Structure of Crystallizable Polymer Solutions

Abstract

Visually transparent solutions of crystallizable polymers in wide concentration and temperature ranges contain supramolecular particles which are fragments of the most perfect crystallites of condensed polymer. Though the fraction of these particles is usually with in 0.001-0.1wt % of the total polymer, their presence in a solution of macromolecules severely affects its physicochemical and technological properties (performance) and complicates (or even does not allow) the application of structurally-sensitive research techniques (e.g. lights cattering, dynamic birefringence, etc.). The parameters of the first-level supramolecular particles (just after visual dissolution) depend on the conditions of dissolution, storage, and the preliminary treatment temperature of the polymer. In wide polymer concentration and temperature ranges, a second level of the supramolecular particles ensemble is formed, with characteristic features of crystallization. From the formation rate of the second-level supramolecular particles, a microliquidus curve for them can be plotted. The paper presents data for the poly (vinyl alcohol) + water system which lack the area of liquid-liquid phase separation. Supramolecular particles parameters (average sizes, numerical and mass-volume concentration) were determined by means of the turbidity spectrum method.

Phase Analysis of the Cellulose Triacetate-Nitromethane System

“…It should be noted that for polymer concentrations ∼5-11 wt%, the transition of the homogeneous system to its metastable state is preceded by the appearance of anisometric birefringent (in polarized light) fragments (Figure 1(a)). This could be regarded as a manifestation of fluctuation structures (which are not separate phases in their essence) owing to the critical retardation effect (with diffusion coefficient vanishing) ([2, pages 238-240], [12]). The shape of such long-lived heterophasic fluctuations differs from the usual quasispherical one, possibly because of intercompensation of the strong polymer-polymer and polymer-solvent interactions.…”

“…Such a different character of the temperature dependence of V τ at different stages of phase separation gives evidence for the complex type of phase separation in the system. The V τ (T) dependence is known to be represented by a smooth curve with no minima or maxima for the liquidliquid phase separation, where as for the liquid-crystal one, the function V τ (T) is of extreme character [2,12]. In the latter case, the right-hand branch of the V τ (T) dependence Figure 3: Estimation of the boundary temperatures of phase separation for the CTA-nitromethane system with a polymer concentration of 2 wt% by extrapolation of the direct (a) and inverse rates (b) of turbidity growth, calculated at the stage of intense τ changes (1, method 1) and from the initial fragment of the kinetic τ = f (t) curve (2, method 2).…”

“…(c = const) at extrapolation intersects the abscissa axis at the temperature of liquidus, whereas the left-hand one gives the vitrification temperature [12]. Probably, in the composition range with an extreme V τ = f (T) dependence (method 2), particles with either amorphous or highly oriented structure (e.g., of crystal or LC nature) originate at the first instant of time when the system transfers to its metastable state.…”

Кінетика Процесу Нітрування Крохмалю Нітратною Кислотою

“…Це можна пояснити продовженням взаємодії нітратної кислоти з найбільш досконалими фрагментами кристалічних областей (кристалітів), що присутні в розчині, але через розмір та кількість вже не впливають на його прозорість. Таке явище має місце в застосуванні до розчинів інших полімерів [26]. Важкістю розчинення та нітрування вказаних кристалічних формувань можна пояснити проблему досягнення теоретичного (N = 14.14 %) ступеня заміщення в нітраті крохмалю.…”

Fundamental Structural and Kinetic Principals of High Strength UHMWPE Fibers Production by Gel-Technology

“…A great contribution to understanding the nature of the association of macromolecules in dilute UHMWPE solutions and gels was made by J. Delmas [ 33 , 34 , 35 , 36 , 37 ], who studied the dissolution of UHMWPE reactor powders using a “slow” DSC—a very sensitive and stable calorimeter (Setaram, Lyon, France), in which it was possible to place a large cuvette, stir it, and heat it at a very low rate (1–3 K/h). As mentioned above, it was assumed that the stable network knots induced by shear and responsible for the “continuity” of the gel are of a crystalline nature, however, no melting endotherms at high temperatures were previously found on thermograms.…”