ABSTRACT:The melting temperatures of gels that were formed from dilute solutions of poly(vinyl chloride) in anisole, dioxane, and ethylene dichloride were measured over a volume fraction range from 0.02 to 0.05. Five fractions of poly(vinyl chloride) with molecular w.iights ranging from 67000 and 200000 having almost identical syndiotacticity a=0.5, were used. The linear relationship was found for each solvent between the reciprocal absolute temperature of melting and the logarithm of v2x, where V2 is the volume fraction of the polymer and x is its degree of polymerization. The X-ray diffraction pattern revealed that the gel was crystalline, thus confirming the supposition that the "cross links" are crystallites. The results were compared with the theory of melting point depression for copolymer-diluent systems. However, the theory did not fit the experimental results and it was concluded that the melting point of gel does not correspond to the thermodynamic singurality. An expression was derived from the condition of gel formation and the free energy of crystallite formation, with the supposition that the "cross links" are crystallites. The expression was compared with the experimental results, and it was found that it fairly well represents the experimentally observed gel melting points as a function of molecular weight, polymer concentration and the thermodynamic nature of the solvent. The syndiotactic sequence length in the crystallite was estimated to be 10-12.KEY WORDS Gel / Melting Temperature of Gel / Poly(vinyl chloride) / Thermally Reversible Gel / Several years ago, we observed that dilue solutions of poly(vinyl chloride) in ethyl acetoacetate are turned into gel on cooling and the gelation is reversible on warming. 1 However, the gelation phenomena is not confined the above polymer-solvent pair. Walter 2 studied the poly(vinyl chloride)-dioctyl-phthalate gel. The systems of poly(vinyl chloride)-anisole, dioxane, 3 and ethylene dichloride which we wish to report herein also exhibit thermally reversible gelation. Very recently, Harrison, Morgan, and Park 3 have reported the melting temperature of poly(vinyl chloride)-dioxan gel. Reversible gelation is by no means a unique property of poly(vinyl chloride), for this behavior has been observed for several polymer-diluent systems. 4 The well-known examples are the systems of gelatin-water and agar-water. mer chain are needed to form a three dimensional network. Taking into account this requirement for gel formation, and by treating the cross-link formation as a chemical equilibrium, Eldridge and Ferry6 derived a useful expression concerning the melting point of gel Tm g and polymer concentration C It is well known 5 from simple geometrical considerations that at least two cross-links per poly-Here C is expressed in g// and ,:JHm is the energy associated with the dissociation of a network in gel. Although many papers on gelation phenomena have appeared in the past two decades, the thermodynamics and kinetics of this sol-gel transition are not completely exp...

Simultaneous measurements of the activity coefficients of counter‐ and by‐ions in polyelectrolyte solutions were carried out. Sodium polyvinyl alcohol sulfate was used as the sample of polyelectrolyte and sodium chloride as the extraneous salt. The activity coefficient of sodium counter‐ion was determined by using a sodium amalgam electrode and that of chloride ion was determined by a sliver‐silver chloride elctrode. It was found that the activity coefficient of both counter‐ and by‐ions has little relationship with the volume of polymer coil, and that the additivity of counter‐ion activity found for hydrogen ion by Mock and Marshall holds also for sodium ion. It was also found that there is good agreement between the experimental results and the theory of Katchalsky and Lifson if we use their same theory for calculating the volume of polymer coil, although the volume is too large to be considered reasonable.

By the concurrent use of the ion exchange membrane electrode in addition to the sodium amalgam electrode, the ionic activity of sodium ion in salt‐free polyelectrolyte solutions was determined over a considerably wide range of sample concentration. As polyelectrolyte samples, several kinds of sodium polyvinyl alcohol sulfates differing in their degrees of esterification and degrees of polymerization (sodium polystyrene sulfonate, sodium cellulose sulfate, and carboxymethylcellulose) were used. The peculiar dependency of the activity coefficient of sodium ion upon the sample concentration first noted by Kern was confirmed with all samples in this study; that is, γNa+ decreases with dilution of the sample solution. Further, it was confirmed that the degree of esterification, viz., the charge density on a linear polymer, is a most important factor while the activity coefficient is entirely independent of the degree of polymerization. The influence of structure of the polymer skeleton upon the activity coefficient was found to be comparatively small. Some of the above results were discussed on the basis of the authors' theory published in a previous paper.

Some measurements of the electrophoretic velocity were carried out on sodium polyvinyl alcohol sulfates. The intrinsic mobility of the polyion in sodium chloride solutions was obtained by extrapolating the values at various polymer concentrations. The extrapolating value at the zero polymer concentration was the same for both descending and ascending boundaries. The mobility of polyion vs. sodium chloride concentration curve thus obtained showed the following features. (a) At zero NaCl concentration the mobility of polyion quite agrees with the mobility of the monomer acid. (b) In the limit of sufficiently concentrated NaCl solution, the mobility also approaches the mobility of the monomer acid. (c) In the intermediate state between these two limits, measured mobilities of polyion are always larger than the mobility of the monomer acid. Accordingly, there is a maximum of the mobility at a certain NaCl concentration. These experimental results were analyzed in terms of the theory of Hermans and Fujita on the electrophoresis of coiled polyelectrolyte, and it was found that their theory gives a satisfactory (at least qualitatively) explanation of our experimental data.

A new theory of strong polyelectrolyte solutions based upon the Poisson‐Boltzmann equation is presented. Assuming that the ratio of the effective charge of the macro ion to its original charge is very small, the Poisson‐Boltzmann equation is solved without adopting the Debye‐Hückel approximation. As a result of the calculation, the effective charge of the actual coiled macro ion with the strongly dissociative groups was found small enough to justify this assumption for the solutions of varying concentration over wide range. Moreover, the free energy, and consequently the chemical potential of the components, of the polyelectrolyte solution with or without simple salt are calculated. The idea of “ion fixation” is theoretically introduced as convenient for representing the state of the polyelectrolyte solution. The theoretical results obtained above are quantitatively compared with experimental data with very good agreement.