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polystyrene (PS) blends in various solvents
PERGAMON
European Polymer Journal 35 (1999) 915±921
Viscosity behavior of incompatible poly(vinyl chloride) (PVC)/polystyrene (PS) blends in various solvents Zhu Pingping *, Yang Haiyang, Zeng Yiming Dept. of Polymer Science and Engineering, University of Science and Technology of China, Anhui Hefei 230026, P.R. China Received 24 June 1997; accepted 5 December 1997
Abstract The viscosimetric measurements were carried out for poly(vinyl chloride) (PVC), polystyrene (PS) and a (50:50) blend of incompatible PVC/PS in three dierent solvents at 208C. The results showed that the choice of solvent had a great in¯uence on the viscosity behavior of incompatible blends. A detailed discussion, including about the compatible blends, was given in this article. It was concluded that, the viscosity behavior of a ternary polymer± polymer±solvent system originated from a superposition of several types of hydrodynamic and thermodynamic interactions. Specially, the nature of the solvent in¯uenced the competition among these thermodynamic interactions in solution. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction It is well known that the dilute solution viscometry is a simple and quick method for determining polymer±polymer miscibility [1±6]. Investigation of viscometry behavior of a ternary (polymer±polymer± solvent) system also gives useful information about interactions [7±10]. The principle of using a dilute solution viscosity to measure the miscibility characterization is based on the fact that, while in solution, molecules of both component polymers may exist in a molecularly dispersed state and undergo a mutual attraction or repulsion which will in¯uence the viscosity. It is assumed that polymer±polymer interactions usually dominate over polymer±solvent ones. Attraction between two component molecules may cause swell of macromolecular coils resulting in an increase in viscosity, or otherwise, repulsion may cause shrinkage of the macromolecular coils giving a decrease in viscosity. So it is
* Corresponding author.
suggested [10] that using the change in slope of reduced viscosity (Zsp/c)±concentration (c) plot as a criterion to determine polymer±polymer compatibility, schematically displayed in Fig. 1. For the incompatible blends, the incompatible molecules refuse to overlap and polymer molecules shrink in size, which leads to a decrease in hydrodynamic volumes and this causes the reduction of the reduced viscosity. The crossover in the reduced viscosity±concentration plot is observed. It is veri®ed by the ternary solution: polystyrene (PS)± poly(methyl methacrylate) (PMMA)±benzene at 308C [11]. On the contrary, for the compatible blends, mutual attraction of component molecules leads to an increase in hydrodynamic volumes, so an increase in the slope of reduced viscometry±concentration plot is observed. It is veri®ed by the ternary solution: poly-ecaprolactone (PCL)±poly(vinyl chloride) (PVC)-N,N 0 dimethyl formamide (DMF) at 258C [9, 10]. In a ternary (polymer±polymer±solvent) system, the thermodynamic interactions are the most important, beside the hydrodynamic interactions. The thermodynamic interactions include interaction between segments of the same polymer, interaction between each com-
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 8 ) 0 0 0 6 4 - 0
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Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 1. The variation of reduced viscosity with concentration is schematically shown.
ponent polymer and solvent, and interaction between two component polymers. All these interactions are the contributing factors in the change of viscosity, but differing in extent, which might depend on the nature of solvent. However, only a small amount of work has been reported on this respect [9, 12, 13]. In our previous work, we have investigated the viscosity behavior of compatible PCL/PVC blends in various solvents [9]. It was found that the attraction between PCL and PVC could cause the viscosity behavior of the solution to deviate from the viscosity additivity to such an extent, depending on the nature of solvent. Also the solvent power could be altered by varying the composition of a mixed solvent [13]. These facts imply that, for the viscosity behavior of a ternary solution, the choice of solvent is of vital importance for the study. Under certain circumstances, the above assumption that polymer±polymer interactions dominated over polymer±solvent ones, is virtually invalid. Our results dier from the work of Kulshreshtha et al. [14], who concluded that the versatility of viscosimetric techniques is not aected by the choice of solvent. The present paper, which is a continuation of our previous investigation [9, 10, 13], further reports on the results about the in¯uence of the choice of solvent on the viscosity behavior of incompatible blends: poly(vinyl chloride) (PVC)/polystyrene (PS). The PVC/PS blends have been proved to be immiscible on the basis of damping measurement [15] and viscometry [2]. In
this work, N,N 0 -dimethyl formamide (DMF), tetrahydrofuran (THF) and 1,2-dichloroethane (DCE) have been selected as solvents, respectively, because of their considerable dierence in structure.
2. Experiment Poly(vinyl chloride) (PVC) and polystyrene (PS) used in this work were kindly supplied by Hefei Chemistry Plant (China), with viscosity average molecular weight of 70000 and 250000, respectively. The relative viscosity of the polymer solutions was measured at 208C using Ubbelohde dilute viscosimeters. Each of the original binary solutions were prepared by dissolving a measured amount (wt) of polymer in solvent, and diluting to a measured volume. The ternary solutions were prepared by thoroughly mixing measured volumes of two binary solutions, the mixing being done directly in the viscosimeter.
3. Results and discussion Viscosimetry plots, obtained for each of the original binary solutions PVC±solvent and PS±solvent, are shown in Figs 2 and 3, respectively. The values of (Zsp/c)c 4 0 (intrinsic viscosity, [Z]) are cited in Table 1.
Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 2. Plots of reduced viscosity vs concentration for PVCD in three dierent solvents at 208C.
Fig. 3. Plots of reduced viscosity vs concentration for PS in three dierent solvents at 208C.
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Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Table 1 The intrinsic viscosity's of PVC and PS in three dierent solvents (dl/g)
PVC PS
THF
DMF
DCE
1.06 0.99
0.75 0.51
1.72 0.76
It has been proved [16] that the intrinsic viscosity, [Z], usually changes proportionally for a given change in solvent power, this is used as an experimental criterion of solvent power. The above results imply that tetrahydrofuran (THF) and 1,2-dichloroethane (DCE) are good solvents for both polymers (PVC and PS), But N,N-dimethyl formamide (DMF) is rather poor. Specially for the PVC±DCE solution, the reduced viscosity (Zsp/c) increases greatly with decrease in concentration (c) in the low concentration range. This fact may be ascribed to the great interaction between polymer and solvent due to similarity in the chemical struc-
ture, polarity between PVC and DCE, in concert with the adage ``like likes like'' Ð largely a combinatorial entropy driven phenomenon [9, 17]. Figs 4±6 show the Huggins plots for the (50:50) blend of PVC/PS in these solvents. In Fig. 4, a crossover is observed and a decrease of slope occurs in about 0.72 g/100 ml in the viscosity±concentration plot of PVC±PS±THF solution. The crossover occurs at a concentration which is related to the molecular weights of the constituent homopolymer [11, 18]. Above this concentration, two incompatible polymers, PVC and PS, undergo a mutual repulsion in dilute solution, the hydrodynamic volume of chains is lower. The reduction of hydrodynamic volume will result in a decrease in the reduced viscosity of solution, correspondingly, the slope of the plot of reduced viscosity against concentration may suddenly decline. Dondos et al. [11] also observed the similar crossover for the incompatible blend polystyrene±poly(methyl methacrylate) in benzene.
Fig. 4. Plots of reduced viscosity vs concentration for PVC, PS and a (50:50) blend in THF at 20 8C.
Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 5 shows the viscosity±concentration plots for PVC, PS and the blend PVC/PS (50:50) in DMF, which are all linear. No crossover is observed in the plot for this ternary system (PVC±PS±DMF). This fact is dierent from these reported earlier [11, 18]. So it can be seen that the appearance of crossover depends upon the solvent. As is well known [19, 20], in a good solvent, the favorable interaction between polymer and solvent corresponding to the repulsive interaction between segments of a polymer chain, causes the macromolecule to expand, for example, PVC in THF, PS in THF. But in ternary PVC±PS±THF solution, as concentration increases, the unlike polymer chains do not tend to overlap and therefore shrink in their size because of the incompatibility of two polymers. On the other hand, in a poor solvent, as the polymer±solvent interaction is unfavorable, segments of a polymer chain are attracted, this leads to a shrinkage of a single polymer coil. For example, PVC in DMF and PS in DMF. Relatively, the in¯uence of repulsion between PVC and PS upon the originally shrinking chains is rather weak.
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So the reduction of their hydrodynamic volume by mutual repulsion may be negligible. The viscosity behavior of the PVC/PS blend (50:50) in DCE is special, as is just shown in Fig. 6. No marked dierence between the plot of the blend and that of PVC was observed. This fact indicates that, the weak repulsion between PVC and PS seldom has an in¯uence on the great interaction between PVC and DCE. But in PCL±PVC±DCE solution [9], the attraction between PCL and PVC, reduces the interaction between PVC and DCE greatly. From this work concerning the viscosity behavior of incompatible PVC/PS blend and previous work about compatible PCL/PVC blend in various solvents [9, 13], it can be concluded that in a ternary polymer±polymer±solvent system, polymer±polymer interactions may be varied by changing a second polymer (compatible and incompatible), polymer±solvent interactions may be varied by changing the type of solvent or gradually changing the composition of a mixed solvent. The viscosity behavior of the ternary system originates from a superposition of several types of
Fig. 5. Plots of reduced viscosity vs concentration for PVC, PS and a (50:50) blend in DMF at 208C.
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Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 6. Plots of reduced viscosity vs concentration for PVC, PS and a (50:50) blend in DCE at 208C.
interactions, the hydrodynamic and thermodynamic interactions being the most important. The intramolecular excluded volume eect, which includes the segment repulsion of a polymer in a good solvent and the intermolecular attraction of compatible blends, result in an expansion of the coil. The intermolecular excluded volume eect, including the segment attraction of a polymer in a poor solvent and the intermolecular repulsion of incompatible blends, results in contraction of the coil. The competition among these interactions depend upon the power of solvent. Hence the viscosity method has been proven to be a simple and eective tool for investigating the interactions in dilute solution of polymer blend.
References [1] Chee KK. Eur Polym J 1990;26:423. [2] Danait A, Dashpande DD. Eur Polym J 1995;31:1221. [3] Kulshreshtha AK, Singh BP, Sharm YN. Eur Polym J 1988;24:29. [4] Kulshreshtha AK, Singh BP, Sharma YN. Eur Polym J 1988;24:33. [5] Zhu PW. Eur Polym J 1995;31:659. [6] Zhu PP. Eur Polym J 1997;33(3):411. [7] Lizymol PP, Thomas S. Eur Polym J 1994;30:1135. [8] Williamson GR, Wright B3:3885. [9] Zhu PP, Yang HY, Wang SQ. Eur Polym J 1998;34(1):91.
Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921 [10] Yang HY, Zhu PP, Wang SQ, Guo QP. Eur Polym J 1998;34(3±4):463. [11] Dondos A, Skondrs P, Pierri E, Benoit H. Makromol Chem 1983;184:2153. [12] Tewari N, Srivastava AK. Macromoleculars 1992;25(3):1013. [13] Yang HY, Zhu PP, Wang SQ, Zeng YM, Guo QP. Eur Polym J 1998;34(9):1303. [14] Qian RY, Singh BP, Sharma YN. Eur Polym J 1988;24:191.
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[15] Buchdahl R, Nielsen LE. J Polym Sci 1955;5:11. [16] Cragg LH, Bigelow CC. J Polym Sci 1955;16:177. [17] Bhagwagar DE, Serman CJ, Painter PC, Coleman MM. Macromolecules 1989;12:4656. [18] Pierri E, Dondos A. Eur Polym J 1987;23:347. [19] Flory PJ. Principle of Polymer Chemistry. New York: Cornell University Press, 1953. [20] Qian RY. The Molecular Weight Measurement of Polymer. Beijing: Science Press, 1958.
European Polymer Journal 35 (1999) 915±921
Viscosity behavior of incompatible poly(vinyl chloride) (PVC)/polystyrene (PS) blends in various solvents Zhu Pingping *, Yang Haiyang, Zeng Yiming Dept. of Polymer Science and Engineering, University of Science and Technology of China, Anhui Hefei 230026, P.R. China Received 24 June 1997; accepted 5 December 1997
Abstract The viscosimetric measurements were carried out for poly(vinyl chloride) (PVC), polystyrene (PS) and a (50:50) blend of incompatible PVC/PS in three dierent solvents at 208C. The results showed that the choice of solvent had a great in¯uence on the viscosity behavior of incompatible blends. A detailed discussion, including about the compatible blends, was given in this article. It was concluded that, the viscosity behavior of a ternary polymer± polymer±solvent system originated from a superposition of several types of hydrodynamic and thermodynamic interactions. Specially, the nature of the solvent in¯uenced the competition among these thermodynamic interactions in solution. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction It is well known that the dilute solution viscometry is a simple and quick method for determining polymer±polymer miscibility [1±6]. Investigation of viscometry behavior of a ternary (polymer±polymer± solvent) system also gives useful information about interactions [7±10]. The principle of using a dilute solution viscosity to measure the miscibility characterization is based on the fact that, while in solution, molecules of both component polymers may exist in a molecularly dispersed state and undergo a mutual attraction or repulsion which will in¯uence the viscosity. It is assumed that polymer±polymer interactions usually dominate over polymer±solvent ones. Attraction between two component molecules may cause swell of macromolecular coils resulting in an increase in viscosity, or otherwise, repulsion may cause shrinkage of the macromolecular coils giving a decrease in viscosity. So it is
* Corresponding author.
suggested [10] that using the change in slope of reduced viscosity (Zsp/c)±concentration (c) plot as a criterion to determine polymer±polymer compatibility, schematically displayed in Fig. 1. For the incompatible blends, the incompatible molecules refuse to overlap and polymer molecules shrink in size, which leads to a decrease in hydrodynamic volumes and this causes the reduction of the reduced viscosity. The crossover in the reduced viscosity±concentration plot is observed. It is veri®ed by the ternary solution: polystyrene (PS)± poly(methyl methacrylate) (PMMA)±benzene at 308C [11]. On the contrary, for the compatible blends, mutual attraction of component molecules leads to an increase in hydrodynamic volumes, so an increase in the slope of reduced viscometry±concentration plot is observed. It is veri®ed by the ternary solution: poly-ecaprolactone (PCL)±poly(vinyl chloride) (PVC)-N,N 0 dimethyl formamide (DMF) at 258C [9, 10]. In a ternary (polymer±polymer±solvent) system, the thermodynamic interactions are the most important, beside the hydrodynamic interactions. The thermodynamic interactions include interaction between segments of the same polymer, interaction between each com-
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 8 ) 0 0 0 6 4 - 0
916
Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 1. The variation of reduced viscosity with concentration is schematically shown.
ponent polymer and solvent, and interaction between two component polymers. All these interactions are the contributing factors in the change of viscosity, but differing in extent, which might depend on the nature of solvent. However, only a small amount of work has been reported on this respect [9, 12, 13]. In our previous work, we have investigated the viscosity behavior of compatible PCL/PVC blends in various solvents [9]. It was found that the attraction between PCL and PVC could cause the viscosity behavior of the solution to deviate from the viscosity additivity to such an extent, depending on the nature of solvent. Also the solvent power could be altered by varying the composition of a mixed solvent [13]. These facts imply that, for the viscosity behavior of a ternary solution, the choice of solvent is of vital importance for the study. Under certain circumstances, the above assumption that polymer±polymer interactions dominated over polymer±solvent ones, is virtually invalid. Our results dier from the work of Kulshreshtha et al. [14], who concluded that the versatility of viscosimetric techniques is not aected by the choice of solvent. The present paper, which is a continuation of our previous investigation [9, 10, 13], further reports on the results about the in¯uence of the choice of solvent on the viscosity behavior of incompatible blends: poly(vinyl chloride) (PVC)/polystyrene (PS). The PVC/PS blends have been proved to be immiscible on the basis of damping measurement [15] and viscometry [2]. In
this work, N,N 0 -dimethyl formamide (DMF), tetrahydrofuran (THF) and 1,2-dichloroethane (DCE) have been selected as solvents, respectively, because of their considerable dierence in structure.
2. Experiment Poly(vinyl chloride) (PVC) and polystyrene (PS) used in this work were kindly supplied by Hefei Chemistry Plant (China), with viscosity average molecular weight of 70000 and 250000, respectively. The relative viscosity of the polymer solutions was measured at 208C using Ubbelohde dilute viscosimeters. Each of the original binary solutions were prepared by dissolving a measured amount (wt) of polymer in solvent, and diluting to a measured volume. The ternary solutions were prepared by thoroughly mixing measured volumes of two binary solutions, the mixing being done directly in the viscosimeter.
3. Results and discussion Viscosimetry plots, obtained for each of the original binary solutions PVC±solvent and PS±solvent, are shown in Figs 2 and 3, respectively. The values of (Zsp/c)c 4 0 (intrinsic viscosity, [Z]) are cited in Table 1.
Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 2. Plots of reduced viscosity vs concentration for PVCD in three dierent solvents at 208C.
Fig. 3. Plots of reduced viscosity vs concentration for PS in three dierent solvents at 208C.
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Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Table 1 The intrinsic viscosity's of PVC and PS in three dierent solvents (dl/g)
PVC PS
THF
DMF
DCE
1.06 0.99
0.75 0.51
1.72 0.76
It has been proved [16] that the intrinsic viscosity, [Z], usually changes proportionally for a given change in solvent power, this is used as an experimental criterion of solvent power. The above results imply that tetrahydrofuran (THF) and 1,2-dichloroethane (DCE) are good solvents for both polymers (PVC and PS), But N,N-dimethyl formamide (DMF) is rather poor. Specially for the PVC±DCE solution, the reduced viscosity (Zsp/c) increases greatly with decrease in concentration (c) in the low concentration range. This fact may be ascribed to the great interaction between polymer and solvent due to similarity in the chemical struc-
ture, polarity between PVC and DCE, in concert with the adage ``like likes like'' Ð largely a combinatorial entropy driven phenomenon [9, 17]. Figs 4±6 show the Huggins plots for the (50:50) blend of PVC/PS in these solvents. In Fig. 4, a crossover is observed and a decrease of slope occurs in about 0.72 g/100 ml in the viscosity±concentration plot of PVC±PS±THF solution. The crossover occurs at a concentration which is related to the molecular weights of the constituent homopolymer [11, 18]. Above this concentration, two incompatible polymers, PVC and PS, undergo a mutual repulsion in dilute solution, the hydrodynamic volume of chains is lower. The reduction of hydrodynamic volume will result in a decrease in the reduced viscosity of solution, correspondingly, the slope of the plot of reduced viscosity against concentration may suddenly decline. Dondos et al. [11] also observed the similar crossover for the incompatible blend polystyrene±poly(methyl methacrylate) in benzene.
Fig. 4. Plots of reduced viscosity vs concentration for PVC, PS and a (50:50) blend in THF at 20 8C.
Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 5 shows the viscosity±concentration plots for PVC, PS and the blend PVC/PS (50:50) in DMF, which are all linear. No crossover is observed in the plot for this ternary system (PVC±PS±DMF). This fact is dierent from these reported earlier [11, 18]. So it can be seen that the appearance of crossover depends upon the solvent. As is well known [19, 20], in a good solvent, the favorable interaction between polymer and solvent corresponding to the repulsive interaction between segments of a polymer chain, causes the macromolecule to expand, for example, PVC in THF, PS in THF. But in ternary PVC±PS±THF solution, as concentration increases, the unlike polymer chains do not tend to overlap and therefore shrink in their size because of the incompatibility of two polymers. On the other hand, in a poor solvent, as the polymer±solvent interaction is unfavorable, segments of a polymer chain are attracted, this leads to a shrinkage of a single polymer coil. For example, PVC in DMF and PS in DMF. Relatively, the in¯uence of repulsion between PVC and PS upon the originally shrinking chains is rather weak.
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So the reduction of their hydrodynamic volume by mutual repulsion may be negligible. The viscosity behavior of the PVC/PS blend (50:50) in DCE is special, as is just shown in Fig. 6. No marked dierence between the plot of the blend and that of PVC was observed. This fact indicates that, the weak repulsion between PVC and PS seldom has an in¯uence on the great interaction between PVC and DCE. But in PCL±PVC±DCE solution [9], the attraction between PCL and PVC, reduces the interaction between PVC and DCE greatly. From this work concerning the viscosity behavior of incompatible PVC/PS blend and previous work about compatible PCL/PVC blend in various solvents [9, 13], it can be concluded that in a ternary polymer±polymer±solvent system, polymer±polymer interactions may be varied by changing a second polymer (compatible and incompatible), polymer±solvent interactions may be varied by changing the type of solvent or gradually changing the composition of a mixed solvent. The viscosity behavior of the ternary system originates from a superposition of several types of
Fig. 5. Plots of reduced viscosity vs concentration for PVC, PS and a (50:50) blend in DMF at 208C.
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Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921
Fig. 6. Plots of reduced viscosity vs concentration for PVC, PS and a (50:50) blend in DCE at 208C.
interactions, the hydrodynamic and thermodynamic interactions being the most important. The intramolecular excluded volume eect, which includes the segment repulsion of a polymer in a good solvent and the intermolecular attraction of compatible blends, result in an expansion of the coil. The intermolecular excluded volume eect, including the segment attraction of a polymer in a poor solvent and the intermolecular repulsion of incompatible blends, results in contraction of the coil. The competition among these interactions depend upon the power of solvent. Hence the viscosity method has been proven to be a simple and eective tool for investigating the interactions in dilute solution of polymer blend.
References [1] Chee KK. Eur Polym J 1990;26:423. [2] Danait A, Dashpande DD. Eur Polym J 1995;31:1221. [3] Kulshreshtha AK, Singh BP, Sharm YN. Eur Polym J 1988;24:29. [4] Kulshreshtha AK, Singh BP, Sharma YN. Eur Polym J 1988;24:33. [5] Zhu PW. Eur Polym J 1995;31:659. [6] Zhu PP. Eur Polym J 1997;33(3):411. [7] Lizymol PP, Thomas S. Eur Polym J 1994;30:1135. [8] Williamson GR, Wright B3:3885. [9] Zhu PP, Yang HY, Wang SQ. Eur Polym J 1998;34(1):91.
Zhu Pingping et al. / European Polymer Journal 35 (1999) 915±921 [10] Yang HY, Zhu PP, Wang SQ, Guo QP. Eur Polym J 1998;34(3±4):463. [11] Dondos A, Skondrs P, Pierri E, Benoit H. Makromol Chem 1983;184:2153. [12] Tewari N, Srivastava AK. Macromoleculars 1992;25(3):1013. [13] Yang HY, Zhu PP, Wang SQ, Zeng YM, Guo QP. Eur Polym J 1998;34(9):1303. [14] Qian RY, Singh BP, Sharma YN. Eur Polym J 1988;24:191.
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[15] Buchdahl R, Nielsen LE. J Polym Sci 1955;5:11. [16] Cragg LH, Bigelow CC. J Polym Sci 1955;16:177. [17] Bhagwagar DE, Serman CJ, Painter PC, Coleman MM. Macromolecules 1989;12:4656. [18] Pierri E, Dondos A. Eur Polym J 1987;23:347. [19] Flory PJ. Principle of Polymer Chemistry. New York: Cornell University Press, 1953. [20] Qian RY. The Molecular Weight Measurement of Polymer. Beijing: Science Press, 1958.