PHASE-BEHAVIOR AND MORPHOLOGY OF POLY(ETHYLENE OXIDE) BLENDS

Crystallization studies on blends of high and low molecular weight pol y(ethylene oxide) (PEG) have been carried out to characterize phase be havior and morphology. At low crystallization temperatures, both compo nents cocrystallize into a common crystal lattice. The thickness of th e cocrystal is found to vary with the blend composition. At high fract ions of the low molecular weight polymer, the cocrystal is thin, sugge sting a folding of the long-chain polymer into the lattice of the low molecular weight chain. At lower fractions of the low molecular weight polymer, the cocrystal is thicker, resembling the higher molecular we ight polymer. At higher crystallization temperatures, the components f orm a defective cocrystal which dynamically phase splits into its comp onents. The crystal transformation in the blend occurs by thinning of low molecular weight chains and thickening of high molecular weight ch ains. The formation of crystal templates of both components eventually results in phase-segregated growth. Models for cocrystallization and dynamic phase separation of components are discussed. A time-resolved small-angle X-ray scattering study along with complementary calorimetr y and optical microscopy results confirms the mechanism of cocrystalli zation and dynamic phase separation in PEO blends.