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Copolymerization of tetrahydrofuran with propylene oxide in the presence of methacrylic anhydride
2074
L. N. TUROVSKAYA et ~ .
9. D. P. WYMAN and I. H. SONG, Makromolok. Chem. 115: 64, 1968 10. V. P. SHATALOV, V. S. GLUKItOVSKOI, Yu. A. LITVIN, E. S. KOSTIN, A. R. SAMOTSVETOV and L. V. KOVTUNENKO, Zh. obsheh, khimii 41: 1921, 1971 11. M. BAER, J. Polymer Sei. 2A: 429, 1964 12. D. K. POLYAKOV, Dissertation, 1969 13. R. V. BASOVA and A. R. GANTMAKHF_,R, Vysokomol. soyed. 4: 361, 1962 (Translated in Polymer Sci. U.S.S.R. 4: 1, 118, 1963)
COPOLYMERIZATION OF TETRAHYDROFURAN WITH PROPYLENE OXIDE IN THE PRESENCE OF METHACRYLIC ANHYDRIDE * L. N. TUROVSKAYA, •. G. MATV~,Y~,VA and A. A. BERLIN Chemical Physics Institute,U.S.S.R. Academy of Sciences (Received 22 November 1971) A study is made of the effect of reaction conditions and of the ratio of the compon e n t s on the yield and molecular weight of copolymers obtained b y copolymerizing tetrahydrofuran with propylene oxide in the presence of methacrylic anhydride, using a n t i m o n y pentachloride as catalyst. The molecular weight of the oligomers, determined b y chemical and p h y s i c a l methods, is inversely proportional both to the a m o u n t of chain transfer agent and to catalyst concentration. The ratio of the molecular weight of oligomers, based on the bromine number, to the molecular weight found by measuring the heats of condensation, is reduced with increase in the molar ratio of methacrylic anhydride to SbC16, a n d reaches limiting values characteristic of the a m o u n t of SbC15. The limiting values of the molecular weight ratios are reduced with increase in the a m o u n t of SbCl 5, a n d are close to unity. The difference in the molecular weights determined by the physical and the chemical methods is due to the formation of nonfunctional products during the copolymerization process.
IN THE preparation of oligomers b y cationic polymerization and copolymerization of oxygen-containing rings in the presence of various chain transfer agents the feasibility of wide variations in both the size and structure of the oligomer block, as well as in the nature of the endgroups, has been demonstrated b y a number of investigators [1-9]. In earlier papers it was shown that in the homopolymerization of tetrahydrofuran (TtIF) in the presence of methacrylic anhydride (MA) variations in the MA concentration may be used as a means of regulating the molecular weight * Vysokomol. soyed. A15: No. 8, 1842-1846, 1973.
Copolymerization of tetrahydrofuran with propylene oxide
2075
of the resulting oligomers, a n d to o b t a i n a,~o-dimethacrylic derivatives o f oligot e t r a m e t h y l e n e glycols of the desired molecular weight [4, 5]. I n this connection our aim was to investigate the possibility of single-stage p r e p a r a t i o n of d i m e t h a c r y l i c esters of T H F - p r o p y l e n e oxide (PO) c o p o l y m e r s b y cationic c o p o l y m e r i z a t i o n of t h e m o n o m e r s in the presence of MA, u s i n g a n t i m o n y p e n t a c h l o r i d e as catalyst. EXPERIMENTAL
THF was freshly distilled in a column in an argon current over sodium bonzophenono, b.p. 66° n~° 1.4710 [10]. PO was freshly distilled on a column over calcium hydride in an argon current, b.p. 33.8 °, n~° 1.3664 [11]. MA was synthesized by the method described in reference [12], the fraction with b.p. 84% 11 ram, n~° 1.4530 was collected. SbC15 ("pure" grade) was used without further purification. The copolymerization was carried out in a four-necked vessel provided with a stirrer and thermometer. Before introducing the components the vessel was evacuated and filled with argon; the reactants were placed in the vessel in an argon current. The molar ratio of THF to PO was 3.33 in all the experiments. The catalyst was added, while stirring, to a mixture of the reactants that had been cooled to -- 30°, and the temperature was then raised to 0 ° over a 15-rain period. Stirring was stopped after rapid heat liberation had ceased, and the polymerizate was kept at 0 ° for 48 hr. By introducing the catalyst at --30 ~ it was possible to control the copolymerization temperature and avoid overheating, thereby ensuring the reporoducibility of the results. The separation of the product was effected by using the procedure outlined in [4]. The molecular weights of the oligomers were determined by measuring the heats of condensation ( ~ ) [13] and by hromination of terminal unsaturated groups (11~). To determine the amount of allyl and isopropenyl groups in the products of T H F - P O copolymerization, the possible formation of which was reported in [14], the monomers were copolymerized in the presence of acetic anhydride used as the chain transfer agent. The concentration of the latter was 0.1492 and 0.912 mole/1. Determination of the unsaturation of the resultant diacetates did not show the presence of double bonds in the products. The synthesized oligomers were liquids of different viscosities depending on the molecular weight, and were soluble in many organic solvents; during the polymerization they became insoluble network polymers. DISCUSSION OF RESULTS
A s t u d y was m a d e of the e x t e n t to which the conditions of T H F - P O c o p o l y m e r i z a t i o n in the presence of M_A, with SbC15 as catalyst, influenced the yield a n d molecular w e i g h t o f the products. As the time of the c o p o l y m e r i z a t i o n process was increased the o l i g o m e r yield rose, reaching a c o n s t a n t value (~55°/o) in 10 hr (Fig. 1). The r e l a t i v e l y low yields m a y be due to partial d e c a y of the active centres owing t o true t e r m i n a t i o n o f the growing chain. This is s u p p o r t e d b y the presence of chlorine in t h e products. The curves of ~tln a n d J l ~ / / l ~ vs. reaction time h a v e a m a x i m u m in a r o u n d 2 - 4 h r (Fig. 1). ~ , a n d / ~ of the oligomers are n o t equal, the value o f ~ generally being considerably higher t h a n Jl4~, which is a t t r i b u t a b l e to s u b s t a n c e s with e n d g r o u p s c o n t a i n i n g n o double b o n d s being p r e s e n t in the reaction p r o d u c t s .
2076
L.N.
TUROVSKAYA e$ a/.
•fO-3
J
8g
o-.--
2"5i
6" 40 2 a~-- i/¢
0"5
2I Z~
I
~e 7"~me,hr
72
FiG. 1. Plots of the yield (1), molecular weights ~ ' (2), and il~ of the oligomers (3) and the .,V4~'/~l~, ratio (4) vs. reaction time at 0°; T H F : PO ----3.33; SBC16----0.34;[MA] ~0.576 mole. Here and in Figs. 2-4 T H F = 0 . 1 9 7 2 , PO~0.0592 mole.
An inadequate number of functional groups as well as an extremal type of relationship found on plotting/11~ against reaction time was noted in [15-20] by authors investigating the polymerization and copolymerization of some heterocyclic monomers. a Ili7~,
a-
IZ ~
5 •
3 j
J
2 x..]
I
0
a
•
I
8 5 2
7
i
J
O.f
i
I
i 1.2
i
0
0.~
0"8
/'2[HAling/gill
FIG. 2. Plots of 1 / / ~ (a) and l / ~ ' ( b ) vs MA concentration; SbC15× 103~1"25 (1), 2.5 (2), 5 (3), 7.81 (d) and 10 moles (5). Here and in Figs. 3 and 4 the reaction time is 48 hr; 0 °.
Copolymerization of tetrahydrofuran with propylene oxide
2077
The Mn-values of the oligomers are inversely proportional both to MA concentration (Fig. 2) and to catalyst concentration (Fig. 3). The linearity of the 1/Mn vs. SbC15 plot is likewise preserved in the case of zero MA concentration. The values of 1 / ~ for [MA]----0 were obtained, by extrapolation, from Fig. 2.
b
lO
a
o
i 0.2
I 0"4
[SbC 5],
0
V -
[ 0"2
I
0"4, [SbC'~],mo/e//.
FIG. 3. Plots of 1 / ~ (a) and 1 / ~ ' (b) vs. catalyst concentration; MA × 103=33.5 (•); 19.95 (2) 13.26 (3); 2-76 (4) and 0 mole (5). The ~ / / l ~ ratio is reduced as the [MA]/[SbC15] ratio increased but a limiting molecular wt. ratio appears at particular values of the concentrations which are dependent on SbCl~ concentration. The limiting values of M~/114~ reduce with increasing catalyst concentration, and approach unity when the latter is high (Fig. 4). According to present-day ideas with regard to the mechanism of cationic polymerization of cyclic ethers in the presence of chain transfer agents [21, 22] MA taken in excess relative to catalyst will participate both in initiation, and in chain transfer, and will determine the nature of the endgroups. However, it is known that in cationic polymerization and copolymerization PO is capable of forming active centres without the participation of the cocatalyst [23-25]. I n this case chain termination reactions, namely cyclization involving catalyst
2078
L. N. TuRovs~YA et a/.
reactivation [26] and termination on gegen-ions by addition of anion residues (e.g. chloride) at the end of the molecule will lead to the formation of nonfunctional or chlorine-containing products.
I o
I B
,~l 16
t zO
FIG. 4. Change in the ~ ' / ~ ' ratio vs. molar ratio ofMA : SbCls; SbCI~= 103= 10 (•); 7.81 (2), 5 (3); 2-5 (4) and 1.25 mole (5). In the case of T H F - P O copolymerization the amount of nonfunctional compounds is apparently determined largely by the ratio of active centres formed at the stage of initiation both with and without the participation of MA, as well as by the occurrence of chain termination reactions, as a result of which nonfunctional oligomers are formed, in other words, other conditions being identical, the amount of nonfunctional compounds will depend on the P O : M A ratio. When the catalyst is added to the mixture of monomers and chain transfer agent at the start of the reaction, the PO concentration greatly exceeds the MA concentration, which favours the formation of active centres without the participation of MA. On increasing the amount of the latter, the probability of MA participating in the formation of active centres is increased, and this, along with chain transfer to anhydride and chain transfer accompanied by termination will in tote increase the amount of products with terminal methacrylate groups. Translated by R. J. A. H~ND~Y
REFERENCES
1. A. M. EASTMAN, Fortsch. Hochpol. Forsch. 2: 18, 1960 2. L. A. DICKISON, J. Polymer Sci. 58: 857, 1962 3. A. A. BERLIN, N. G. MATVEYEVA, E. S. MA_MEnOVA, E. S. PAPKOVA and L. M.
VOLK0VA, U.S.S.R. Pat. No. 191798, 1966; ByulL izob., No. 4, 1967 4. A. A. BERLIN, N. G. MATVEYEVA and E. S. PANKOVA, Vysokomol. soyed. A9: 1325, 1967 (Translated in Polymer Sei. U.S.S.R. 9: 6, 1485, 1967)
Copolymorization of tetrahydrofuran with propylene oxide
2079
5. A. A. BERLIN, N. G. MATVEYEVA, E. S. PANKOVA, O. G. SEL'SKAYA and G. I. KOREL'SKAYA, Vysokomol. soyed. A I 0 : 995, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 5, 1153, 1968) 6. V. A. KROPACHEV, A. B. ALFFAtOVA, B. A. DOLGOPLOSK, G. N. KUREN'GINA, • Yu. A. GORIN, K. N. CHARSKAYA and E. I. RODINA, U.S.S.R. Pat. No. 172042, 1964; Byull izob., No. 22, 94, 1966 7. M. I. REITBURD, G. S. BRODSKII, N. M. SHER and B. Ye. KONOVALOVA, Plast. massy, No. 3, 8, 1966 8. M. I. REITBURD, M. A. MARKEVICH and M. S. AKUTIN, Vysokomo]. soyed. A9: 1144, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 5, ]275, 1967) 9. O. G. TARAKANOV, Dissertation, 1967 ]0. T. SAEGUSA, H. IMAI and J. F U R U K A W A , Makromolek. Chem. 65: 60, 1963 1 ]. M. S. M~LISOVSKH, Okisi olefinov i ikh proizvodnye (O]efin Oxides and Derivatives). Izd. Goskhimizdat, 1961 ]2. U.S. Pat. 2143924; Chem. Zb]. 11: 73], 1939 13. Ye. Yu. BEKHLI, D. D. NOVIKOV and S. G. ENTELIS, Vysokomo]. soyed. A9: 2754, ]967 (Translated in Polymer Sci. U.S.S.R. 9: ]2, 3117, 1967) 14. D. D. NOVIKOV, Dissertation, 1971 15. L. P. BLANCKARD, J. SIGH and M. D. BAIJAL, Canad. J. Chem. 44: 2679, 1966 ]6. M. D. B A I J A L and L. P. BLANCHARD, J. Polymer Sci. C23: 157, 1968 ] 7. P. A. OKUNEV, A. G. OKUNEVA, O. G. TARAKANOV and I. A. VAKHTINA, Vysokomo]. soyed. A l l : 359, 1969 (Translated in P o l y m e r Sci. U.S.S.R. 11: 2, 403, 1969) 18. R. O. COLCLOUGH, G. H. GEE, W. C. E. HIGGINSON, J. B. JACKSON and M. ZITT, J. Polymer Sei. 34: ]71, 1959 19. R. J. K A T N I K and J. SHEAFER, J. ()rgan. Chem. 33: 384, 1968 20. H. KERN, J. Organ. Chem. 33: 387, ]968 21. Ye. B. LYUDVIG, B. A. ROZENBERG, T. M. ZVEREVA, A. R. GANTMAKHER and S. S. MEDVEDEV, Vysokomo]. soyed. 7: 269, 1965 (Translated in Polymer Sci. U.S.S.I~. 7: 2, 296, 1965) 22. T. SAEGUSA, H. JMAI and J. F U R U K A W A , Makromolek. Chem. 54: 60, 1962 23. H. MEERWEIN, D. DELFS and H. MORSHEL, Angew. Chemic 72: 927, 1960 24. B. A. ROZENBERG, Ye. B. LYUDVIG, N. V. DEMETOVA, A. It. GANTMAKHER and S. S. MEDVEDEV, Vysokomo]. soyed. 7: 1010, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 6, I l l 6 , 1965) 25. Ye. A. 0FSTEAD, Polymer Preprints 6: 613, 1965 26. E. L. ESTRIN, Thesis, 1968
\
L. N. TUROVSKAYA et ~ .
9. D. P. WYMAN and I. H. SONG, Makromolok. Chem. 115: 64, 1968 10. V. P. SHATALOV, V. S. GLUKItOVSKOI, Yu. A. LITVIN, E. S. KOSTIN, A. R. SAMOTSVETOV and L. V. KOVTUNENKO, Zh. obsheh, khimii 41: 1921, 1971 11. M. BAER, J. Polymer Sei. 2A: 429, 1964 12. D. K. POLYAKOV, Dissertation, 1969 13. R. V. BASOVA and A. R. GANTMAKHF_,R, Vysokomol. soyed. 4: 361, 1962 (Translated in Polymer Sci. U.S.S.R. 4: 1, 118, 1963)
COPOLYMERIZATION OF TETRAHYDROFURAN WITH PROPYLENE OXIDE IN THE PRESENCE OF METHACRYLIC ANHYDRIDE * L. N. TUROVSKAYA, •. G. MATV~,Y~,VA and A. A. BERLIN Chemical Physics Institute,U.S.S.R. Academy of Sciences (Received 22 November 1971) A study is made of the effect of reaction conditions and of the ratio of the compon e n t s on the yield and molecular weight of copolymers obtained b y copolymerizing tetrahydrofuran with propylene oxide in the presence of methacrylic anhydride, using a n t i m o n y pentachloride as catalyst. The molecular weight of the oligomers, determined b y chemical and p h y s i c a l methods, is inversely proportional both to the a m o u n t of chain transfer agent and to catalyst concentration. The ratio of the molecular weight of oligomers, based on the bromine number, to the molecular weight found by measuring the heats of condensation, is reduced with increase in the molar ratio of methacrylic anhydride to SbC16, a n d reaches limiting values characteristic of the a m o u n t of SbC15. The limiting values of the molecular weight ratios are reduced with increase in the a m o u n t of SbCl 5, a n d are close to unity. The difference in the molecular weights determined by the physical and the chemical methods is due to the formation of nonfunctional products during the copolymerization process.
IN THE preparation of oligomers b y cationic polymerization and copolymerization of oxygen-containing rings in the presence of various chain transfer agents the feasibility of wide variations in both the size and structure of the oligomer block, as well as in the nature of the endgroups, has been demonstrated b y a number of investigators [1-9]. In earlier papers it was shown that in the homopolymerization of tetrahydrofuran (TtIF) in the presence of methacrylic anhydride (MA) variations in the MA concentration may be used as a means of regulating the molecular weight * Vysokomol. soyed. A15: No. 8, 1842-1846, 1973.
Copolymerization of tetrahydrofuran with propylene oxide
2075
of the resulting oligomers, a n d to o b t a i n a,~o-dimethacrylic derivatives o f oligot e t r a m e t h y l e n e glycols of the desired molecular weight [4, 5]. I n this connection our aim was to investigate the possibility of single-stage p r e p a r a t i o n of d i m e t h a c r y l i c esters of T H F - p r o p y l e n e oxide (PO) c o p o l y m e r s b y cationic c o p o l y m e r i z a t i o n of t h e m o n o m e r s in the presence of MA, u s i n g a n t i m o n y p e n t a c h l o r i d e as catalyst. EXPERIMENTAL
THF was freshly distilled in a column in an argon current over sodium bonzophenono, b.p. 66° n~° 1.4710 [10]. PO was freshly distilled on a column over calcium hydride in an argon current, b.p. 33.8 °, n~° 1.3664 [11]. MA was synthesized by the method described in reference [12], the fraction with b.p. 84% 11 ram, n~° 1.4530 was collected. SbC15 ("pure" grade) was used without further purification. The copolymerization was carried out in a four-necked vessel provided with a stirrer and thermometer. Before introducing the components the vessel was evacuated and filled with argon; the reactants were placed in the vessel in an argon current. The molar ratio of THF to PO was 3.33 in all the experiments. The catalyst was added, while stirring, to a mixture of the reactants that had been cooled to -- 30°, and the temperature was then raised to 0 ° over a 15-rain period. Stirring was stopped after rapid heat liberation had ceased, and the polymerizate was kept at 0 ° for 48 hr. By introducing the catalyst at --30 ~ it was possible to control the copolymerization temperature and avoid overheating, thereby ensuring the reporoducibility of the results. The separation of the product was effected by using the procedure outlined in [4]. The molecular weights of the oligomers were determined by measuring the heats of condensation ( ~ ) [13] and by hromination of terminal unsaturated groups (11~). To determine the amount of allyl and isopropenyl groups in the products of T H F - P O copolymerization, the possible formation of which was reported in [14], the monomers were copolymerized in the presence of acetic anhydride used as the chain transfer agent. The concentration of the latter was 0.1492 and 0.912 mole/1. Determination of the unsaturation of the resultant diacetates did not show the presence of double bonds in the products. The synthesized oligomers were liquids of different viscosities depending on the molecular weight, and were soluble in many organic solvents; during the polymerization they became insoluble network polymers. DISCUSSION OF RESULTS
A s t u d y was m a d e of the e x t e n t to which the conditions of T H F - P O c o p o l y m e r i z a t i o n in the presence of M_A, with SbC15 as catalyst, influenced the yield a n d molecular w e i g h t o f the products. As the time of the c o p o l y m e r i z a t i o n process was increased the o l i g o m e r yield rose, reaching a c o n s t a n t value (~55°/o) in 10 hr (Fig. 1). The r e l a t i v e l y low yields m a y be due to partial d e c a y of the active centres owing t o true t e r m i n a t i o n o f the growing chain. This is s u p p o r t e d b y the presence of chlorine in t h e products. The curves of ~tln a n d J l ~ / / l ~ vs. reaction time h a v e a m a x i m u m in a r o u n d 2 - 4 h r (Fig. 1). ~ , a n d / ~ of the oligomers are n o t equal, the value o f ~ generally being considerably higher t h a n Jl4~, which is a t t r i b u t a b l e to s u b s t a n c e s with e n d g r o u p s c o n t a i n i n g n o double b o n d s being p r e s e n t in the reaction p r o d u c t s .
2076
L.N.
TUROVSKAYA e$ a/.
•fO-3
J
8g
o-.--
2"5i
6" 40 2 a~-- i/¢
0"5
2I Z~
I
~e 7"~me,hr
72
FiG. 1. Plots of the yield (1), molecular weights ~ ' (2), and il~ of the oligomers (3) and the .,V4~'/~l~, ratio (4) vs. reaction time at 0°; T H F : PO ----3.33; SBC16----0.34;[MA] ~0.576 mole. Here and in Figs. 2-4 T H F = 0 . 1 9 7 2 , PO~0.0592 mole.
An inadequate number of functional groups as well as an extremal type of relationship found on plotting/11~ against reaction time was noted in [15-20] by authors investigating the polymerization and copolymerization of some heterocyclic monomers. a Ili7~,
a-
IZ ~
5 •
3 j
J
2 x..]
I
0
a
•
I
8 5 2
7
i
J
O.f
i
I
i 1.2
i
0
0.~
0"8
/'2[HAling/gill
FIG. 2. Plots of 1 / / ~ (a) and l / ~ ' ( b ) vs MA concentration; SbC15× 103~1"25 (1), 2.5 (2), 5 (3), 7.81 (d) and 10 moles (5). Here and in Figs. 3 and 4 the reaction time is 48 hr; 0 °.
Copolymerization of tetrahydrofuran with propylene oxide
2077
The Mn-values of the oligomers are inversely proportional both to MA concentration (Fig. 2) and to catalyst concentration (Fig. 3). The linearity of the 1/Mn vs. SbC15 plot is likewise preserved in the case of zero MA concentration. The values of 1 / ~ for [MA]----0 were obtained, by extrapolation, from Fig. 2.
b
lO
a
o
i 0.2
I 0"4
[SbC 5],
0
V -
[ 0"2
I
0"4, [SbC'~],mo/e//.
FIG. 3. Plots of 1 / ~ (a) and 1 / ~ ' (b) vs. catalyst concentration; MA × 103=33.5 (•); 19.95 (2) 13.26 (3); 2-76 (4) and 0 mole (5). The ~ / / l ~ ratio is reduced as the [MA]/[SbC15] ratio increased but a limiting molecular wt. ratio appears at particular values of the concentrations which are dependent on SbCl~ concentration. The limiting values of M~/114~ reduce with increasing catalyst concentration, and approach unity when the latter is high (Fig. 4). According to present-day ideas with regard to the mechanism of cationic polymerization of cyclic ethers in the presence of chain transfer agents [21, 22] MA taken in excess relative to catalyst will participate both in initiation, and in chain transfer, and will determine the nature of the endgroups. However, it is known that in cationic polymerization and copolymerization PO is capable of forming active centres without the participation of the cocatalyst [23-25]. I n this case chain termination reactions, namely cyclization involving catalyst
2078
L. N. TuRovs~YA et a/.
reactivation [26] and termination on gegen-ions by addition of anion residues (e.g. chloride) at the end of the molecule will lead to the formation of nonfunctional or chlorine-containing products.
I o
I B
,~l 16
t zO
FIG. 4. Change in the ~ ' / ~ ' ratio vs. molar ratio ofMA : SbCls; SbCI~= 103= 10 (•); 7.81 (2), 5 (3); 2-5 (4) and 1.25 mole (5). In the case of T H F - P O copolymerization the amount of nonfunctional compounds is apparently determined largely by the ratio of active centres formed at the stage of initiation both with and without the participation of MA, as well as by the occurrence of chain termination reactions, as a result of which nonfunctional oligomers are formed, in other words, other conditions being identical, the amount of nonfunctional compounds will depend on the P O : M A ratio. When the catalyst is added to the mixture of monomers and chain transfer agent at the start of the reaction, the PO concentration greatly exceeds the MA concentration, which favours the formation of active centres without the participation of MA. On increasing the amount of the latter, the probability of MA participating in the formation of active centres is increased, and this, along with chain transfer to anhydride and chain transfer accompanied by termination will in tote increase the amount of products with terminal methacrylate groups. Translated by R. J. A. H~ND~Y
REFERENCES
1. A. M. EASTMAN, Fortsch. Hochpol. Forsch. 2: 18, 1960 2. L. A. DICKISON, J. Polymer Sci. 58: 857, 1962 3. A. A. BERLIN, N. G. MATVEYEVA, E. S. MA_MEnOVA, E. S. PAPKOVA and L. M.
VOLK0VA, U.S.S.R. Pat. No. 191798, 1966; ByulL izob., No. 4, 1967 4. A. A. BERLIN, N. G. MATVEYEVA and E. S. PANKOVA, Vysokomol. soyed. A9: 1325, 1967 (Translated in Polymer Sei. U.S.S.R. 9: 6, 1485, 1967)
Copolymorization of tetrahydrofuran with propylene oxide
2079
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