The Super Structure and Crystal Transition of Drawn Poly [p-(2-hydroxyethoxy)benzoic acid]

Abstract

Two types of the a (helical chain) and the β (planar zigzag chain) crystal phases have already been found in oriented samples of poly(p-ethyleneoxybenzoate) (PEOB). Dynamic mechanical, X-ray diffraction, birefringence and electron microscopic techniques were employed to determine the mechanisms or processes of the α → β crystal phase transition upon stretching above the glass transition temperature (80° C). The following results were found for the α → β crystal phase transition of PEOB. (1) Since there is no change of degree of crystallinity during phase transition caused by stretching, the α → β phase transition proceeds with the mechanisms of crystal-crystal transformation. (2) The β phase volume fraction converted from the a phase is proportionally correlated with the applied stress whereas the applied strain is not an important factor for determining the β phase volume fraction. (3) According to the morphological observation, the super structure of drawn PEOB is referred to the mechanical two phase model in which tie link constrains two neighboring crystalline parts. (4) According to the measurements of orientation, amorphous chains are not constrained and almost randomized upon stretching above the glass transition temperature. (5) The values of modulus, calculated on the assumption that stress is selectively concentrated on the tie link of the mechanical two phase model and that the α → β crystal phase transition occurs in this tie link, are found to be in good agreement with the observed values of modulus at various temperatures. From these results, it was concluded that the α crystal phase of PEOB transforms to the β crystal phase selectivily in tie link region as a consequence of stress concentration during stretching above glass transition temperature.