Influence of ethylene/propylene sequences on the thermal and mechanical properties of propylene‐based elastomers.

A range of industrial propylene‐based elastomers (PBEs) were investigated to disclose the relationship between the ethylene/propylene sequences distribution and the performance. The results of carbon‐13 nuclear magnetic resonance and Raman spectroscopy indicated that the majority of propylene sequences existed as isotactic polypropylene (iPP) segments and the stochastic insertion of ethylene sequences mainly in the form of ethylene–propylene (EP) segments. In this case, the amorphous EP chain segments joined by iPP crystals served as physical cross‐linking points, while the completeness of iPP crystallines was disturbed by the presence of ethylene sequences. Eventually, the ratios of imperfect short crystalline were gradually raised with the increasing ethylene contents, and even noncrystalline when the ethylene contents were higher than 15%. Accordingly, the features of these short crystalline networks played a decisive role of the mechanical properties of these PBEs. It was revealed that the higher contents of PPP segments led to more stiffness of PBEs. Therefore, the excessive insertion of ethylene sequences negatively affected the crystallization and mechanical performances of PBEs, and the optimal ethylene content was about 10%–15%. Additionally, in the case of similar molecular sequences, low‐molecular weight had adverse effect on strength or stiffness. [ABSTRACT FROM AUTHOR]