Free radical ring-opening polymerization

Since unstrained five- or six-membered carbocyclic systems normally undergo free radical ring-closing polymerizations, only highly strained cyclic monomers had been shown to undergo free radical ring-opening polymerization. However, since a carbon-oxygen double bond is some 50 kcal more stable than a carbon-carbon double bond, it has been found that a variety of four- to sevenmembered heterocyclic monomers will undergo extensive free radical ring opening polymerization. Among the monomers, that have been shown to undergo such ring opening on polymerization, can be included cyclic ketene acetals, cyclic ketene aminals, cyclic vinyl ethers, unsaturated spiro ortho carbonates, and unsaturated spiro ortho esters. These monomers will also undergo copolymerization with a wide variety of vinyl monomers with the introduction into the backbone of the resulting addition polymer of an ester, amide, keto or carbonate group. Such introduction will make possible the synthesis of functionally terminated oligomers, biodegradable addition polymers, polymers with enhanced thermal stability, and monomers that expand on free radical polymerization.