Molecular weight control and end group functionalization of polynorbornene by Ni(II)-initiated polymerization of norbornene in the presence of ethylene and ɑ-olefins
High-molecular-weight vinyl-type polynorbornene (PN) was obtained in high yields by a highly active nickel-based phosphorane iminato complex in the presence of methylaluminoxane. Termination of norbornene polymerization by functionalized ɑ-olefins yielded soluble end group functionalized polynorbornenes of controlled molecular weight. The impact of the ɑ-olefins on yield and Mn depends significantly on the sterical situation at the olefins. No proof for the incorporation of the olefin at any other position than the chain end was observed. Considerations based on yields and Mn suggest that the Ni hydride species, which is most likely formed upon β-H elimination reaction in the scheme of olefin addition to the growing PN chain, initiates a new PN chain; in other words, chain transfer occurs through β-H elimination reaction.