Phase diagram and structural study of polystyrene — poly(ethylene oxide) block copolymers, 1. Systems polystyrene/poly(ethylene oxide)/diethyl phthalate

Abstract

AbstractBy means of low angle X‐ray scattering and differential scanning calorimetry, we have drawn the phase diagrams of poly(ethylene oxide)‐polystyrene block copolymers in the presence of diethyl phthalate as a preferential solvent of polystyrene.Such systems exhibit two liquid‐cristalline structures in terms of temperature and solvent concentration. At temperatures below about 50°C, a lamellar structure (LC) with crystallized poly(ethylene oxide) chains exists. Between 50 and about 170°C, we find a structure with melted poly(ethylene oxide) chains. Like for amorphous block copolymers, the type of the latter structure is governed by the copolymer composition.We have shown that in the LC structure, the poly(ethylene oxide) chains crystallize folding in two superposed layers, and we have studied the number of folds and the crystallinity of the poly(ethylene oxide) blocks as a function of solvent concentration, composition and rel. mol. mass of the copolymer, and of the crystallization temperature.