Influence of soft block crystallization on microstructural variation of double crystalline poly(ether-mb-amide) multiblock copolymers

This work reports the crystallization behavior of a series of poly(ether-mb-amide) multiblock copolymer (PEAc) samples, composed of long-chain carbon polyamide 1012 (PA1012) as hard segments and poly(tetramethylene oxide) (PTMO) as soft segments. Rheological and dynamic mechanical results showed that PA1012-mb-PTMO multiblock copolymers are microphase segregated in the both melt and solid states, forming two partially miscible phases with distinct crystallization and glass-transition temperatures that depend on composition. The copolymers are probably in the weak segregation limit, as the PA1012-rich phase can break out and form spherulitic templates during cooling from the melt. For the PA1012-mb-PTMO copolymers with long PTMO segments, it was found that the crystallization of the PTMO-rich phase induced a variation in the long period as temperature decreased. This effect was related to the content of PTMO segments. At room temperature, only the PA1012-rich phase crystallized, whereas PTMrich phase remained amorphous within the interlamellar regions of the PA1012 spherulitic templates. Upon further cooling, the PTMO-rich phase crystallized forming crystalline lamellae located in between the adjacent PA1012 lamellae, forming double crystalline spherulites. Based on the research results, a schematic model was proposed to describe the multistage crystallization behavior of PA1012-mb-PTMO copolymers.