“Ring-opening metathesis polymerization of structural diverse bicyclic amide-containing monomers to chemically recyclable, degradable, and mechanically enhanced polyolefins” by Subin Shin, Youngho Kim, Myungeun Seo, and Cheoljae Kim was published in Macromolecules. This work was collaborative research with the Kim group at Chungbuk National University.

Polyolefins are the most widely used plastics with excellent mechanical integrity and chemical resistance. However, their chemically inert hydrocarbon structures limit functionalization and degradation. Ring-opening metathesis polymerization (ROMP) has emerged as a powerful synthetic tool for preparing functional polyolefins with degradable and polymerizable characteristics by rationally designing cyclic olefin monomers with target functionality and balanced ring strain.

In this study, the Kim group selectively synthesized structurally distinct amide-containing bicyclic monomers in bridged or fused ring structures via the intramolecular Aubé-Schmidt reaction. ROMP of these monomers produced polymers containing amide bonds in the main chain. Highly strained bridged monomers enabled molecular-weight control by adjusting the monomer-to-catalyst ratio. The low ring strain of a fused monomer enabled chemical recycling via ring-closing metathesis depolymerization (RCMD). The recovered monomer was successfully repolymerized to afford a polymer with molecular weight and thermal properties comparable to those of the original polymer. Polymers derived from fused monomers also exhibited degradation via hydrolysis under acidic and basic conditions.

From a structural perspective, these bicyclic amide-containing monomers offer opportunities to control interchain interactions via hydrogen bonding and steric effects when copolymerized with other cyclic olefins. We found that their polycyclooctene copolymers exhibited substantially increased tensile strength and stretchability while maintaining a comparable modulus. The tough and stretchable behavior of the copolymers was quite different from brittle polycyclooctene, suggesting that the sterically demanding repeating units reduced the crystallinity of polycyclooctene. The copolymers retained degradable and depolymerizable features. These results highlight the potential of amide-containing bicyclic monomers as functional comonomers to enhance polyolefin mechanical properties while imparting degradability and chemical recyclability.

Read the full article here: https://doi.org/10.1021/acs.macromol.6c01722

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