Dynamical Observation of Structural Transition of Polymers Using an X-ray Diffraction System with Imaging Plates. 1. Reversible Helix/Helix Transformation of Poly(vinylcyclohexane)

Abstract

Two different crystalline forms were caused by drawing an unoriented isotactic poly(vinylcyclohexane) film, Form I and Form II, depending on the drawing temperature. Form II was changed into Form I thermally and Form I was converted into Form II by drawing. This reversible phase transformation was followed by dynamical X-ray observation. The X-ray measurements were carried out with an X-ray diffraction system with imaging plates, which was designed to record X-ray diffraction patterns over a series of short time spans while the samples were being heated or drawn. When samples were drawn at temperatures below about 110 °C, Form I was produced, and Form II was formed at higher temperatures. Through dynamical observations with the X-ray diffraction system, it was found that Form I occurred at an early stage of drawing independently of the drawing temperature and that the crystalline form was changed into Form II by further drawing at high temperatures, e.g., 130 °C. Form II was transformed into Form I by heat treatment at temperatures above 248 °C. When the heat-treated sample of Form I was drawn at, e.g., 133 °C, the crystalline form was transformed into Form II. Thus, the transformation of Form II into Form I occurred thermally at temperatures above 248 °C and the inverse transformation was induced by applying the stress at temperatures above about 110 °C.