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The procedure of constructing phase diagrams of partially crystalline polymer-liquid systems, which is based on a difference in refraction indexes of a pure liquid and its solutions in partially crystalline and highelasticity polymer was proposed.It was shown in [1-4] that phase equilibria in partially crystalline polymer-liquid systems cannot be adequately refl ected by a diagram containing only one boundary curve describing dependence of melting points of polymer crystallites on the initial ratio of components of a binary mixture and taken (by analogy to the systems of two crystallizing low-molecular liquids) as a liquidus curve.Such diagram (Fig. 1) should contain at least one more boundary curve (line BD) refl ecting conversion of the initial two-phase polymer-liquid system into a singlephase system: a solution of a liquid in amorphous fi elds of a partially crystalline polymer. This is a phase line also in another sense. It is a right binodal branch refl ecting the extraction or osmotic equilibrium in a partially crystalline polymer-liquid system [4]. However, this is the fi rst sense, which is fundamentally important for understanding the essence of processes taking place in such system with a fi xed composition and variable temperature.Actually, let the binary mixture with a composition corresponding to point k is heated up to the temperature corresponding to point k 1 . In this case we shall meet two characteristics: the temperature Т Lp of the full dissolution of 0.4 weight fraction of liquid in amorphous fi elds of a polymer; the melting point Т mL of the last crystallite in the single-phase system of a polymer gel with grid nodes in the form of crystallites.Though line BD, which refl ects the dependence of Т Lp on the initial binary mixture composition, can be successfully constructed by results of a sorption experiment with excess liquid, it is methodologically important to have a possibility of its constructing by the direct determination of the temperature of conversion of a two-phase system into a single-phase system. The procedure described below allows us to do it. The procedure is based on the difference of refraction indexes of a swelling polymer and a liquid, which makes it possible to fi x the presence of this latter in the system by the presence of its meniscus.The difference in refraction indexes of coexisting phases decreases during the experiment fi rst of all due to the conversion of a pure liquid into a solution of polymer fractions in it, which do not participate in the formation of crystallites. Therefore it is expedient to extract preliminary these fractions from the polymer at a temperature close as much as possible to that corresponding to point B in the phase diagram (Fig. 1).Low-density polyethylene (LDPE) of 15083-020 grade (GOST 16377-77) with a melt index of 1.32 ± 0.2 g/10 min and a melting point of 111.2 ± 0.4°С used in this work was extracted by chemically-pure grade toluene at 64°С within 5 h.The installation (Fig. 2) consisted of magnetic stirrer 1 and thick-walled glass ...

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An experimental phase diagram of the isotactic polypropylene−camphor system is constructed using an original optical method. It considerably deviates from the dynamic diagram, which can be obtained using conventional differential scanning calorimetry (DSC), and contains an additional boundary line that describes camphor solubility in the polymer. An accurate phase diagram makes it possible to perform a detailed and consistent thermodynamic analysis of the DSC, optical, and scanning electron microscopy data on the cooling of prehomogenized mixtures of different compositions, which leads to the formation of capillary-porous bodies via thermally induced phase separation. The removal of camphor results in the formation of polypropylene membranes, the morphology and functional properties of which, such as the total pore volume, mean pore size, permeability coefficient, and breaking stress, appear to be highly dependent on the composition of the initial binary system. It is shown that thermally induced phase separation induces the formation of microscopic cracks in the studied membranes. The crack density decreases with the polymer content in the initial system, but at 53 wt % of polypropylene, the membrane becomes completely impermeable to isopropanol despite the presence of large ∼4 μm pores, thus questioning the perspectives of its practical use. In general, the study makes it possible to achieve a deeper understanding of the membrane formation process via thermally induced phase separation in the mixtures of semicrystalline polymers with low molar mass substances.

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