Methylenecyclopentane polymer

In the case of cyclopentene polymerization, the insertions at secondary alkyls are the only possible mode of chain growth no insertions adjacent to tertiary carbons are observed. For substituted cyclo-pentenes, there are more options in the polymerization. For instance, with 4-methylcyclopentene, insertion generally takes place on the unsubstituted side of the ring. This leaves a cis-C—H bond available for chain walking to the methyl group. The next insertion takes place at the primary carbon atom, giving a methylenecyclopentane polymer as illustrated in eq 8. A similar behavior is observed for... 

The second termination reaction is alkyl chain end transfer from the active species to aluminium [155]. This termination becomes major one at lower temperatures in the catalyst systems activated by MAO. XH and 13CNMR analysis of the polymer obtained by the cyclopolymerization of 1,5-hexadiene, catalyzed by Cp ZrCl2/MAO, afforded signals due to methylenecyclopentane, cyclopentane, and methylcyclopentane end groups upon acidic hydrolysis, indicating that chain transfer occurs both by /Miydrogen elimination and chain transfer to aluminium in the ratio of 2 8, and the latter process is predominant when the polymerization is carried out at — 25°C [156]. The values of rate constants for Cp2ZrCl2/MAO at 70°C are reported to be kp = 168-1670 (Ms) 1, kfr = 0.021 - 0.81 s 1, and kfr = 0.28 s-1 [155]. 

Scheme 68 illustrates cyclopolymerization of 1,5-hexadiene catalyzed by a homogeneous chiral zirconocene complex to form optically active poly(methylenecyclopentane), whose chirality derives from configurational main-chain stereochemistry (757). This polymer is predominantly isotactic and contains predominantly trans cyclopentane rings. 

---