SAXS and DSC study of co-crystallisation of low molecular-weight PEO fractions in polymer blends

This study is aimed at a better understanding of co-crystallisation phenomena in PEO/PEO and PEO/ PEO-b-PPO-b-PEO blends in the course of crystallisation. Simultaneous real-time SAXS measurements and the DSC method were used for observing the development of the structure during isothermal melt-crystallisation and during linear cooling and subsequent heating. PEO/PEO blends. Binary mixtures of PEO (3000) and PEO (4000) were studied. During all temperature treatments, co-crystals are always formed. Under certain conditions a small amount recrystallises to another lamellar system. The thickness of the co-crystal lamellae depends on the composition of blends and crystallisation temperature, and increases with growing concentration of the higher-M W component (PEO 4000). During heating, on approaching the melting points of the components, all blends recrystallise giving a single, more stable co-crystal structure. PEO/PEO-b-PPO-b-PEO blends. During isothermal melt-crystallisation, two different lamellar systems, LP1 (with thicker lamellae) and LP2, are simultaneously formed in the neat copolymer and in blends with predominating copolymer content. This tendency gradually vanishes with the decreasing copolymer content. In blends with a majority of neat PEO, a single lamellar system is developed. In all blends, co-crystal systems are formed during crystallisation.