No abstract

The isothermal rise in supermolecular order (SMO) in aqueous solutions of poly (vinyl alcohol) (PVA) over a wide range of temperature and concentration and also under shear has been studied. SMO was characterized by the equivalent average radius of super‐molecular particles (SMP) rΛ, estimated by the turbidity spectrum τ = τ(Λ). The methods of gradient dependence of viscosity electron and polarize‐optical microscopy, and light scattering according to Debye‐Zimm have also been used. It is shown that the process of isothermal rising of SMP over a wide range of temperature and solution concentration consists of two distinct stages: a relatively rapid rise and then a slow rise of SMP. In aqueous PVA solutions SMO represents, generally, the hierarchy of some its levels. The first level is considered to be the supermolecular particles, which form after the dissolution of the whole polymer mass. The character of this level is determined by the microstructure of the sample in the condensed state and dissolution conditions. The particles of the first level are the heterogeneous formation nuclei of the second level–particles of the fibril type. Fibrils, which have risen from the solution at high temperature (T ≥ 80°C) have shown the ability to aggregate into anisodiametric structures as the solution cools. These aggregates, determined to be the third level, are very sensitive to temperature. In turbulent shear the rising rate of SMO increases greatly as the characteristic concentration is made smaller. The results obtained give us reason to conclude that the rise in SMO in aqueous PVA solutions is due to the crystallization of macromolecules when the low molecular weight component is available.

The temperature dependence of the second virial coefficient, A2, in an aqueous solution of poly (vinyl alcohol) (PVA) has been studied by the light‐scattering method within the temperature range from 20 to 130°CC. The experiment was carried out under conditions which rule out the aggregation of macromolecules. The temperature dependence of A2 has the form of an extremum with an unpronounced minimum between 80–90°CC. In the temperature region studied here, A2 > 0, this condition is regarded as a proof of the stability of the system with respect to amorphous separation. Consequently, the supermolecular order which forms in the PVA‐water system over this range of temperatures (see Chem. Abst, (1967), 66: 11295u; (1971) 73, 56516x; (1971) 74, 23183d) has a crystalline nature. The literature noting an increase in the degree of sweiling with increasing temperature in the PVA‐water system in the interval 20–80°CC, which seems contradictory to a decrease in the solvent power (decrease in A2), may be explained by a decrease in the degree of crystallinity (degree of physical crosslinking) of the polymer.

The process of formation of the supermolecular order (SMO) in aqueous solutions of poly(vinyl alcohol) (PVA) has been studied by the method of turbidity spectrum in a turbulent flow produced by a blade stirrer rotating at a rate of 1,500 rpm. The kinetics of SMO formation has been investigated depending upon the polymer molecular weight (Mw) and concentration (C) and temperature (T) of the solution. The rate of formation of SMO was characterized in the first stage of the process by a relative increment in τ at 540 nm per hr. The concentration dependence, K = K(C), is extremal in character having its maximum at C = 0.5–1 g/dl. When T was increased from 20 to 50°CC, K decreased, whereas average equivalent size of supermolecular particles, rλ, remained unchanged. The colloid disperse phase of supermolecular particles (SMP) appears to be in a quasi‐equilibrium with the molecular‐disperse solution, since, after removal of SMP, the process of formation of SMO is resumed at the same rate. To a greater extent the character of SMO formation depends on the chemical structure of PVA (K drops off to zero with increasing content of the acetate groups up to 7.6%) and physical prehistory of the PVA sample (an increase in K after thermal treatment of the polymer in the condensed state). PVA films cast from stirred solutions revealed (by IR spectra) a greater degree of crystallinity then those cast from unstirred solutions. All other conditions being equal, K in a turbulent flow is higher by one to two orders of magnitude than K under static conditions. The data obtained have been explained from the point of view of crystallization of PVA when intensified by the turbulent regime of solution stirring.

A new modification of the method of turbidimetric titration based on taking the turbidity spectrum in the process of titration (accordingly designated “spectroturbidimetric titration” (STT)) has been proposed. STT permits the mass of the precipitated polymer Mγ to be determined in the process of titration with any change in the degree of dispersity of the precipitated polymer phase. The standardized plotting of the curve of solubility (CS) Mγ/(Mγ)max = f(γ), where γ is the volume ratio of the precipitator, proved to be independent of the nature of possible variation of the relative refractive index of the particles m = m (γ). STT was carried out with the commercial type of polystyrene (PS) (benzenemethanol) and withanionic poly‐α‐methylstyrene(P‐α‐MS) (cyclohexane‐octanol)in the serial turbidimeter FET. The turbidity was measured using five light filters at 4000–6000 Å. The speed of stirring was 64 rpm. Four rates of the precipitator input: W = 0.09, 0.20, 0.41, and 1.03 ml/min were used. Worse reproducibility of the colloid system structure in parallel experiments was found under low W correlated to the best division according to molecular weights. The STT method balanced these two antagonistic principles (like some others, though). Dependence on W of CS has been found. Graphic extrapolation of CS (with fixed Mγ% and W → 0) permitted the equilibrium CS to be determined. In a typical case three characteristic ranges of particles size changing in the process of titration were observed: decreasing (a reduction in gigantic fluctuations), a stable range, and increasing (particles coagulation). The colloid system structure may be regulated by selection of tiration conditions.