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Abstract:The geometric thermodynamics approach has been used for investigation of the possible glass transition point versus composition curves and their dependence on various parameters for both mixtures and systems with covalent bond between the components (block-, graft-and star-polymers) in which phase separation is possible. Predicted relationships are compared with the experiment. Conditions have been determined under which glass transition hinders the liquid-liquid separation.

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Coupling of demixing and glass transition in polymer blends and block copolymers having the liquid-liquid separation curves with both the upper and the lower critical separation temperatures is discussed. Particularly, in the latter case a transition from liquid to glassy state at increased temperature was found. Crystallization kinetics and morphology of polymer blends and block copolymers under superposition of demixing and crystallization was studied, and their interaction and coupling was found manifested in formation of various non-equilibrium morphologies and abnormal increase of crystallization rate at the separation boundary. The morphology is determined by the ratio of demixing and crystallization rates.

IntroductionFor experimental studies, polymer blends oer evident and substantial advantages because they are characterized by a slow mode of the phase separation. These advantages of polymer blends allowed identi®cation of nucleation and growth of droplet phases in metastable regions [1] as well as spinodal decomposition in unstable regions [2±5]. Theoretical investigations showed that, for o-critical mixtures, spinodal decomposition should take place at lower supersaturations compared with those predicted from the classical spinodal [6]. The boundary between the two modes of phase separation is referred to as a nonequilibrium percolation threshold (NPT), which takes an intermediate position between the regime of growth of isolated droplets or clusters and the regime of the development of a nonequilibrium percolation structure, which is produced at early stages of phase separation and, at late stages, breaks down into droplets. However, the lack of experimental data concerning phase separation in the boundary region between the two regimes is quite evident.The systems where the upper critical solution temperature is close to the glass transition temperature of one of the components involved in the polymer blend are more convenient for such an investigation for the following reason. Near the glass transition temperature, phase separation is aected by glass solidi®cation in one of the two phases. Within this phase, viscosity should dramatically increase with time, and phase separation should be noticeably retarded. This retardation allows the detailed characterization of the evolution of the polymer morphology at temperatures near the NPT, which usually escapes identi®cation in simple¯uid systems.We report our observations of a novel phase-separation phenomena in o-critical mixtures with a low volume fraction of the polymer phase (minority phase), whose glass transition temperature is close to the NPT. At supersaturations close to the NPT, spinodal decomposition is accompanied by a breakdown of the percolation network into individual rami®ed clusters, whereas at higher supersaturations far from the NPT no breakdown of the percolation structure is observed, and spinodal decomposition proceeds via the contraction of the percolation network to the center of the sample. In the latter case, at late stages of coarsening, the phase formed experiences a well-pronounced secondary phase separation.Abstract The nonequilibrium percolation threshold was shown to take an intermediate position between binodal and mean-®eld spinodal. Below the nonequilibrium percolation threshold, a bicontinuous phase structure was produced. This percolation structure, depending on supersaturation, breaks down to rami®ed clusters slowly assuming a spherical droplet form or contracts to the center of the sample. In the latter case, at late stages, secondary phase separation is observed.