Electron microscopy study of the structure of normal and abnormal poly(butylene terephthalate) spherulites

Normal and abnormal spherulites of polybutylene terephthalate cast from solution in HFIP were investigated by electron microscopy (CTEM and STEM). Both spherulite types crystallize in the α form. The crystallite is biaxial with its greatest polarizability directions Z and Y oriented along the molecular chain and perpendicular to it in the plane of the terephthalate residue. In the normal spherulites, the [ 2 10] * direction is parallel to the radius direction, so that both Z and Y directions are oriented tangentially (negative spherulites). In the abnormal spherulites, the [ 1 11] * direction is parallel to the radius, and this explains the observed abnormal light scattering pattern.