- Email: [email protected]
The relationship between the molecular weight and intrinsic viscosity of stereoregular polymethylmethacrylate fractions in benzene
THE RELATIONSHIP BETWEEN THE MOLECULAR WEIGHT AND INTRINSIC VISCOSITY OF STEREOREGULAR POLYMETHYLMETHACRYLATE FRACTIONS IN BENZENE* V. ~(. TSVETKOV, V. S. SKAZKA a n d N. M. KRIVORUCHKO Institute of Physics, Leningrad State University. Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences
(Received 19 March 1960)
THE study of the relationship between the molecular weight M and intrinsic viscosity [t/] of solutions of stereoregular polymers has been the subject of more than one investigation [1, 2, 3]. The materials studied were stereoisomers of polystyrene [I, 3] and polypropylene [2]. The experimental work brought to light no differences in the relationship [t/]-----f(M) for the isotactic and atactic stereoisomers, indicating that the stereoregularity of the molecular chains has no effect on their hydrodynamic dimensions in solution. A certain difficulty in the comparison of the results obtained for the atactic and isotactic samples is the relatively poorer solubility of the latter, which in principle cannot but have some bearing on the dimensions of their molecules in solution. The opinion has even been expressed that the relationship between the dimensions of the "backbone" of the molecules and the stereospecificity of their structure, which actua]ly exists, is ow~rshadowed by volume effects (i.e. interaction with the solvent). In this connection it seemed of value to carry out a similar investigation with polymers which, while having a stereoregular structure, at the same time have fairly good solubility in comparison with the atactic stereoisomers. Stereoregular polymethy]methacrylate (PMMA), which possesses such proFerties, served as the object of the present investigation. MATERIALS AND METHOD
Stereoregular polymethylmethacrylate was prepared by A. A. Korotkov and his collaborators 4 by homogeneous catalytic polymerization at low temperatures (--50 to --60 °) in the presence of all organo-metullie catalyst. We investigated two samples the first of which had been polymerized in a nnutral medium (toluene) and the second in an alkaline medium (liquid ammonia). From the method of preparation and also from the observed properties [5, 6] the first PMMA sample had the iso~actic structure and the second the syndiotactic. * Vysokomol. soedin. 2: No. 7, 1045-1048, 1960. 1~;*
229
230
V.N. TSVETKOVet al.
Both polymers were readily soluble in organic solvents. The two samples were fractionated, the isotaetic material into 8 fractions and the stereoisomer into 11 fractions. Fractionation was achieved by fractional precipitation from benzene solution. The precipitants used were hexane (isotactic PMMA) and petroleum ether (syndiotactic PMMA). When necessary the solutions were heated for prolonged periods to ensure complete solution of the polymers. Measurements were made at room temperature. Particular attention was paid to testing the optical purity and molecular dispersion of the solutions. The absence of colloidal material (undissolved crystallites, catalyst residues etc.) was established by special measurements of the electrical birefringence, degree of depolarization and asymmetry of light scattering of the solutions. Final purification of the solutions was carried out b y centrifuging in a field of about 30,000g. In all cases this treatment gave completely satisfactory results. EXPERIMENTAL
The molecular weights of the stereoregular PMMA fractions were determined b y the light scattering of their solutions in acetone and ethyl acetate in a spherical, visual nephelometer [7]. I t was found that the solutions of the fractions of both isotactic and syndiotactic PMMA exhibit no light-scattering dissymetry indices (Fig. 1.). Consequently the measurements were made at
!"0
o
o
?
~
o
ol o20
0
I
J
Q;~"
}0
sin 0/2
FI(~. 1. The angular dependence of the inverse light-scattering intensity I o for solutions of three fractions of isotac~ic (1) and syndiotactie (2) PMMA in acetone, C=0.42 and 0.16~ per cent respectively. a scattering angle of 0-~90 °. Examples of the dependence of c/R'oo (c is the concentration of the solution and R~0 the excess scattering of the solution over that of the solvent at 0 = 9 0 °) on c are given in Figure 2. The molecular weights, M, obtained b y extrapolation of the straight lines of Figure 2 to c-, 0, are given in Table 1. The second virial coefficients of the solutions, A2, found from the slopes of the lines, are also given. Viseometric measurements on solutions of the PMMA fractions were carried out with ordinary Ostwaldt viscometers with effiux times for 7cm a of solvent of 97.2 and 289secs. Benzene was used as solvent in these experiments. Because of the low molecular weights of the fractions investigated the intrinsic viscosities,
Molecular w e i g h t
and
i n t r i n s i c v i s c o s i t y of s t e r c o r e g u l a r
p o l y m e t h y l m e t h a c r y l a t e 231
TABLE 1. MOLECULAR, WEIGHTS OF FRACTIONS OF ISO- AND SYNDIOTACTIC P M M A , TI~E VIRIAL COEFFICIENTS A.~ AND THE INTR,INSIC VISCOSITIES [vii OF THEIR, SOLUTION IN BENZENE
Polymer
Isotactic PMMA
Syndiotactie PMMA
Fraction
III
IV
VI
VII
VIII
2
M × 1 0 -5 A~x104
3.20 1.50 0.82
2.00
1.55
1.10 1.87 0.37
0.60 2.58 0.28
4.50 1.50 0.96
3
4
5
7 !
~,/
--
--
0.58
0.48
3.00 1.50 0.66
1.30 1.50 0.37
0.50 I 0.30 2.70 ! 4.00 0.165i] 0.124
/ ]
o.:
c •
5
7/;,,';
VII;
7t)L~~ 7)? ~
1.0
Yl! 4
f~
/7
,q,.
~.};
t~
1 t.5-/,"
:,
05
!.0
O
fl
V/I/
I
1.5 c, %
FIG. 3. T h e d e p e n d e n c e of ~lsp/C o n c for solutions of f r a c t i o n s of isotac~ic (a) a n d s y a d i o t a c t i c (b) P M M A in b e n z e n e . T h e figures indicate t h e f r a c t i o n n u m b e r s .
FIG. 2. D e p e n d e n c e of c/R'go o n c for s o l u t i o n s o f some f r a c t i o n s of i s o t a e t i c (a) a n d s y n d i o t a e t i e (b) P M M A i n acetone. T h e figures indicate the fraction numbers.
[r/], m e a s u r e d in the two viscometers are in good agreement. T h e dependence o f ~plc on c o n c e n t r a t i o n c fits the e q u a t i o n ~sp -
-
-[r/]-÷k'[~]2c
¢
fairly accurately, with k' ~ 0.4, which is normal for solutions of linear p o l y m e r s in good solvents (Fig. 3.). The intrinsic viscosities of the fractions investigated are given in the table.
232
V.N. TSVETKOVet
al.
DISCUSSION
Figure 4 shows the relationship between intrinsic viscosity and molecular weight of the PMMA fractions in benzene, plotted on a log-log scale. The graph coincides with the relationship found previously 8 for solutions of atactic PMMA, expressed alalytical]y b y the equation: [7]--0.468 × 10-4 × M °'7~ The points represent the experimental values of M and [7] found for isotactic (white circles) and syndiotactic (black circles) PMMA in the present investigation. ~,5
50
v,t y V ' Z~ '&~
55 _,,, ~og
oa
tog/YT~ FI6. 4. The dependence of log [~] on log M for solutions of fractions of isotactic (a) and syadiotactic (b) PMMA in benzene. The numbers indicate the fraction numbers. The straight line represents a relatinnship similar to that for atactic PMMA [8]. Within the limits of experimental error the points are grouped about a straight line. Hence the relationship between M and [7] for the stereoregular samples in benzene practically coincides with the similar relationship for the atactic polymer. This means that the hydrodynamic dimensions of the PMMA macromolecule in benzene are independent of the stereospecific nature of the polymer. Comparison of the second virial coefficients of the fractions, given in the table, with the values found previously [8] for fractions of atactic PMMA of corresponding molecular weight, shows that the values of A S coincide for all the stereoisomers. Hence it m a y be supposed that interaction with the solvent (volume effects) alters the "backbone" dimensions of the molecules of both the stereoregular and atactic polymers equally. Hence on the basis of these results the conclusion m a y be drawn that stereoregularity in PMMA chains has practically no effect on their unperturbed dimensions. The authors are grateful to A. A. Korotkov and S. P. Mitsengendler for providing the samples of PMMA.
1-[omopolymerization and copolymerization of isoprene initiated by
ethyllithium 233
CONCLUSIONS
(1) The light scattering of a number of fractions of iso- and syndiotactic PMMA in acetone and ethyl acetate has been investigated and the intrinsic viscosities of these fractions in benzene have been determined. It was shown that over the range of molecular weights studied (0.3 × 105-4.5 × 10~) the dependence of intrinsic viscosity on molecular weight is the same for all the stereoisomers. (2) On the basis of these results the conclusion m a y be drawn that stereoregularity in PMMA chains has practically no effect on their unperturbed dimensions. Translated by E. O. PHILLIPS REFERENCES 1. G. NATTA and P. CORRIADINI, Makromol. Chem. 16: 77, 1955 2. F. DANUSSO and G. MORAGLIO, Makromol. Chem. 28: 250, 1958 3. W. R. KRIGBAUM, D. K. CARPENTER and S. NEUMANN, J. Phys. Chem. 62: 1586, 1958 4. A. A. KOROTKOV, S. P. MITSENGENDLER, V. N. KRASULINA and L. A. VOLKOVA, Vysokomol. soedin. 1: 1319, 1959 5. T. G. FOX and W. E. GOODE, J. Polymer Sei. 31 : 173, 1958 6. W. E. GOODE, Gordonovskaya konferentsiya. (Gordon Conference.) 1958 7. V. N. TSVETKOV and V. S. SKAZKA, Optika i spektroskopiya 7: 808, 1959 8. V. N. TSVETKOV, K. Z. FATTAKHOV and O. V. KALLISTOV, Zh. eksp. teor. fiz. 26: 345, 1954
THE HOMOPOLYMERIZATION
AND COPOLYMERIZATION
OF ISOPRENE INITIATED BY ETHYLLITHIUM* YU. L. S P I R I N , D. K. P O L Y A K O V , A. R. GANTMAKHER and S. S. MEDVEDEV L. Ya. K a r p o v Physicoehemical Institute
(Received 17 March 1960)
1N a previous paper [1] it was shown that the mechanism of polymerization of styrene b y ethyllithium is changed considerably on passing from a hydrocarbon solvent to a mixture of triethylamine and toluene, and the mechanism of polymerization in the presence of organolithium compounds was examined. * Vysokomol. soedin. 2: No. 7, pp. 1082-1092, 1960.
(Received 19 March 1960)
THE study of the relationship between the molecular weight M and intrinsic viscosity [t/] of solutions of stereoregular polymers has been the subject of more than one investigation [1, 2, 3]. The materials studied were stereoisomers of polystyrene [I, 3] and polypropylene [2]. The experimental work brought to light no differences in the relationship [t/]-----f(M) for the isotactic and atactic stereoisomers, indicating that the stereoregularity of the molecular chains has no effect on their hydrodynamic dimensions in solution. A certain difficulty in the comparison of the results obtained for the atactic and isotactic samples is the relatively poorer solubility of the latter, which in principle cannot but have some bearing on the dimensions of their molecules in solution. The opinion has even been expressed that the relationship between the dimensions of the "backbone" of the molecules and the stereospecificity of their structure, which actua]ly exists, is ow~rshadowed by volume effects (i.e. interaction with the solvent). In this connection it seemed of value to carry out a similar investigation with polymers which, while having a stereoregular structure, at the same time have fairly good solubility in comparison with the atactic stereoisomers. Stereoregular polymethy]methacrylate (PMMA), which possesses such proFerties, served as the object of the present investigation. MATERIALS AND METHOD
Stereoregular polymethylmethacrylate was prepared by A. A. Korotkov and his collaborators 4 by homogeneous catalytic polymerization at low temperatures (--50 to --60 °) in the presence of all organo-metullie catalyst. We investigated two samples the first of which had been polymerized in a nnutral medium (toluene) and the second in an alkaline medium (liquid ammonia). From the method of preparation and also from the observed properties [5, 6] the first PMMA sample had the iso~actic structure and the second the syndiotactic. * Vysokomol. soedin. 2: No. 7, 1045-1048, 1960. 1~;*
229
230
V.N. TSVETKOVet al.
Both polymers were readily soluble in organic solvents. The two samples were fractionated, the isotaetic material into 8 fractions and the stereoisomer into 11 fractions. Fractionation was achieved by fractional precipitation from benzene solution. The precipitants used were hexane (isotactic PMMA) and petroleum ether (syndiotactic PMMA). When necessary the solutions were heated for prolonged periods to ensure complete solution of the polymers. Measurements were made at room temperature. Particular attention was paid to testing the optical purity and molecular dispersion of the solutions. The absence of colloidal material (undissolved crystallites, catalyst residues etc.) was established by special measurements of the electrical birefringence, degree of depolarization and asymmetry of light scattering of the solutions. Final purification of the solutions was carried out b y centrifuging in a field of about 30,000g. In all cases this treatment gave completely satisfactory results. EXPERIMENTAL
The molecular weights of the stereoregular PMMA fractions were determined b y the light scattering of their solutions in acetone and ethyl acetate in a spherical, visual nephelometer [7]. I t was found that the solutions of the fractions of both isotactic and syndiotactic PMMA exhibit no light-scattering dissymetry indices (Fig. 1.). Consequently the measurements were made at
!"0
o
o
?
~
o
ol o20
0
I
J
Q;~"
}0
sin 0/2
FI(~. 1. The angular dependence of the inverse light-scattering intensity I o for solutions of three fractions of isotac~ic (1) and syndiotactie (2) PMMA in acetone, C=0.42 and 0.16~ per cent respectively. a scattering angle of 0-~90 °. Examples of the dependence of c/R'oo (c is the concentration of the solution and R~0 the excess scattering of the solution over that of the solvent at 0 = 9 0 °) on c are given in Figure 2. The molecular weights, M, obtained b y extrapolation of the straight lines of Figure 2 to c-, 0, are given in Table 1. The second virial coefficients of the solutions, A2, found from the slopes of the lines, are also given. Viseometric measurements on solutions of the PMMA fractions were carried out with ordinary Ostwaldt viscometers with effiux times for 7cm a of solvent of 97.2 and 289secs. Benzene was used as solvent in these experiments. Because of the low molecular weights of the fractions investigated the intrinsic viscosities,
Molecular w e i g h t
and
i n t r i n s i c v i s c o s i t y of s t e r c o r e g u l a r
p o l y m e t h y l m e t h a c r y l a t e 231
TABLE 1. MOLECULAR, WEIGHTS OF FRACTIONS OF ISO- AND SYNDIOTACTIC P M M A , TI~E VIRIAL COEFFICIENTS A.~ AND THE INTR,INSIC VISCOSITIES [vii OF THEIR, SOLUTION IN BENZENE
Polymer
Isotactic PMMA
Syndiotactie PMMA
Fraction
III
IV
VI
VII
VIII
2
M × 1 0 -5 A~x104
3.20 1.50 0.82
2.00
1.55
1.10 1.87 0.37
0.60 2.58 0.28
4.50 1.50 0.96
3
4
5
7 !
~,/
--
--
0.58
0.48
3.00 1.50 0.66
1.30 1.50 0.37
0.50 I 0.30 2.70 ! 4.00 0.165i] 0.124
/ ]
o.:
c •
5
7/;,,';
VII;
7t)L~~ 7)? ~
1.0
Yl! 4
f~
/7
,q,.
~.};
t~
1 t.5-/,"
:,
05
!.0
O
fl
V/I/
I
1.5 c, %
FIG. 3. T h e d e p e n d e n c e of ~lsp/C o n c for solutions of f r a c t i o n s of isotac~ic (a) a n d s y a d i o t a c t i c (b) P M M A in b e n z e n e . T h e figures indicate t h e f r a c t i o n n u m b e r s .
FIG. 2. D e p e n d e n c e of c/R'go o n c for s o l u t i o n s o f some f r a c t i o n s of i s o t a e t i c (a) a n d s y n d i o t a e t i e (b) P M M A i n acetone. T h e figures indicate the fraction numbers.
[r/], m e a s u r e d in the two viscometers are in good agreement. T h e dependence o f ~plc on c o n c e n t r a t i o n c fits the e q u a t i o n ~sp -
-
-[r/]-÷k'[~]2c
¢
fairly accurately, with k' ~ 0.4, which is normal for solutions of linear p o l y m e r s in good solvents (Fig. 3.). The intrinsic viscosities of the fractions investigated are given in the table.
232
V.N. TSVETKOVet
al.
DISCUSSION
Figure 4 shows the relationship between intrinsic viscosity and molecular weight of the PMMA fractions in benzene, plotted on a log-log scale. The graph coincides with the relationship found previously 8 for solutions of atactic PMMA, expressed alalytical]y b y the equation: [7]--0.468 × 10-4 × M °'7~ The points represent the experimental values of M and [7] found for isotactic (white circles) and syndiotactic (black circles) PMMA in the present investigation. ~,5
50
v,t y V ' Z~ '&~
55 _,,, ~og
oa
tog/YT~ FI6. 4. The dependence of log [~] on log M for solutions of fractions of isotactic (a) and syadiotactic (b) PMMA in benzene. The numbers indicate the fraction numbers. The straight line represents a relatinnship similar to that for atactic PMMA [8]. Within the limits of experimental error the points are grouped about a straight line. Hence the relationship between M and [7] for the stereoregular samples in benzene practically coincides with the similar relationship for the atactic polymer. This means that the hydrodynamic dimensions of the PMMA macromolecule in benzene are independent of the stereospecific nature of the polymer. Comparison of the second virial coefficients of the fractions, given in the table, with the values found previously [8] for fractions of atactic PMMA of corresponding molecular weight, shows that the values of A S coincide for all the stereoisomers. Hence it m a y be supposed that interaction with the solvent (volume effects) alters the "backbone" dimensions of the molecules of both the stereoregular and atactic polymers equally. Hence on the basis of these results the conclusion m a y be drawn that stereoregularity in PMMA chains has practically no effect on their unperturbed dimensions. The authors are grateful to A. A. Korotkov and S. P. Mitsengendler for providing the samples of PMMA.
1-[omopolymerization and copolymerization of isoprene initiated by
ethyllithium 233
CONCLUSIONS
(1) The light scattering of a number of fractions of iso- and syndiotactic PMMA in acetone and ethyl acetate has been investigated and the intrinsic viscosities of these fractions in benzene have been determined. It was shown that over the range of molecular weights studied (0.3 × 105-4.5 × 10~) the dependence of intrinsic viscosity on molecular weight is the same for all the stereoisomers. (2) On the basis of these results the conclusion m a y be drawn that stereoregularity in PMMA chains has practically no effect on their unperturbed dimensions. Translated by E. O. PHILLIPS REFERENCES 1. G. NATTA and P. CORRIADINI, Makromol. Chem. 16: 77, 1955 2. F. DANUSSO and G. MORAGLIO, Makromol. Chem. 28: 250, 1958 3. W. R. KRIGBAUM, D. K. CARPENTER and S. NEUMANN, J. Phys. Chem. 62: 1586, 1958 4. A. A. KOROTKOV, S. P. MITSENGENDLER, V. N. KRASULINA and L. A. VOLKOVA, Vysokomol. soedin. 1: 1319, 1959 5. T. G. FOX and W. E. GOODE, J. Polymer Sei. 31 : 173, 1958 6. W. E. GOODE, Gordonovskaya konferentsiya. (Gordon Conference.) 1958 7. V. N. TSVETKOV and V. S. SKAZKA, Optika i spektroskopiya 7: 808, 1959 8. V. N. TSVETKOV, K. Z. FATTAKHOV and O. V. KALLISTOV, Zh. eksp. teor. fiz. 26: 345, 1954
THE HOMOPOLYMERIZATION
AND COPOLYMERIZATION
OF ISOPRENE INITIATED BY ETHYLLITHIUM* YU. L. S P I R I N , D. K. P O L Y A K O V , A. R. GANTMAKHER and S. S. MEDVEDEV L. Ya. K a r p o v Physicoehemical Institute
(Received 17 March 1960)
1N a previous paper [1] it was shown that the mechanism of polymerization of styrene b y ethyllithium is changed considerably on passing from a hydrocarbon solvent to a mixture of triethylamine and toluene, and the mechanism of polymerization in the presence of organolithium compounds was examined. * Vysokomol. soedin. 2: No. 7, pp. 1082-1092, 1960.