Preparation and properties of “thread‐through” copolymers of polyethylene with polyisoprene

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Abstract
Graft copolymers of polyethylene (PE) with polyisoprene (PI) were synthesized through polymerization of ethylene in toluene solution of PI (cis‐1,4‐:95%; 3,4‐:5%) using a homogeneous V(acac)3/Et3Al2Cl3 catalyst. Copolymers are formed when the growing polyethylene chains thread through the external and/or internal double bonds of the dissolved polyisoprene, giving copolymers with proliferating chain structures. Compared to the corresponding PI/PE blends, “thread through” copolymers had lower crystallization temperature, much lower crystallinity, and smaller microcrystallite sizes, indicating that the PI component hampered the crystallization of PE due to the chemical bonding between them. This chemical bonding between PE and PI was substantiated by a 11°C higher Tg of PI, 13°C lower α‐relaxation and the presence of a β‐relaxation, as compared to the corresponding PI/PE blends. Moreover, the PI/PE “thread through” copolymer with higher PI content had lamellar phase morphology, whereas the PI/PE blends with similar composition showed quite broadly dispersed PI domains. Much better mechanical properties of the “thread through” copolymers than of the PI/PE blends indicate that there is a great difference in their chain structures.