Enhanced crystallization of the γ‐form of propylene–ethylene copolymer in its miscible blends with propylene homopolymer

BACKGROUND: How to promote the formation of the γ‐form in a certain propylene‐ethylene copolymer (PPR) under atmospheric conditions is significant for theoretical considerations and practical applications. Taking the epitaxial relationship between the α‐form and γ‐form into account, it is expected that incorporation of some extrinsic α‐crystals, developed by propylene homopolymer (PPH), can enhance the crystallization of the γ‐form of the PPR component in PPR/PPH blends. RESULTS: The PPH component in the blends first crystallizes from the melt, and its melting point and crystal growth rate decrease with increasing PPR fraction. On the other hand, first‐formed α‐crystals of the PPH component can induce the lateral growth of PPR chains on themselves, indicated by sheaf‐like crystal morphology and positive birefringence, which is in turn responsible for enhanced crystallization of the γ‐form of the PPR component. CONCLUSION: Crystalline/crystalline PPH/PPR blends are miscible and the crystallization of the γ‐form of the PPR component is largely enhanced due to the heterogeneous nucleation from the α‐crystals first developed by the PPH component. Our findings could provide an effective way in practice to obtain isotactic polypropylene copolymers rich in γ‐form. Copyright © 2009 Society of Chemical Industry