Boosting the Reactivity of Bis-lactones to Enable Step-Growth Polymerization at Room Temperature

The development of a circular model for plastics is a major challenge, with polyesters as primary targets. Lactones are key monomers thanks to ring-opening polymerization, but their use in step-growth polymerization has remained so far scarce and challenging. Herein we report a powerful bis-(γ-lactone) (γSL) that was efficiently prepared on gram scale from malonic acid by Pd-catalyzed cycloisomerization. The γ-exomethylene moieties and the spiro structure greatly enhance its reactivity towards ring-opening and enable step-growth polymerization to proceed in a controlled manner under mild conditions. Using diols, dithiols or diamines as comonomers, a variety of regioregular (AB)n copolymers with diverse linkages and functional groups (from oxo-ester, to β-thioether lactone and β-hydroxy-lactame) have been readily prepared. Reaction modeling and monitoring revealed the occurrence of an original trans-lactonization process following the first ring-opening of γSL. This peculiar reactivity opens the way to regioregular (ABAC)n terpolymers, as illustrated by successive step-growth polymerization of γSL with a diol and a diamine.