The Use of Free Radical Ring-Opening Polymerization to Produce Biodegradable Polymers
Although ionic ring-opening polymerization of heterocyclic monomers and the Ziegler-Natta ring-opening polymerization of cyclic olefins by metathesis are quite common, free radical ring-opening polymerizations are quite rare. On the other hand, free radical ring-closing polymerizations are common. Since a carbon-oxygen double bond is some 40–50 Kcal more stable than a carbon-carbon double bond, it was reasoned that the formation of a stable carbon-oxygen could be used to promote free radical ring-opening polymerization. Thus it was shown that cyclic ketene acetals could be used to promote such polymerizations with the introduction of an ester group into the backbone of an addition polymer. Thus if 2-methylene-1,3-dioxalane (1) was treated with a peroxide at high temperatures, a high molecular weight polyester resulted.