Cyclopentene polymerisation mechanism

A plausible polymerisation mechanism that accounts for the 1,3-enchain-ment of cyclopentene, leading to both cis- and tram-poly (l,3-cyclopentylene)s, is outlined below [15,19,20] ... 

Note the chain end stereocontrol mechanism operating in cyclopentene polymerisation, which is similar to norbornene polymerisation but differs from the case of norbornene in the fact that in cyclopentene polymerisation the chiral centres of the growing polymer chain are located in the a and y position [15]. 

For didactic reasons we will not show mechanistic proposals that have been abandoned, because the carbene mechanism now7 is well established. It is referred to as the Chauvin-Herisson mechanism, as they were the first to propose the intermediacy of metal-alkylidene species [5], Their proposal was based on the observation (simplified for our purposes) that initially in the ringopening polymerisation of cyclopentene in the presence of 2-pentene a mixture of compounds was obtained rather than the single products if a pair-wise reaction of cyclopentene (or higher homologues) and 2-pentene would occur. Figure 16.3 shows the results. 

Interesting evidence supporting the mechanism of polymerisation of acetylenes via carbene species is provided by the block and random copolymerisation of acetylenic monomers with cycloolefins. For instance, block copolymers of acetylene and cyclopentene with the WC —AlEtCT catalyst [41] and block copolymers of acetylene and norbornene with the (MeA. Oj2W(=NAr)= CHMe3 catalyst [42] have been obtained moreover, random copolymers of phenylacetylene and norbornene with the WC16 catalyst have also been obtained [149, 150],... 

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