Metathesis polymerization of diynes cyclopolymerization

The metathesis polymerization of diynes having four single bonds between the triple bonds (dipropargyl compounds) yields cyclopolymers. The structural imits may contain a cyclohexene ring, eqn. (26a), or a cyclopentene ring, eqn. (26b), with the possibility of both in the same chain (see below). 

The diynes HC=C(CH2) C=CH ( = 2, 4, 6, 8) have also been polymerized. For n = 2, using NbCls as catalyst, the product is mainly trimer, but for n = 6 or 8, a polymer with a highly branched structure appears to be formed (Srinivasan 1988). For = 4, it is surprising to find that Mo(CO)6/HOC6H4-Cl-3 in toluene at 120°C causes polymerization rather than metathesis (cf. Section 10.2.1) the product is thought to be a cyclopolymer containing enchained cycloheptene rings (Vosloo 1991). 

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