Bulk Thermal and Transition Behavior

In any case, the general transition behavior is quite consistent with the notion of separation into two phases one, crystalline PEO the other, glassy PS. Further, the separation must be essentially complete, for the glass phase obviously exists in the presence of the molten crystalline phase (7 7 ). (It should be pointed out that a case in which 7 has never been observed for homopolymers.) The particular finding here, of course, reflects the existence of two phases, each behaving nearly independently with respect to transition temperatures. 

Several other features of the transition behavior are worth noting. First, both the DSC and dilatometric experiments revealed the existence of two crystallizing temperatures, about 60 C apart, for copolymers rich in 

PS (w 0.6). This phenomenon may be attributed to the occurrence of both heterogeneous (T 50-60°C) and homogeneous (7 — 20°C) nucleation. Thus, when domains of PEO are of molecular dimensions, and are dispersed in a matrix of glassy PS, some domains contain heterogeneous nuclei and some do not. Since most crystallization appears to be homogeneously nucleated, the domain size must in fact be small and discontinuous (Kovacs, 1967). 

In summary, the thermal behavior of the PEO-PS block copolymers can be accounted for in terms of a phase separation into domains of PEO and PS. However, the existence of a matrix and the interconnection between the domains appear to influence the behavior of the domains themselves. The phenomena observed are certainly worth much further study. 

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