Phase separation in semicrystalline polymer blends and copolymers studied via thermal segregation and crystallization kinetics

The miscibility versus immiscibility in a crystalline two component system is discussed, based on phase separation and crystallization kinetics considerations. The thermal segregation was used to create or enhance the phase separation in crystalline two component systems. By comparing the crystallization kinetics before and after thermal segregation, one can distinguish two types of phase separation: (1) intrinsic phase separation in the melt for an immiscible system, or (2) phase separation induced via crystallization for a miscible system. Metallocene short-chain branching polyethylene (SCBPE) and nylon 6/polyimide triblock copolymer systems were taken as examples, and the phase behaviour determined via this thermal segregation and crystallization kinetics method. It is evident that the crystallization kinetics after thermal segregation are substantially faster than that before thermal segregation, and become much faster after keeping the sample in the melt for some time for the SCBPE system. Our results suggest that the molecules with different SCB contents in the SCBPE system may exhibit liquid–liquid phase separation in the melt. In contrast, studies on the crystallization kinetics of the nylon 6/polyimide system showed that nylon 6/polyimide triblock copolymer exhibits lower phase separation compared with in situ or solution blends. Thermal segregation and crystallization kinetics may serve as a very useful method to study the phase behaviour in semicrystalline blends and copolymers. © 2000 Society of Chemical Industry