Combining two comonomers with highly different equilibrium polymerization behavior offers the synthetic possibility to create random, isolated units along a main polymer chain. Our interest was to explore the possibility to afford a polylactide-based chain with random inclusion of α-amino acids by the use of organocatalysts that can operate under low reaction temperature. By thorough elucidation on the kinetic and thermodynamic features of the 3S,6S-dimethyl-morpholine-2,5-dione (MD) and L-lactide (LLA) copolymerization, we demonstrated that the system could be tuned to allow up to 13 % incorporation of isolated MD units along the polylactide chain with control over molecular weight (Mn≈ 7.3 kg mol-1) and low dispersity (≤ 1.27). The equilibrium monomer concentrations displayed high dependency on the catalyst of choice, solvent polarity and initial monomer concentrations. In this copolymerization system, MD behaved as an unstrained monomer with a large propagation barrier. This behavior ultimately led to reluctance of MD to homopropagate, and subsequently to a kinetically controlled incorporation of MD along the polylactide chain. These findings highlight the ability to promote the polymerizability of MDs under organocatalytic ring-opening copolymerization with LLA, and unlocks the potential of using mild reaction conditions for the selective incorporation of isolated α-amino acid units along a polyester backbone.

Organocatalytic ring-opening copolymerization of 3S,6S-dimethylmorpholine-2,5-dione and L-lactide: Route towards isolated α-amino acid moieties along the polylactide chain

2019 Fall National Meeting

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