Flowability of Ethylene-Propylene Copolymer in Situ-regulated by Long-chain Nonconjugated α,ω-Diolefin

In heterophasic copolymerization of propylene to high-impact PP copolymer, an emerging approach to control of the all-important copolymer particle morphology is in situ crosslinking the ethylene-propylene copolymer (EPR) by nonconjugated alpha,omega-diolefin. With the formation of crosslinking structure, pendant unsaturation structure supervened and its role was unveiled. This paper discusses the effect of pendant unsaturation structure on EPR's flowability. A series of EPR samples with increasing crosslinking degrees were synthesized by an MgCl2/9,9-bis (methoxymethyl) fluorene/TiCl4 catalyst and 1,9-decadiene of increasing concentrations. The copolymers were characterized by NMR, GPC, and DSC for chain structure, small amplitude oscillatory shear for linear viscoelasticity, and creep rheology for flowability. Increasing 1,9-decadiene concentration increased the EPR crosslinking degree monotonously; nevertheless, its effect on viscoelasticity was rather complex. Chain structure analyses reveal that in terms of effect on viscoelasticity, two opposite reaction processes are in progress in ethylene/propylene copolymerizaiton with in situ crosslinking by 1,9-decadiene, one being crosslinking itself, the other the accompanying fomation of pendant alpha-olefin unsaturations which are short chain-branching in essence. It is perceived that the sluggishness of Ziegler-Natta catalyst to sterically bulky alpha-olefin makes the progression of crosslinking lag behind that of short chain-branching, which accounts for the peculiar U-shape in EPR flowability and 1,9-decadiene concentration relation.