CRYSTALLIZATION KINETICS OF POLY(ETHYLENE OXIDE) IN POLY(ETHYLENE OXIDE) POLYSTYRENE POLY(ETHYLENE OXIDE) TRIBLOCK COPOLYMERS

The structure and crystallization kinetics of poly(ethylene oxide) (PE G) in the homopolymer and in two triblock copolymers of poly(ethylene oxide)-polystyrene-poly(ethylene oxide) (PEO-PS-PEO). crystallized fro m the ordered melt, have been studied respectively with X-ray diffract ion, optical microscopy and differential scanning calorimetry, theolog y. A multilayer lamellar structure with a spherulitic superstructure i s formed by the crystallizable block, and the amorphous phase is incor porated in the interlamellar PEO regions. The amorphous midblock exert s no influence on the local structure of PEO but has a strong influenc e on (i) the crystallinity, (ii) the equilibrium melting temperature, and (iii) the thickness of PEO domains. Crystallization proceeds via n ucleation and growth and is faster in the triblocks under conditions o f equal supercooling. Shear has a pronounced effect on the shape of th e crystallization process but little effect on the average times of cr ystallization. It is shown here that rheology can be used to obtain th e equilibrium melting temperature in semicrystalline polymers.