The ring-opening polymerization of cyclic ketene acetals (CKA) by free radical or controlled radical mechanisms (rROP) attracts considerable research interest since it presents an alternative route for the synthesis of aliphatic polyesters. These monomers can indeed undergo radical addition on their C=C double bond that subsequently leads to propagation by ring opening. The CKA/vinyl monomer rROP appears as an elegant method to elaborate partially or fully degradable copolymers depending on the proportion of ester functions incorporated in the copolymer backbone. Although this approach seems promising, important limitations still remain. The unfavorable reactivity ratios of CKAs with traditional vinyl monomers like (meth)acrylics or styrenics (rCKA&lt;&lt; rvinyl) indeed leads to considerable discrepancy between the incorporated fraction of CKA in the copolymer and it initial fraction in the monomer feed. The particular reactivity of CKAs was originally explained by the strong nucleophilicity of the double bond. To promote radical addition onto nucleophilic olefins, electrophilic radicals are usually required. Surprisingly, vinyl acetate, whose propagating radical is nucleophilic, appears experimentally to be the best comonomer for a good incorporation in the polymer chain. Thanks to DFT Calculations, we are now able to understand the reactivity of the CKA and common vinyl monomer and in particular, we found first that vinyl ether appears the most favorable vinyl monomer to copolymerize with CKA to get random architectures whereas trifluoromethyl vinyl acetate (CF3VAc) should provide alternating copolymers. These structures were confirmed experimentally with reactivity ratios of 0.73 and 1.61 for the couple MDO/VE and values close to 0 for the couple MDO/CF3VAc (MDO for 2-methylene-1,3-dioxepane). The good understanding of the reactivity of CKA monomers that allow for the tunable incorporation of main-chain functionalities in the copolymer would open up exciting perspectives in the field of degradable materials for bio-related applications.

Radical ring-opening copolymerization of cyclic ketene acetals with vinyl monomers

2019 Spring National Meeting

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