Changes in solutions of ultra-high molecular weight polyethylene Hostalen GUR in I ,2,4-trichlorobenzene with time were studied by means of viscometry and light scattering. The decrease of viscosity during ageing indicates that both the degradation of polyethylene chains and destroying of aggregates may occur. The former fact makes questionable the ultra-high molecular weight character of the sample.

A combination of several methods and quantitative parameters (fraction p of immobilized monomer units, apparent molecular weight, and size, number, and concentration of aggregates) as a function of time, temperature, and polymer concentration were used to obtain data characterizing aggregation of syndiotactic poly(methyl methacrylate) in n-butyl acetate. The thermal history of the sample (viz., the content of surviving nuclei which were identified with aggregates of globules formed during the intramolecular condensation) was shown to be decisive for the setting in and steepness of the aggregation process. Another "hysteretic" effect has been found by NMR for the equilibrium value of p at elevated temperatures. Regarding all experimental and reported data, a plausible qualitative model of aggregation was suggested; three processes, "globulation", nucleation, and flocculation, were recognized and characterized.

No abstract

The refractive index increments of polyacrylamide for various wavelengths were determined both in the usual solvents (water, ethylene glycol, formamide) and in those so far unused (ethanolamine, dimethyl sulfoxide). The values thus obtained are compared with the reported data. The necessity to employ anhydrous polyacrylamide samples is stressed. The question of the possible effect of ageing of solutions on the refractive index increment values is discussed. No ageing of solutions was observed at room temperature; at elevated temperatures, the amide groups of the polymer undergo hydrolysis in water. 1 wt.-%, and the molar mass determined by light scattering gave M , = 1 , l . lo6 g/mol.Redistilled water was used for differential refractometric measurements; the other solvents (dimethyl sulfoxide, ethanolamine and formamide) were distilled on a laboratory column and their purity was checked by gas chromatography. Commercial ethylene glycol and organic acids (analytical grade) were used without further treatment.

No Absrract.