Circular polyester design by gem-heterodisubstitution: valerolactone-based polymers with high ductility and excellent strength

Geminal disubstitution is a frequent focus of attention when designing monomers for the construction of recyclable polymers, but it is used for that purpose with two same substituents in cyclic monomers, which causes difficulty in producing polymers combining good strength and high elongation. Here we design a series of α,α-heterodisubstituted δ-valerolactones (δVL) with two different alkyl substituents at the α,α-position of δVL (VL^R1,R2) which, when combined with the parent δVL and gem-α,α-dialkyl substituted δVL with the same alkyl groups, provide a desired platform for exploring circular polymer design by focusing on the asymmetric substitution of monomers. These VL^R1,R2s allow both facile synthesis of polyester PVL^R1,R2s with strong/ductile synergistic performance in a living fashion and selective depolymerization of the PVL^R1,R2s to completely recover monomers under mild conditions (using a recyclable catalyst at 100 °C). PVL^Et,Pr is a semicrystalline, strong (ultimate strength = 39.9 MPa) and ductile (elongation at break = 331%) material. These notable mechanical properties are complemented by its superior barrier to oxygen and water-vapor permeation, relative to LDPE and PVL.