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

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 (i PP)-based diblock copolymers was designed and synthesized by coordinative chain transfer polymerization using a dimethyl(pyridylamido)hafnium/[Ph 3 C][B(C 6 F 5) 4 ]/Al i Bu 3 catalytic system. The prepared diblock copolymers were composed of the regular i PP 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 i PP, 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 i PP-based copolymers. [Display omitted] • The isotactic polypropylene-based block copolymers consist of hard and soft blocks. • The 1,5-hexadiene incorporated in the soft blocks underwent the complete cyclization. • The i PP-based block copolymers exhibit both high yield strength and elongation at break. [ABSTRACT FROM AUTHOR]