On the Cyclopolymerization of 1,6-Heptadienes, and their Role as Poly(methylenecycloalkane)s in Stereoengineering and Block Copolymers

Abstract

The research presented herein, addresses key issues of homogeneous Group 4 single-site coordination polymerization (CP) catalysts for the production of polyolefins and polyolefin-like materials. Specifically, this research moves beyond the `one-catalyst one-material' paradigm to afford an array of amorphous polyolefin materials with high Tg from a single monomer. The multitude of microstructurally distinct materials available from a single starting olefin is attributed to stereoengineering: a technique, which reduces stereoblock length in a highly controlled fashion while retaining regioselectivity. The precatalysts employed in this work are previously reported Group 4 CS-symmetric or C1-symmetric pentamethylmonocyclopentadienyl amidinate complexes with the general formula {(η5-C5R5)M[N(R1)C(R2)N(R3)]-(Me2)} (M = Zr, Hf, R = alkyl, Me = methyl), which are activated by cocatalysts such as N,N-dimethylanilinium tetrakis(pentafluorophenyl)-borate ([PhNMe2H][B(C6F5)4]). Living CP of 1,6-heptadiene and stereoengineering of the subsequent poly(methylenecycloalkane)s with the above complexes reveal a variety of stereochemically controlled, yet amorphous, poly(methylene-1,3-cyclohexane) (PMCH) materials with Tg values as high as 101 °C. Similar polymerization techniques have been applied, for the first time with Sita group complexes, towards the CP of the heteroatom-olefins such as diallyldimethylsilane (DAS). The controlled CP and stereoengineering of DAS resulted in amorphous poly(3,5-methylene-1,1-dimethyl-1-silacyclohexane) materials with Tg values as high as 127 °C. The living character and tunable stereoblock lengths of PMCH provided the opportunity to explore the high Tg polyolefin as the `hard' domain (A segment) in pure polyolefin AB block copolymers, BCPs. Specifically, amorphous AB diblock copolymers were synthesized using poly(1-hexene) as the `soft' B block to afford a series of microphase-separated morphologies without the deleterious effects of crystallization. Microphase-separated morphologies for were also observed for ABA triblock copolymers using atactic polypropylene as the `soft' segment (B block) and primary component. The latter BCPs were found to exhibit thermoplastic elastomeric properties. The work described in this document provides a foundation for the further expansion of the currently-limited pool of monomers to include heteroatom-olefins for CP with the aforementioned Group 4 transition metal complexes. Moreover, the formation of well-defined pure polyolefin block copolymers serve as an important contribution to the development of new polyolefin architectures.