Preparation of Well-Controlled Isotactic Polypropylene-Based Block Copolymers with Superior Physical Performance via Efficient Coordinative Chain Transfer Polymerization

作者：Huan Xin Gao, Lu Xu, Shangtao Chen, Bin Du, Yin Xiao, Yuze Kang, Kunyu Zhang, Chao Liu, Li Pan, Bin Wang, Zhe Ma, Yue‐Sheng Li · 发表于：Macromolecules · 年份：2022 · DOI：10.1021/acs.macromol.2c00886 · 被引用次数：44 · 研究领域：Organometallic Complex Synthesis and Catalysis、Advanced Polymer Synthesis and Characterization、biodegradable polymer synthesis and properties

The synthesis of isotactic polypropylene ( i PP)-based block copolymers by means of controlled isoselective polymerization of propylene with high turnover frequencies is an ongoing challenge in industry and academia. Herein, we report a new strategy for reversible coordinative chain transfer polymerization of propylene and propylene–ethylene with a pyridylamido hafnium/[Ph 3 C][B(C 6 F 5 ) 4 ] catalyst system and i Bu 3 Al as a chain transfer agent under conditions that were optimized so that the rate constants for chain transfer and chain propagation were similar ( k p ≈ k ct ). Using this new strategy, we could obtain i PP- b -poly(ethylene- co -propylene) and i PP- b -poly(ethylene- co -propylene)- b - i PP block copolymers with controlled molecular weights, hard/soft block ratios, and compositions via a continuous-monomer-feeding approach like that used in living polymerization systems. The polymerization reactions produced uniform block copolymers with previously inaccessible microstructures. The copolymers have both a semicrystalline i PP block ([mmmm] > 99%, melting temperature > 155 °C) and soft ethylene–propylene copolymer blocks (glass transition temperature < −30 °C), with tunable high molecular weights (∼210 kDa) and Schulz–Flory distributions (PDI < 2.5). These promising block copolymers possess dramatically improved tensile properties (30–50-fold increase in elongation at break) relative to those of the i PP homopolymer, whereas the yield strength and strength a...