Efficient Preparation of Isotactic Polypropylene-Based Block Copolymers with Tunable Mechanical Properties: From Thermoplastics to Elastomers

Abstract

Olefin block copolymers (OBCs), which exhibit improved mechanical and thermal properties over conventional random copolymers, are high-performance polyolefin materials with promising applications in cutting-edge fields. Herein, we reported a series of isotactic polypropylene (iPP)-based OBCs with both high melting temperatures (Tms) and tunable mechanical properties, prepared via coordinative chain transfer polymerization, using a dimethyl(pyridylamido)hafnium/[Ph3C][B(C6F5)4]/AliBu3 catalytic system. The prepared OBCs were composed of a semicrystalline iPP segment with Tm > 146 °C and a propylene/α-olefin copolymer segment with comonomer content up to 17 mol %. The block microstructure of the OBCs was confirmed by gel permeation chromatography along with cross-fractionation chromatography. By properly tuning the block length and block composition, these OBCs exhibited tunable mechanical properties ranging from tough plastics (breaking strength reaching 26 MPa, elongation at break reaching 1170%) to ductile elastomers (breaking strength reaching 14 MPa, elastic recovery reaching 84%). The synthetic strategy of iPP-based OBCs in this study not only provides insights for academic research on block copolymers but also reveals great potential in the industrialization of high-value-added polyolefin materials.