Morphological, rheo-optical, and dynamic mechanical studies of a semicrystalline block copolymer

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Abstract
The morphology, rheo-optical behavior, and mechanical relaxation properties were investigated for a series of three segmented copolyesters containing blocks of crystalline poly(tetramethylene terephthalate) and amorphous poly(tetramethylene ether). Transmission and replica electron micrographs show that if cast from a hot solution of 1,1,2-trichloroethane on a heated surface, all the samples show distinct spherulitic structures. Annealing appears to increase the lamellar thickness. On the other hand, casting from a solution of 1,1,2,2-tetrachloroethane produced a film that showed no evidence of the presence of spherulites, although microphase separation persists and crystallites appear to be randomly oriented in the amorphous matrix. Small-angle light-scattering experiments for trichloroethane-cast samples confirmed the existence of spherulites. Dynamic mechanical data of these copolyesters show three principal relaxation peaks. These are the melting peak of the poly(tetramethylene terephthalate) block, the primary glass transition peak of the poly(tetramethylene ether) block, and the local mode relaxations of both blocks at low temperatures. Annealing and casting from different solvents did not affect the relaxation behavior of these copolyesters.