Sequential two-stage polymerization for synthesis of isotactic polypropylene/isotactic polybutene-1 alloys: composition, morphology and granule growing mechanism

In this paper, a crystalline/crystalline polyolefin alloy - isotactic polypropylene/isotactic polybutene-1 (iPP/iPB) in-reactor alloy with spherical particle morphology - were synthesized by sequential two-stage polymerization using a spherical MgCl2-supported Ziegler-Natta catalyst. The iPP/iPB alloys obtained were mainly composed of isotactic polybutene-1, isotactic polypropylene and polypropylene-block-poly (butene-1) block copolymers, which occupied more than 95 wt% of the total alloy. A possible polymerization mechanism was proposed to explain the block copolymer formation. The morphologies of original alloy particles and n-heptane-extracted alloy particles were characterized by SEM and a particle growth model of iPP/iPB alloy was proposed to illustrate the sequential two-stage polymerization mechanism and active-species distribution during this process.