21.19 : 烯烃复分解聚合：开环复分解聚合（ROMP）

Recall that ring-opening metathesis polymerization, or ROMP, utilizes the olefin metathesis reaction to synthesize polymers.

ROMP involves strained cycloalkenes as substrates, such as cyclopentene.

The release of the ring strain upon open-chain product formation acts as a driving force for the reaction.

Initially, cyclopentene reacts with Grubbs catalyst, a metal carbene, and forms a metallacyclobutane intermediate.

Subsequently, the intermediate undergoes a ring-opening reaction to give a new substituted carbene.

This new carbene further reacts with another molecule of cyclopentene via a ring-opening reaction and extends the alkyl chain.

Repetition of these steps leads to the formation of an unsaturated polymer product.

Generally, the reactivity of cycloalkenes towards ROMP increases with an increase in the ring strain or a decrease in the ring size.

ROMP reactions are useful in synthesizing fully conjugated and highly unsaturated materials by retaining the unsaturation of monomers in the polymeric product.