Abstract
Polybutylene-naphthalene-2, 6-dicarboxylate (I) is the condensation product from 2, 6-naphthalene dicarboxylic acid and butane 1, 4-diol. X-ray diffraction revealed that two crystal structures coexist in I films which are uniaxially stretched and crystallized: one is the same, though oriented, crystal structure as that crystallized unoriented specimen, and the other is the structure only appeared by the stretching. The former and the latter are named A and B-forms, respectively. The content ratio of A to B depends on the conditions of stretching and heat setting. When the films are stretched at temperatures lower than 65°C and heat set under constant length, the content of both forms mainly depends on the stretching rate. When the temperature of stretching is higher than 65°C, the ratio of content depends on the drawing ratio and on the temperature of stretching. On the other hand, in the uniaxially stretched films, which would have mostly B if it is heat set in taut, B decreases and A increases if the film is heat set under free shrinkage. This phenomenon seems to be a transition from B to A, although imperfectly.
