of crystallization of POM have been found.
CRYSTALLIZATIONOf & polymer during the course of polymerization affects the iclnetics and themodynaTnics of the process. Study of the effect of the solid phase on the kinetics of fermation of polyoxymethylene (POM) has been the subject of s number of papers [1, 2]. The present paper describes a study o f formation of crystalline and dissolved POM in model systems. The limiting concentrations of the monomers in relation to dissolved [4-7] and crystalline [3, 6] POM in v ~ i o u s solvents have been determined. The thermodynamic parameters of f ~ n of cry~alline and dissolved POM from monomers in different * Vysokomol. eoyed. AI~I,:No. 1, 24-31, 1977.