Chemically recyclable oxygen-protective polymers developed by ring-opening metathesis homopolymerization of cyclohexene derivatives

Abstract

•Successful ring-opening metathesis polymerization of cyclohexene derivatives •Elaborate design of functional cyclohexene monomers to control ring strains •Facile thermodynamic control of polymerization and depolymerization for recycling •Chemically recyclable oxygen-protective polymers with high hydrolytic stability The ring-opening metathesis polymerization (ROMP) of six-membered cyclic olefins has been a long-standing challenge due to their low ring strain energies (RSEs). Here, we achieved the homopolymerization of cyclohexene derivatives to produce oxygen-enriched, chemically recyclable polymers. The polymerization was enabled by utilizing elaborately designed cyclohexene monomers to increase the ring strain energy. Specifically, the 1,2-diol groups of vicinal trans-cyclohexene-diols were converted to carbonate groups for highly efficient and controlled polymerization. The resulting polymers, which have fused cyclic carbonate groups on the backbone, were hydrolyzed to generate hydroxyl-group-enriched polymers with a well-defined 1,2-diol structure at every sixth carbon. Closed-loop recycling was demonstrated by ring-closing metathesis depolymerization (RCMD) back to vicinal trans-cyclohexene-diols. Open-loop recycling was also possible by oxidative cleavage of the 1,2-diol group of the polymers, producing industrially useful α,ω-dicarboxylic acids. The chemically recyclable and structurally well-defined 1,2-diol polymers have high hydrolytic stability and excellent oxygen-protective properties. The ring-opening metathesis polymerization (ROMP) of six-membered cyclic olefins has been a long-standing challenge due to their low ring strain energies (RSEs). Here, we achieved the homopolymerization of cyclohexene derivatives to produce oxygen-enriched, chemically recyclable polymers. The polymerization was enabled by utilizing elaborately designed cyclohexene monomers to increase the ring strain energy. Specifically, the 1,2-diol groups of vicinal trans-cyclohexene-diols were converted to carbonate groups for highly efficient and controlled polymerization. The resulting polymers, which have fused cyclic carbonate groups on the backbone, were hydrolyzed to generate hydroxyl-group-enriched polymers with a well-defined 1,2-diol structure at every sixth carbon. Closed-loop recycling was demonstrated by ring-closing metathesis depolymerization (RCMD) back to vicinal trans-cyclohexene-diols. Open-loop recycling was also possible by oxidative cleavage of the 1,2-diol group of the polymers, producing industrially useful α,ω-dicarboxylic acids. The chemically recyclable and structurally well-defined 1,2-diol polymers have high hydrolytic stability and excellent oxygen-protective properties.