Dynamical observation of structural transition of polymers using an X-ray diffraction system with imaging plates .1. Reversible helix/helix transformation of poly(vinyl cyclohexane)

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 degrees 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 degrees C. Form II was transformed into Form I by heat treatment at temperatures above 248 degrees C. When the heat-treated sample of Form I was drawn at, e.g., 133 degrees C, the crystalline form was transformed into Form II. Thus, the transformation of Form II into Form I occurred thermally at temperatures above 248 degrees C and the inverse transformation was induced by applying the stress at temperatures above about 110 degrees C.