One-Step Synthesis of Multi-Block Copolymers of Isotactic Polypropylene (iPP) and Theoretical Studies on the Regioselectivity and Stereoselectivity of Polypropylene

Abstract

For multi-block copolymers, using a one-step synthesis route can avoid repeating addition of monomers during the reaction, thereby preventing the contamination of polymerization reaction and the accidental termination of the polymer chain. For this purpose, described herein is a simple and efficient approach for synthesizing topological structure multi-block copolymers of isotactic polypropylene by copolymerizing ethylene, propylene and higher α-olefins by [N, Si, N, P] multi-chelated complexes ({P(C₆H₅)₂-N(C₆H₅)-(CH₃)₂Si-N-2,4,6-(F)₃C₆H₂}ZrCl₃). In this contribution, the complexes are found to exhibit high polymerization activity (up to 9.5 × 10⁶gP (mol ∙ Zr)⁻¹ ∙ h⁻¹) and relatively high incorporation content of 1-octene (up to 15 mol%). Density functional theory (DFT) was used to study the mechanism of copolymerization reaction. The results showed that propylene monomer is more prone to 1,2-insertion in kinetics to obtain iPP. Different lengths of iPP segments in the copolymer (terpolymer) chain not only led to different melting points but also block the terpolymer of propylene, ethylene and higher α-olefins. Enhancing α-olefins and ethylene units within the copolymer chain will also destroy the layered polypropylene crystals. Furthermore, the crystallizable polyethylene segment was not observed, implying that ethylene only participates in forming the random segments in the copolymer chains. Most importantly, polypropylene thermoplastic elastomer with good elasticity can be produced by the copolymerization of propylene with ethylene and 1-octene.