Viscometric investigations on the intrinsic viscosity of polyvinylpyrrolidone affected by polymer-polymer interactions in solution

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1 e-polymers 2003, no ISSN Short communication: Viscometric investigations on the intrinsic viscosity of polyvinylpyrrolidone affected by polymer-polymer interactions in solution Omar Melad AL-Azhar University, Department of Chemistry, P.O. Box 1277, Gaza, Palestine; (Received: March 13, 2003; published: May 6, 2003) Abstract: The intrinsic viscosity of polyvinylpyrrolidone (PVP) and various added polymers was investigated by the polymer-solvent method. It has been found that both polymer-polymer interactions and the concentration of the added polymer affect the intrinsic viscosity of PVP. In the polymer-solvent system poly(methyl methacrylate) + dimethylformamide (PMMA+DMF), the intrinsic viscosity of PVP decreases as the concentration of PMMA increases, showing that the repulsive interaction between PVP and PMMA originates from the contraction of PVP coils in solution due to the intermolecular excluded volume. However, in the polymersolvent systems poly(vinyl chloride) (PVC) + DMF or poly(vinylidene fluoride) (PVDF) + DMF, the attractive interactions between PVP and PVC or PVDF cause an expansion of PVP coils in solution at high concentrations of PVC or PVDF. The polymer-solvent method allows estimating the compatibility of the used polymers. Introduction The polymer-solvent method, which has received much attention in recent years [1-5], has proved to be a useful technique to investigate polymer-polymer interactions in solution. In this method, the viscosity behaviour of polymer A (guest polymer), is determined in a solution that contains a second polymer B (host polymer) at constant concentration [3,5]. It is often believed that in solution the polymer-polymer interaction dominates over polymer-solvent interaction [6,7]. The polymer-solvent interaction uses to be associated with features such as the polarity or the dielectric constant of the solvent [1]. Polymer-polymer compatibility has been extensively studied by several techniques [1]. Dilute-solution viscometry (DSV) is the best technique to study polymer-polymer interactions [8-15]. In this investigation, the intermolecular interaction between PVP and various polymers such as poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA) and poly(vinylidine fluoride) (PVDF) was determined by the polymer-solvent method, PVP being the guest and the others the host polymers. The experimental results of the viscosity measurements provide much information about polymer-polymer interactions and the compatibility of the different polymers through the sign of [η A ] B. 1

2 Experimental part PVP, PVC, PMMA and PVDF with average molecular weights of , , and , respectively, were supplied by Aldrich (USA). All polymers were used as received without further purification. Dimethylformamide (DMF) was purchased from chemical laboratory Riedel-de Haen (Germany) and was used as solvent. The guest polymer (PVP) was dissolved in different concentrations ranging from 0.13 to 1.1 g/dl. Viscometric measurements were carried out using a Cannon-Fenske-type capillary viscometer equipped with a model OSK 2876 that was immersed in a constant temperature bath. The temperature was 26.0 ± 0.1 C measured by a thermometer with an accuracy of 0.01 C. The uncertainty in the observed measurements was estimated to be less than 5% for all the systems. Results and discussion In the framework of the formalism developed by Krigbaum-Wall [16] and Cragg- Bigelow [17], the reduced viscosity of a polymer in solution follows the linear relationship given by the Huggins equation: η sp /c = [η] + b c (1) where b = K H [η] 2 and [η] = lim c 0 (η sp /c). Here, (η sp ), [η], c, b and K H denote the specific viscosity, the intrinsic viscosity, the polymer concentration, the viscometric interaction parameter and the Huggins constant, respectively. Measurements of the reduced viscosities of the polymers have been conducted and their respective plots fitted with Eq. (1). Fig.1a shows the plots of reduced viscosity (η sp /c) vs. concentration for PVP in the pure solvent DMF and in the polymer-solvent PMMA+DMF at 26 C. The plots are linear. On extrapolating to zero concentration, both intrinsic viscosity [η] and viscometric interaction parameter, b, can be obtained. Their values are tabulated in Tab. 1. The decrease of the intrinsic viscosity of PVP in PMMA+DMF can be attributed to the repulsive intermolecular interaction between PVP and PMMA in solution. Tewari and Srivastava [1] pointed out that the most important polymer-polymer interaction is the thermodynamic interaction that includes the intramolecular excluded volume effect, resulting in an expansion of the coil in solution, and the intermolecular excluded volume effect, resulting in a contraction of the coil. The repulsive intermolecular interaction between PVP and PMMA in solution will increase the intermolecular excluded volume effect. As a result, the PVP coils shrunk in size and the intrinsic viscosity of PVP decreases in the polymer-solvent PMMA+DMF. Fig. 2a shows that the intrinsic viscosity of PVP in the polymer-solvent PMMA+DMF decreases as the concentration of PMMA in the polymer-solvent PMMA+DMF increases. At higher concentration of PMMA (c PMMA = 1.08 g/dl), the intrinsic viscosity slightly increases as can also be seen in Tab. 2. The interpretation could be that the intermolecular excluded volume effect is also concentration dependent. Fig.1b shows the plots of reduced viscosity (η sp /c) vs. concentration for PVP in DMF and in PVC+DMF at 26 C. It can be seen that the intrinsic viscosity of PVP in the polymer-solvent PVC+DMF is higher than in the case of the pure solvent DMF. The considerable increase in the intrinsic viscosity of PVP in PVC+DMF is due to the strong hydrogen-bond-type interaction between PVP and PVC. This attractive interaction decreases the intermolecular excluded 2

3 volume effect. Therefore, the intrinsic viscosity of PVP in the polymer-solvent PVC+DMF increases because PVP coils are expanded due to the intramolecular excluded volume effect. Fig. 1. Plots of the reduced viscosity η sp /c vs. concentration for PVP in DMF and in (a) DMF+PMMA, c PMMA = 1.08 g/dl, (b) DMF+PVC, c PVC = g/dl, and (c) DMF+PVDF, c PVDF = g/dl at 26 C 3

4 Tab. 1. Viscosity data for PVP in pure solvent DMF and in polymer-solvent systems at 26 C System [η] b in (dl/g) 2 PVP in DMF PVP in DMF+PMMA PVP in DMF+PVC PVP in DMF+PVDF Fig. 2. Plots of the intrinsic viscosity () of PVP in (a) DMF+PMMA vs. conc. of PMMA, (b) DMF+PVC vs. conc. of PVC, and (c) DMF+PVDF vs. conc. of PVDF at 26 C 4

5 Tab. 2. Intrinsic viscosity of PVP in differently concentrated polymer-solvent systems at 26 C c PMMA [η PVP ] PMMA [η PVP ] PMMA c PVC [η PVP ] PVC [η PVP ] PVC c PVDF [η PVP ] PVDF [η PVP ] PVDF in g/dl in g/dl in g/dl Fig. 2b shows that, at lower concentration (c PVC 1.08 g/dl), the intrinsic viscosity of PVP in the polymer-solvent PVC+DMF will decrease in the further concentrated polymer-solvent as seen also in Tab. 2. This is the correct behaviour because in the concentrated polymer-solvent PVC+DMF, the attractive interaction between PVP and PVC should become stronger, and hence the intrinsic viscosity of PVP, [η PVP ] PVC, should increase in the highly concentrated polymer-solvent PVC+DMF. Fig. 1c shows the reduced viscosity η sp /c vs. concentration for PVP in DMF and in PVDF+DMF at 26 C. It can be observed that the value of the intrinsic viscosity of PVP in the polymer-solvent PVDF+DMF is higher than in DMF. This behaviour can be attributed to the strong attraction between PVP and PVDF in solution. It can be seen in Fig. 2c that the intrinsic viscosity of PVP in the polymer-solvent PVDF+DMF decreases as the concentration of polymer-solvent increases, reaching a minimum value, and then sharply increases at c = 0.75 g/dl. From this value a slight decrease with polymersolvent concentration is observed. The interpretation is similar to that of the experimental results of PVP in the polymer-solvent PVC+DMF. Taking into account the significant improvement in material properties that can be achieved in polymer blends over their individual components, it is not surprising that extensive efforts have been made in order to study the miscibility of polymers [1,18-20]. These studies have been performed not only in industry but also in several academic laboratories, with the aim of improving material properties and understanding the fundamental relationships between polymer miscibility, the properties of the individual materials, and the properties of blends. The compatibility of two polymers was investigated using the compatibility criteria based on the difference between the experimental and the theoretical values of [η] and b, which are [η] and b, reported in many articles [21-23]. The criterion [η A ] B = [η A ] B - [η A ] for the polymer-solvent method was used to predict the polymerpolymer compatibility [14]: if [η A ] B 0, then polymers A and B are compatible, whereas [η A ] B 0 indicates that polymers A and B are incompatible. Tab. 2 shows that the value of [η PVP ] PMMA decreases and approaches to zero at c = 0.40 g/dl; then it becomes negative in the concentrated polymer-solvent PMMA+DMF, [η PVP ] PMMA < 0, indicating that PVP and PMMA are incompatible polymers, while the values of [η PVP ] PVC and [η PVP ] PVDF > 0 in all concentrated polymersolvent systems PVC+DMF and PVDF+DMF, respectively, indicating that PVP and PVC as well as PVP and PVDF are compatible polymers. The degree of compatibility 5

6 between all these polymer pairs is in general as follows: PVP+PVDF PVP+PVC > PVP+PMMA, at different concentrations of host polymers. Conclusion PVP has been used as a guest polymer and PMMA, PVC and PVDF as host polymers in DMF solutions. The viscosity behaviour of PVP in different polymersolvent systems affected by both the polymer-polymer interaction and the concentration dependent intermolecular excluded volume effect was investigated. It is noted that the interaction between PVP and PMMA is repulsive whereas those between PVP/PVC and PVP/PVDF are attractive. The criteria [η A ] B 0 for the compatible case and [η A ] B 0 for the incompatible one could be applied in this paper. [1] Olabisi, O.;Robeson, L. M.; Shaw, T.; Polymer-Polymer Miscibility, Academic Press, New York [2] Kosai, K.; Higashino, T.; Nipffpen Setchaku Kyokai Shi 1975,11, 2. [3] Ichihara, S.; Komatsu, A.; Hata, T.; Polym. J. 1971, 2, 640. [4] Peterson, R. J.; Corneliussen, R. D.; Rozelle, L. T.; Polym. Prepr. (Am. Chem. Soc. Div. Polym. Chem.) 1969, 10, 385. [5] Friese, F.; Plaste Kautsch. 1968, 15, 646. [6] Kulshreshtha, A. K.; Singh, B. P.; Sharma, Y. N.; Eur. Polym. J. 1988, 24, 191. [7] Mamza, P. A. A. P.; Folaranmi, F. M.; Eur. Polym. J. 1996, 32, 909. [8] Sun, Z. H.; Wang, W.; Feng, Z. L.; Eur. Polym. J. 1992, 28, [9] Chee, K. K.; Eur. Polym. J. 1990, 26, 423. [10] Kulshreshtha, A. K.; Singh, B. P.; Sharma, Y. N.; Eur. Polym. J. 1988, 24, 29. [11] Kulshreshtha, A. K.; Singh, B. P.; Sharma, Y. N.; Eur. Polym. J. 1988, 24, 23. [12] Montelro, E. E. C.; Thaumalurgo, C.; Polym. Bull. 1993, 30, 697. [13] Lizymol, P. P.; Thomas, S.; Eur. Polym. J. 1994, 30, [14] Danait, A.; Deshparrde, D. D. ; Eur. Polym. J. 1995, 31, [15] Zhu, P. P.; Wang, P.; Eur. Polym. J. 1997, 33, 411. [16] Krigbaum, W. R.; Wall, F. W.; J. Polym. Sci. 1950, 5, 505. [17] Cragg, L. H.; Biegelow, C. C.; J. Polym. Sci. 1955, 16, 177. [18] Polymer Blends, Paul, D. R; Newman, S; editors; Academic, New York [19] Utracki, L. A.; Polymers Alloys and Blends: Thermodynamics and Rheology, Hanser, München [20] Multiphase Polymers: Blends and Ionomers, Utracki, L. A; Weiss, R. A.; editors; ACS Symp. Ser. 395; Am. Chem. Soc., Washington, DC [21] Garcia, R; Melad, O.; Gomez, C. M.; Figueruelo, J. E.; Campos, A.; Eur. Polym. J. 1999, 35, 47. [22] Melad, O.; Asian J. Chem. 2002, 14, 849. [23] Melad, O.; Baraka, R.; Salem, J. K. J.; Hilles, H.; El-Khazendar, A.; Chinese J. Polym. Sci. 2003, 21, 15. 6