Comparison of chain structure and morphology of an olefinic blocky copolymer and a Ziegler–Natta‐based ethylene random copolymer

Abstract

AbstractThe microstructure and morphology of an olefinic blocky copolymer (OBC) and an ethylene‐hexene copolymer prepared by conventional Ziegler‐Natta catalysis (ZNEH) are compared. It is found that these two samples have similar melting temperatures, but the overall comonomer content in OBC is slightly higher. The crystallization temperature and crystallinity of OBC are markedly lower than those of ZNEH. A successive self‐nucleation annealing experiment reveals that OBC has a more uniform distribution of crystal thickness, indicating a more homogeneous composition distribution in its hard blocks. Small‐angle X‐ray scattering (SAXS) results show that the long period of OBC hardly changes with temperature in the low‐temperature range, whereas that of ZNEH increases gradually with temperature due to melting of the less perfect crystals. The average lamellar thickness of crystals is larger for OBC than for ZNEH, but the thickness of the thickest crystals is comparable in the two. The SAXS profiles were analyzed using a one‐dimensional correlation function. The result reveals that the partially ordered interphases in OBC are mainly located at the interface of the crystalline and amorphous phases. In contrast, the interface of the crystalline and amorphous phases in ZNEH is quite sharp and it is inferred that the partially ordered interphases are distributed in the bulk as separated domains. Scattered tiny crystals are formed in ZNEH, but OBC exhibits a macroscopic morphology of large spherulites. It is also observed that more amorphous phases are rejected outside of the lamellar stacks and spherulites in OBC. © 2012 Society of Chemical Industry