The crystal habit and morphology of polybutylene terephthalate and related copolymers

Abstract

The morphology and crystal habit of segmented copolymers of poly(butylene terephthalate) have been investigated. Single crystals have been grown from the melt in thin films of a 73% poly(butylene terephthalate) content copolymer. The crystals exhibit ( hk0) single crystal electron diffraction patterns which indexes to the alpha crystal form of poly(butylene terephthalate). The lamellae are bounded by (010) faces on the long edges of the crystals and (100) and (1−10) faces at the crystal tip. The c ~ ) axis of the unit cell (and hence the polymer chain) is normal to the lamellar surface. The preferred growth direction of the crystal is [21̄0]∗ which is parallel to the projection of the a ~ axis on the a ~ ∗− b ~ ∗ plane. The a ~ axis is inclined at 26° to the a ~ ∗− b ~ ∗ plane. The [2−10]∗ fast growth direction observed for the lamellae also corresponds to the radial growth direction observed in spherulites grown from the melt. The radiation lifetime (100 kV electrons, 23°C) of poly(butylene terephthalate) and poly(butylene terephthalate)-poly(tetramethylene ether glycol) copolymers was measured and found to be 150 C m −2, independent of copolymer composition.