Vitrimers based on block copolymers with diverse block sequences

Abstract

Vitrimers based on block copolymers give access to adaptable polymer networks where the resulting properties can be adjusted not only by the vitrimer chemistry itself but also can be influenced by the structure of the block copolymer. In this work, linear AB, ABA, and BAB block copolymers are introduced as backbones in vinylogous urethane vitrimers to produce crosslinked materials that are reprocessable and have a wide range of tunable mechanical properties. The narrow-disperse block copolymers were synthesized by photoiniferter reversible addition-fragmentation chain transfer polymerization (photoRAFT). Two different types of hydrophobic A blocks, poly(methyl methacrylate) and poly(ethyl methacrylate) with a higher glass transition temperature compared to the hydrophilic B block, poly(2-hydroxyethyl methacrylate), were chosen. The B block carries the functional groups for further modification to obtain acetoacetylated side groups, which are then transformed to vinylogous urethane crosslinks. It has been found that the architectures of backbones as well as the alkyl substituents in the side groups of the A block influence the final performance of the vitrimers. By adjusting block sequences, the mechanical properties can be varied from hard to tough to elastic materials corresponding to BAB, ABA, and AB block copolymer vitrimers, respectively. These materials are reprocessable and have self-healing as well as shape-memory properties.