Ring-opening Polymerisation of Exocyclic Olefins

Apparently, the insertion of a /i,/i-disubstituted olefin (which exomethylenecy-clobutane is) into a Zr-alkyl bond with a quaternary Cp atom is so slow that the rearrangement shown in scheme (47) is the preferred process. 

The polymerisation of exomethylenecyclobutane may present interesting arguments to explain the lack of polymerisability of /1,/i-disubstituted acyclic olefins such as isobutylene according to the insertion mechanism in the presence of coordination catalysts. Probably, also in this case, /i-methyl transfer in species that may initially be formed by 1,2-insertion [scheme (48)] occurs much faster than the next monomer insertion  

It can be seen from scheme (48) that such a transfer, if it occurs, reduces the chance of the polyisobutylene chain growth. 

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