Synthesis of Isotactic Polypropylene-Based Block Copolymers via Bridged Metallocene Catalytic System

To address the inherent limitations in impact resistance of isotactic polypropylene, strategic incorporation of ethylene monomers into polypropylene chains is implemented as an effective toughening modification strategy. In this study, the Me 2 Si(2-Me-4-PhInd) 2 ZrCl 2 /(Ph 3 C)B(C 6 F 5 ) 4 catalytic system is employed for ethylene-propylene copolymerization, with particular emphasis on elucidating the influence of alkyl-aluminum species on propylene homo-polymerization kinetics. Systematic evaluation of four distinct alkyl-aluminum compounds as cocatalyst reveals that tri-isobutyl-aluminum demonstrates optimal performance, achieving both the maximum polymerization activity (44.16 × 10 6 g mol −1 h −1 ). Ethylene-propylene block copolymers are synthesized via a sequential two-stage polymerization approach, copolymers exhibiting both distinctive thermal characteristics and superior macroscopic performance. Prolonged ethylene–propylene copolymerization duration induces notable structural evolutions in the block copolymers, proportion of flexible random copolymer segments increases, and weight-average molecular weight reduces from 21.15 × 10 6 to 10.83 × 10 6 g mol −1 accompanied by narrowed polydispersity (Đ from 5.18 to 4.02). Comparative studies with MAO-activated systems further reveal that the current catalytic system produced block copolymers with enhanced molecular weights ( M w = 34.11 × 10 4 g mol −1 ), tighter molecular weight distributions (Đ = 2.46), and elevated propylene content.