Enol Ethers Are Effective Monomers for Ring-Opening Metathesis Polymerization: Synthesis of Degradable and Depolymerizable Poly(2,3-dihydrofuran).

Enol ethers are widely used as quenching reagents for Grubbs catalysts. However, we report the surprisingly effective ring-opening metathesis polymerization (ROMP) of cyclic enol ethers, because the resulting electron-rich ruthenium alkylidene complex remains active towards metathesis of electron-rich olefins, despite its deactivation toward hydrocarbon olefins. We demonstrate the first example of ROMP of cyclic enol ethers, using 2,3-dihydrofuran as the monomer, producing a new type of degradable and depolymerizable poly(enol ether). The pol-ymers exhibited perfect regioregularity and their molecular weights can be regulated using the loading of Grubbs initiators or the use of a linear vinyl ether as the chain transfer agent. We also developed protocols to deactivate the catalyst following metathesis of enol ethers and cleave the catalyst off the result-ing polymers using H2O2 oxidation. The resulting poly(dihydrofuran) can be recycled to monomer via depoly-merization with Grubbs catalyst or degraded to small molecules by hydrolysis under acidic conditions. This work opens exciting opportunities for a new class of ROMP monomers that lead to degradable polymers.

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