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) (PEG) in the homopolymer and in two triblock copolymers of poly(ethylene oxide)-polystyrene-poly(ethylene oxide) (PEO-PS-PEO). crystallized from the ordered melt, have been studied respectively with X-ray diffraction, optical microscopy and differential scanning calorimetry, theology. A multilayer lamellar structure with a spherulitic superstructure is formed by the crystallizable block, and the amorphous phase is incorporated in the interlamellar PEO regions. The amorphous midblock exerts no influence on the local structure of PEO but has a strong influence on (i) the crystallinity, (ii) the equilibrium melting temperature, and (iii) the thickness of PEO domains. Crystallization proceeds via nucleation and growth and is faster in the triblocks under conditions of equal supercooling. Shear has a pronounced effect on the shape of the crystallization process but little effect on the average times of crystallization. It is shown here that rheology can be used to obtain the equilibrium melting temperature in semicrystalline polymers.