Crystallization of Rigid Rod Polymer, Poly (<i>p</i>-phenylenebenzobisthiazole), from Dilute Solution

Abstract

Crystallization of a rigid polymer, poly (p-phenylenebenzobisthiazole) from dilute solution has been investigated using a transmission electron microscope. Quenching forms fibrillar crystals in which polymer chains are parallel to the fibril. These fibrils change into shish-kebabs by subsequent heat treatment in the solvent. Isothermal crystallization gives groups of parallel rod-like crystals of the same length, which appear like “rafts” on a lake. Molecular chains are oriented normal to the rod crystal. The width of the rodlike crystal is closely related to the avarage molecular length, especially in the low molecullar weight region. Due to dispersity in molecular length, many oriented rigid chains are present as cilia on the margin of the rod crystals. Primary nuclei are mainly composed of higher molecular weight component. At early stages of organization of the rafts, the growing rod-like crystals (mother crystals) accompany fragmental crystals whose growth rate is much faster than that of the mother crystals, because of preliminary supply of the oriented molecular chains from the mother crystals. The differnce in the growth rate finally makes all the rod-crystals into the same length within the individual raft. Nucleation density and crystal growth rate have also been measured as functions of temperature and molecular weight.