Abstract

The morphology and crystallization behaviour of random block copolymers of poly(butylene terephthalate) and poly(tetramethylene ether glycol) have been investigated. Single crystals have been grown in thin films crystallized from the melt. Well defined lamellae, exhibiting ( hkO) single crystal electron diffraction patterns have been observed in copolymers containing down to 49 wt% (0.83 mole fraction) poly(butylene terephthalate). WAXS and electron diffraction support a model of a relatively pure poly(butylene terephthalate) crystal core with the poly(tetramethylene ether glycol) (soft segment) sequences and short hard segments being rejected to the lamellar surface and the soft segment rich matrix. The lateral dimensions of the lamellae are determined by the number of hard segment sequences long enough to traverse the stable crystal size at the crystallization temperature. This leads to an initial population of crystals formed at T c and a second set of smaller crystals that grow from the short hard segment sequences upon cooling to room temperature. The result is fractionation by sequence length due to a coupling of the sequence distribution with the stable crystal size at the crystallization temperature.

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