Structure and structure formation of a main chain thermotropic polymer

Random copolymers containing 58% 4-hydroxybenzoic acid and 42% 2-hydroxy-6-naphthoic acid are able to display a three dimensional order with a degree of crystallinity of more than 60%. The crystals are far from being perfect: their enthalpy and entropy of transition are 10–20 times smaller than expected for a perfect crystalline state and the volume change on transition is negligible. The crystallization occurs in two steps: the first, which is completed within seconds, leads to a degree of crystallinity of ∼ 30%. The second, very slow, step, which corresponds apparently to postcrystallization, occurs over more than 10 7 s of annealing time and causes the degree of crystallinity to exceed 60%.