Preparation and characterization of isotactic polypropylene-based block copolymers with cyclic units

Abstract

Olefin block copolymer is one class of promising high-end material that has the potential to combine the performance advantages of individual blocks. In this work, a series of isotactic polypropylene (iPP)-based diblock copolymers was designed and synthesized by coordinative chain transfer polymerization using a dimethyl(pyridylamido)hafnium/[Ph3C][B(C6F5)4]/AliBu3 catalytic system. The prepared diblock copolymers were composed of the regular iPP segments and the propylene/1,5-hexadiene (1,5-HD) random segments. The incorporated 1,5-HD existed exclusively as methylene-1,3-cyclopentane units in the polymer chains, because of the complete cyclization selectivity of the employed dimethyl(pyridylamido)hafnium catalyst. These block copolymers possessed high melting temperatures over 158 °C. Moreover, the block copolymers exhibited remarkably improved mechanical properties with respect to iPP, which could be systematically tuned by adjusting the content of 1,5-HD. In the 1,5-HD content range of 3.4–11.0 mol%, the block copolymers exhibited both high yield stress and high elongations at break. The copolymerization approach of block copolymers provided an effective method to achieve the strength-ductility balance of iPP-based copolymers.