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The compositional and molecular weight inhomogeneity of N-vinylpyrrolidone-vinyl acetate copolymers
Weight inhomogeneity of N-vinylpyrrolidone-vinyl acetate copolymers
2979
polyurethane with the best properties is formed in solution in tetramethylenesulphone. (2) The molecular weights of the polyurethanes were detmrmlned by the light scattering method and the intrinsic viscosities were measured in dimethylformamide. It was found that [7]----5"4 x 10-4 Mo~~4. (3) The chain flexibility of the polyurethanes was studied. It is shown that increase in the con~ntration of urethane groups in the chain leads to considerable increase in its rigidity. Trandated by E. O. P--T~.T,UeS REFERENCES 1. 2. 3. 4. 5. 6. 7.
O. BAYER, Angew. Chem. 59: 257, 1947 D. J. LIMAN, J. Polymer Sci. 45: 49, 1960 M. E. BAILEY, V. KIRSS and R. G. SPAUNBURGH, Ind. Engng. Chem. 48: 794, 1956 V. Ye. ESKIN, Zh. tekh. fiz. 28: 1459, 1958 A. Ye. NESTEROV and Yu. S. LIPATOV, Vysokomol. soyed. BP: 695, 1967 W. H. STOCKMAYER and M. FIXMAN, J. Polymer Sci. C1: 137, 1963 V. Ye. ESKIN, Uspekhi fiz. nauk 82: 649, 1964
THE COMPOSITIONAL AND MOLECULAR WEIGHT INHOMOGENEITY OF N-VINYLPYRROL1DONE-VINYL ACETATE COPOLYMERS* V. A. AGASAIWDYAI~, L. G. KUDRYAVTSEVA, A. D. LITI~IAIWOWICH and V. VA. SHTERI~ A. V. Topchiev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences (Received 7 December 1966)
COPOLYMERS of N-vinylpyrrolidone (VP) with vinyl acetate (VA) can be used as starting materials for the preparation of medical products based on copolymers, i.e. for the production of blood substitutes [1]. For the preparation of such products it is very essential that the original copolymer should be sufficiently uniform in both composition and molecular weight. The most general method for preparation of copolymers of uniform composition is by synthesis in a continuous flow reactor with adequate stirring [2]. A copolymer prepared under these conditions should also have a narrower molecular weight distribution than copolymers prepared under static conditions [3]. * Vysokomol. soyed. AP: No. 12. 2634-2636, 1967.
2980
V . A . AGASANDYA3~Teg o~.
I n this w o r k the compositional a n d molecular weight i n h o m o g e n e i t y o f t w o samples of V P - V A copolymers were compared, one o f which was p r e p a r e d in a c o n t i n u o u s r e a c t o r a n d the o t h e r u n d e r static conditions. The t w o samples were p r e p a r e d a t fairly high a n d almost identical degrees of conversion a n d t h e average mole fractions o f V P in t h e c o p o l y m e r (~) a n d the intrinsic viscosities ([~/]) were v e r y similar.
EXPERIMENTAL The batch-process copo]yiner was prepared in solution in isopropanol in an atmosphere of nitrogen at 70° with polymerization time of 1'5 hr. The concentration of the monomer mixture in the solution was ~ 24~o by volume, the molar composition of the initial monomer mixture was VP:VA=0"32:0"68 and the initial concentration of azobisisobutyronitrile was 10-z mole/1, of monomer mixture. The conditions of preparation in the continuous reactor and the methods of purification of the reagents and isolation of the copolymers were described in reference [4]. The average characteristics of the eopolymers were: a) in the continuous reactor, conversion 69"5% by weight ,[~/]=0"11 cU/g, ==0"53; b) under static conditions, conversion 68"2~o by weight, [~/]----0"12 dl/g, ==0"525.
7~
0"5
i
1
i
o~
I
l'O
FIG. 1. Dependence of the precipitation threshold (~*) on copolymer composition (=) for the systems: 1--dJethyl ether-~cetone, 2--n-hexane-isopropanol. For characterization of the compositional and molecular weight inhomogeneity of the copolymers we used the method of cross fractionation [5]. This method was chosen because it is more e~Rcient than successive precipitation or branched fractionation [6, 7]. The most efficient preclpitant-solvent system for cross fraetionation was chosen on the basis of a study of the dependence of the precipitation threshold y* (the volume fraction of the precipitant in the solution at the moment of appearance of turbidity) on the copolymer composition ~. In conformity with the requirements of the method of selection of a precipitanf~solvent system for fractionation of copolymers [8] the dependence of y* on = was studied
Weight inhomogeneity of N-vinylpyrrolidone-vinyl acetate copolymers ~EAN
2981
COMPOSITIONS (~) AND I N T R I N S I C VISCOSITIES ([11]) OF FRACTIONS OF COPOLYMERS
rR~PA~ED I~ A co~ri~vovs
Characteristic
A~D V I ~ D E R STATIC C O ~ D m O N S
m
a
b C
d
[,1]
REAC~O~ ( ~ A T O ~ ) (D~NOm~ATOR)
a
b C
d
0.530/0.515 0.555/0.630 0.555/0.650 0.535/0.625 0.150/0.200 0.135/0.200 0.130/0.155 0.110/0.125
0-530/0'430 0.530/0"480 0.530/0"515 0"545/0"590 0"125/0"120 0"115/0"110 0.110/0.105
0.085/0.090
0.510/0'335 0.530/0.410 0.530/0.465 0.520/0.505 0"090/0"080 O.O9O/O"O75 0.085/0.075 O'O7O/O'O5O
with copolymers of fairly high molecular weight (10 s) a n d uniformity of composition prepared b y copolymerization to a conversion of 2 - 3 % . F r o m the results of preliminary experiments we selected the systems diethyl e t h e r acetone and n-hexane-isopropanol for the fractionation. I t is seen from Fig. 1 t h a t in the region of ~~ 0.5, in which we are interested, in the first system 7* falls fairly r a p i d l y a n d in the second system rises with increase in ~. This pair of systems therefore satisfy the requirements of the cross fractionation method. The copolymers were first separated into three fractions in the ether-acetone system, then each of these fractions was further fractionated in the n-hexane-isopropanol system. Fractionation was carried out at 24 ° in accordance with the generally adopted m e t h o d [9]. All the fractions were reprecipitated from solution in isopropanol b y ether and the precipitates were dissolved in water a n d freeze-dried. The intrinsic viscosity (It/I) was determined in water a t 25 °. The composition of t h e fractions was determined with t h e a i d of an I T R - 2 interferometer. All the measurements were m a d e in solution in methanol at a concentration of 0"01 g/cm 8 a t 20 °. The difference between the refractive indices (R) in solutions of VP and VA homopolymers is zfR= 7"4 × 10 -~. The copolymer composition was determined from the value of R, assuming a linear relationship between the composition of the copolymer a n d refractive index. The relative error in determination of the composition of the fractions was 4-3~o. D a t a on the composition and intrinsic viscosity of the fractions are given in t h e Table (where n = 1-3 are the code numbers of the initial fractions and m - - a - d the numbers of t h e final fractions). RESULTS AND DISCUSSION
Curves of the integral composition distribution (I~) of the copolymers prepared in the continuous reactor and by the batch process were constructed from the data in the Table (Fig. 2). The I~ curves were constructed on the basis of the usual assumption that overlapping of the differential composition distribution curves for the fractions is small [6]. For estimation of the molecular weight inhomogeneity of the copolymers we used the integral (I[~]) and differential (W[~]) intrinsic viscosity distribution
V. A. AGASANDYANe~ a~.
2982
curves, because there are no data available on the relationship between [t/] and molecular weight for V P - V A copolymers. The I[,] and WE,1 curves were constructed b y the method of Tung [10] (Fig. 3).
11 0
1"01
011
03
~
i
Oq
I
05
0.6
I
O~7cz
O~l
FIG. 2
0"2
[~]
Fm. 3
Fro. 2. Integral composition distribution curves for VP-VA copolymers prepared in a continuous reactor (1) and under static conditions (2). Fzo. 3. Integral (I[~]) and differential (W[~])intrinsic viscosity distribution curves for VP-VA copolymers prepared in a continuous reactor (1, 1") and under static conditions (2, 2'). I t is seen from Figs. 2 and 3 that the copolymer prepared in the continuous reactor is considerably more homogenous with respect to composition and molecular weight than the sample prepared b y the batch method. CONCLUSIONS
A study has been made of samples of a copolymer of N-vinylpyrrolidone and vinyl acetate prepared in a continuous reactor with ideal mixing and under static conditions to a degree of conversion of 70% b y weight, and having the same average characteristics (intrinsic viscosity and composition). I t is shown b y means of cross fractionation that the sample prepared in the continuous reactor is considerably more homogenous with respect to composition and molecular weight than the sample prepared under static conditions. Trana/ate~ by E. O. pwrrm~ps REFERENCES
1. S. N. USHAKOV, Sinteticheskie polimery lekarstvennogo naznacheniya (Synthetic Polymers for Medical Purposes). Medgiz, 1962 2. F. T. WALL, C. J. DELBECK and R. E. FLORIN, J. Polymer Sei. 9: 177, 1952
]:)epolymerization of polypropylene during inhibited oxidation
2983
3. K. G. DENBIGH, Trans. F a r a d a y Soc. 43: 648, 1947 4. V. A. AGASANDYAN, A. D. L1TMANOVICH a n d V. Ya. SHTERN, K i n e t i k a i kataliz 8: 773, 1967 5. A. I. ROSENTHAL a n d B. B. WHITE, I n d Engng. Chem. 44: 2693, 1952 6. A. D. LITMANOVICH and V. Y a . SHTERN, International Symposium on Macromolecular Chemistry, P r e p r i n t 130, Prague, 1965 7. L. G. KUDRYAVTSEVA and A. I). LITMANOVICH, Vysokomol. soyed. A9: 18, 1967 8. A. D. LITMANOVICH, Dissertation, 1963 9. P. W. ALLEN, Metody issledovaniya polimerov (Techniques of Polymer Characterization). Foreign Literature Publishing House, 1961 (Russian translation) I0. L. H. TUNG, J. Polymer Sci. 29: 495, 1956
INVESTIGATION OF THE DEPOLYMERIZATION OF POLYPROPYLENE DURING THE COURSE OF INHIBITED OXIDATION* B. A. GROMOV and Yu. A. SHLYAPNIKOV Chemical Physics Institute, U.S.S.R. A c a d e m y of Sciences.
(Received 10 December 1966)
h ' HAS been shown [1] that, during the induction period in the inhibited oxidation of polyolefins, changing quantities of low molecular olefins are formed; these are the products of the depolymerization of aliphatic maeroradicals. Thus the rate of formation of a specific olefin should be proportional to the concentration of macroradicals with a certain structure with a free valency at the end of the polymer chain, and m a y serve as a measure of the concentration of such radicals. Clearly, the break-away of hydrogen atoms from a sufficiently large macromolecule, taking place according to "the law of chance", will lead predominantly to the formation of macro-radicals with the free valency in the middle of the polymer chain, and therefore, in studying the formation of olefins, one should watch out for radicals with a "secondary" mode of origin. EXPERIMENTAL Isotactic polypropylene with an intrinsic viscosity of [~/]=3"1 (tetralin, 135 °C), purified as described in reference [2], was used in this work. The inhibitors, namely, 2,4,6-tritert.butylphenol, melting point 132 °C a n d 2,2'-methylene-bis-(4-methyl-6-tert.butylphenol), melting point 126 °C, were purified b y distillation in vacuum. The specimens of polypropylene containing the inhibitor were heated in sealed ampoules in an oxygen atmosphere for a given time; after being cooled, the gases contained in the ampoule were expelled b y water into a syringe and then introduced into the chromatograph (silica-gel; 90 cm; 60°C; carrier gas-hydrogen, 20 ml/min; flame-ionization detector). * Vysokomol. soyed. Ag: No. 12, 2637-2640, 1967.
2979
polyurethane with the best properties is formed in solution in tetramethylenesulphone. (2) The molecular weights of the polyurethanes were detmrmlned by the light scattering method and the intrinsic viscosities were measured in dimethylformamide. It was found that [7]----5"4 x 10-4 Mo~~4. (3) The chain flexibility of the polyurethanes was studied. It is shown that increase in the con~ntration of urethane groups in the chain leads to considerable increase in its rigidity. Trandated by E. O. P--T~.T,UeS REFERENCES 1. 2. 3. 4. 5. 6. 7.
O. BAYER, Angew. Chem. 59: 257, 1947 D. J. LIMAN, J. Polymer Sci. 45: 49, 1960 M. E. BAILEY, V. KIRSS and R. G. SPAUNBURGH, Ind. Engng. Chem. 48: 794, 1956 V. Ye. ESKIN, Zh. tekh. fiz. 28: 1459, 1958 A. Ye. NESTEROV and Yu. S. LIPATOV, Vysokomol. soyed. BP: 695, 1967 W. H. STOCKMAYER and M. FIXMAN, J. Polymer Sci. C1: 137, 1963 V. Ye. ESKIN, Uspekhi fiz. nauk 82: 649, 1964
THE COMPOSITIONAL AND MOLECULAR WEIGHT INHOMOGENEITY OF N-VINYLPYRROL1DONE-VINYL ACETATE COPOLYMERS* V. A. AGASAIWDYAI~, L. G. KUDRYAVTSEVA, A. D. LITI~IAIWOWICH and V. VA. SHTERI~ A. V. Topchiev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences (Received 7 December 1966)
COPOLYMERS of N-vinylpyrrolidone (VP) with vinyl acetate (VA) can be used as starting materials for the preparation of medical products based on copolymers, i.e. for the production of blood substitutes [1]. For the preparation of such products it is very essential that the original copolymer should be sufficiently uniform in both composition and molecular weight. The most general method for preparation of copolymers of uniform composition is by synthesis in a continuous flow reactor with adequate stirring [2]. A copolymer prepared under these conditions should also have a narrower molecular weight distribution than copolymers prepared under static conditions [3]. * Vysokomol. soyed. AP: No. 12. 2634-2636, 1967.
2980
V . A . AGASANDYA3~Teg o~.
I n this w o r k the compositional a n d molecular weight i n h o m o g e n e i t y o f t w o samples of V P - V A copolymers were compared, one o f which was p r e p a r e d in a c o n t i n u o u s r e a c t o r a n d the o t h e r u n d e r static conditions. The t w o samples were p r e p a r e d a t fairly high a n d almost identical degrees of conversion a n d t h e average mole fractions o f V P in t h e c o p o l y m e r (~) a n d the intrinsic viscosities ([~/]) were v e r y similar.
EXPERIMENTAL The batch-process copo]yiner was prepared in solution in isopropanol in an atmosphere of nitrogen at 70° with polymerization time of 1'5 hr. The concentration of the monomer mixture in the solution was ~ 24~o by volume, the molar composition of the initial monomer mixture was VP:VA=0"32:0"68 and the initial concentration of azobisisobutyronitrile was 10-z mole/1, of monomer mixture. The conditions of preparation in the continuous reactor and the methods of purification of the reagents and isolation of the copolymers were described in reference [4]. The average characteristics of the eopolymers were: a) in the continuous reactor, conversion 69"5% by weight ,[~/]=0"11 cU/g, ==0"53; b) under static conditions, conversion 68"2~o by weight, [~/]----0"12 dl/g, ==0"525.
7~
0"5
i
1
i
o~
I
l'O
FIG. 1. Dependence of the precipitation threshold (~*) on copolymer composition (=) for the systems: 1--dJethyl ether-~cetone, 2--n-hexane-isopropanol. For characterization of the compositional and molecular weight inhomogeneity of the copolymers we used the method of cross fractionation [5]. This method was chosen because it is more e~Rcient than successive precipitation or branched fractionation [6, 7]. The most efficient preclpitant-solvent system for cross fraetionation was chosen on the basis of a study of the dependence of the precipitation threshold y* (the volume fraction of the precipitant in the solution at the moment of appearance of turbidity) on the copolymer composition ~. In conformity with the requirements of the method of selection of a precipitanf~solvent system for fractionation of copolymers [8] the dependence of y* on = was studied
Weight inhomogeneity of N-vinylpyrrolidone-vinyl acetate copolymers ~EAN
2981
COMPOSITIONS (~) AND I N T R I N S I C VISCOSITIES ([11]) OF FRACTIONS OF COPOLYMERS
rR~PA~ED I~ A co~ri~vovs
Characteristic
A~D V I ~ D E R STATIC C O ~ D m O N S
m
a
b C
d
[,1]
REAC~O~ ( ~ A T O ~ ) (D~NOm~ATOR)
a
b C
d
0.530/0.515 0.555/0.630 0.555/0.650 0.535/0.625 0.150/0.200 0.135/0.200 0.130/0.155 0.110/0.125
0-530/0'430 0.530/0"480 0.530/0"515 0"545/0"590 0"125/0"120 0"115/0"110 0.110/0.105
0.085/0.090
0.510/0'335 0.530/0.410 0.530/0.465 0.520/0.505 0"090/0"080 O.O9O/O"O75 0.085/0.075 O'O7O/O'O5O
with copolymers of fairly high molecular weight (10 s) a n d uniformity of composition prepared b y copolymerization to a conversion of 2 - 3 % . F r o m the results of preliminary experiments we selected the systems diethyl e t h e r acetone and n-hexane-isopropanol for the fractionation. I t is seen from Fig. 1 t h a t in the region of ~~ 0.5, in which we are interested, in the first system 7* falls fairly r a p i d l y a n d in the second system rises with increase in ~. This pair of systems therefore satisfy the requirements of the cross fractionation method. The copolymers were first separated into three fractions in the ether-acetone system, then each of these fractions was further fractionated in the n-hexane-isopropanol system. Fractionation was carried out at 24 ° in accordance with the generally adopted m e t h o d [9]. All the fractions were reprecipitated from solution in isopropanol b y ether and the precipitates were dissolved in water a n d freeze-dried. The intrinsic viscosity (It/I) was determined in water a t 25 °. The composition of t h e fractions was determined with t h e a i d of an I T R - 2 interferometer. All the measurements were m a d e in solution in methanol at a concentration of 0"01 g/cm 8 a t 20 °. The difference between the refractive indices (R) in solutions of VP and VA homopolymers is zfR= 7"4 × 10 -~. The copolymer composition was determined from the value of R, assuming a linear relationship between the composition of the copolymer a n d refractive index. The relative error in determination of the composition of the fractions was 4-3~o. D a t a on the composition and intrinsic viscosity of the fractions are given in t h e Table (where n = 1-3 are the code numbers of the initial fractions and m - - a - d the numbers of t h e final fractions). RESULTS AND DISCUSSION
Curves of the integral composition distribution (I~) of the copolymers prepared in the continuous reactor and by the batch process were constructed from the data in the Table (Fig. 2). The I~ curves were constructed on the basis of the usual assumption that overlapping of the differential composition distribution curves for the fractions is small [6]. For estimation of the molecular weight inhomogeneity of the copolymers we used the integral (I[~]) and differential (W[~]) intrinsic viscosity distribution
V. A. AGASANDYANe~ a~.
2982
curves, because there are no data available on the relationship between [t/] and molecular weight for V P - V A copolymers. The I[,] and WE,1 curves were constructed b y the method of Tung [10] (Fig. 3).
11 0
1"01
011
03
~
i
Oq
I
05
0.6
I
O~7cz
O~l
FIG. 2
0"2
[~]
Fm. 3
Fro. 2. Integral composition distribution curves for VP-VA copolymers prepared in a continuous reactor (1) and under static conditions (2). Fzo. 3. Integral (I[~]) and differential (W[~])intrinsic viscosity distribution curves for VP-VA copolymers prepared in a continuous reactor (1, 1") and under static conditions (2, 2'). I t is seen from Figs. 2 and 3 that the copolymer prepared in the continuous reactor is considerably more homogenous with respect to composition and molecular weight than the sample prepared b y the batch method. CONCLUSIONS
A study has been made of samples of a copolymer of N-vinylpyrrolidone and vinyl acetate prepared in a continuous reactor with ideal mixing and under static conditions to a degree of conversion of 70% b y weight, and having the same average characteristics (intrinsic viscosity and composition). I t is shown b y means of cross fractionation that the sample prepared in the continuous reactor is considerably more homogenous with respect to composition and molecular weight than the sample prepared under static conditions. Trana/ate~ by E. O. pwrrm~ps REFERENCES
1. S. N. USHAKOV, Sinteticheskie polimery lekarstvennogo naznacheniya (Synthetic Polymers for Medical Purposes). Medgiz, 1962 2. F. T. WALL, C. J. DELBECK and R. E. FLORIN, J. Polymer Sei. 9: 177, 1952
]:)epolymerization of polypropylene during inhibited oxidation
2983
3. K. G. DENBIGH, Trans. F a r a d a y Soc. 43: 648, 1947 4. V. A. AGASANDYAN, A. D. L1TMANOVICH a n d V. Ya. SHTERN, K i n e t i k a i kataliz 8: 773, 1967 5. A. I. ROSENTHAL a n d B. B. WHITE, I n d Engng. Chem. 44: 2693, 1952 6. A. D. LITMANOVICH and V. Y a . SHTERN, International Symposium on Macromolecular Chemistry, P r e p r i n t 130, Prague, 1965 7. L. G. KUDRYAVTSEVA and A. I). LITMANOVICH, Vysokomol. soyed. A9: 18, 1967 8. A. D. LITMANOVICH, Dissertation, 1963 9. P. W. ALLEN, Metody issledovaniya polimerov (Techniques of Polymer Characterization). Foreign Literature Publishing House, 1961 (Russian translation) I0. L. H. TUNG, J. Polymer Sci. 29: 495, 1956
INVESTIGATION OF THE DEPOLYMERIZATION OF POLYPROPYLENE DURING THE COURSE OF INHIBITED OXIDATION* B. A. GROMOV and Yu. A. SHLYAPNIKOV Chemical Physics Institute, U.S.S.R. A c a d e m y of Sciences.
(Received 10 December 1966)
h ' HAS been shown [1] that, during the induction period in the inhibited oxidation of polyolefins, changing quantities of low molecular olefins are formed; these are the products of the depolymerization of aliphatic maeroradicals. Thus the rate of formation of a specific olefin should be proportional to the concentration of macroradicals with a certain structure with a free valency at the end of the polymer chain, and m a y serve as a measure of the concentration of such radicals. Clearly, the break-away of hydrogen atoms from a sufficiently large macromolecule, taking place according to "the law of chance", will lead predominantly to the formation of macro-radicals with the free valency in the middle of the polymer chain, and therefore, in studying the formation of olefins, one should watch out for radicals with a "secondary" mode of origin. EXPERIMENTAL Isotactic polypropylene with an intrinsic viscosity of [~/]=3"1 (tetralin, 135 °C), purified as described in reference [2], was used in this work. The inhibitors, namely, 2,4,6-tritert.butylphenol, melting point 132 °C a n d 2,2'-methylene-bis-(4-methyl-6-tert.butylphenol), melting point 126 °C, were purified b y distillation in vacuum. The specimens of polypropylene containing the inhibitor were heated in sealed ampoules in an oxygen atmosphere for a given time; after being cooled, the gases contained in the ampoule were expelled b y water into a syringe and then introduced into the chromatograph (silica-gel; 90 cm; 60°C; carrier gas-hydrogen, 20 ml/min; flame-ionization detector). * Vysokomol. soyed. Ag: No. 12, 2637-2640, 1967.