Stereoselective Ring-Opening Polymerization of Lactones with a Fused Ring Leading to Semicrystalline Polyesters

Abstract

Monomer design is vital in the development of polymers with desired thermal and mechanical properties. Here, we prepared two monomers (M1, trans-octahydro-2H-benzo[b][1,4]dioxepin-2-one and M2, trans-octahydro-2H-benzo[b][1,4]oxathiepin-2-one) based on 1,5-dioxepan-2-one (DXO) and 1,4-oxathiepan-7-one (OTO) by incorporating trans-fused cyclohexyl rings. These monomers featured living ring-opening polymerization-yielding polymers with predictable molecular weights while maintaining low D̵ values. To gain a better understanding of the influence of polymer tacticity on polymer properties, a series of polymers with variable tacticities were prepared under various conditions. Their thermal property studies revealed that increasing the Pr value to 91% of P(M2) led to an emerging melting-transition temperature of 101 °C. Copolymerization of M1 and M2 allowed us to obtain a well-defined diblock polymer P(M2)-b-P(M1) and random copolymer P(M1-co-M2) with distinct thermal behaviors. Excitingly, oxidation of P(M2) resulted in an increase of the glass transition temperature from 18 to 112 °C. Hydrolysis of these polymers to corresponding hydroxyl acids and subsequent lactonization reactions enabled a closed-loop life cycle of P(M)s.