Vitrimer-like acrylic glass with fast stress relaxation by high-speed carboxy exchange reaction

Abstract

We previously reported vitrimer-like acrylic elastomers in which the network structure was rearranged through high-speed carboxy exchange via the reversible conjugate substitution reaction of 2-(acyloxymethyl)acrylate. In this study, a similar chemistry was applied to vitrimer-like acrylic glass to investigate the effectiveness of the fast bond exchange reaction for a higher glass transition polymer with lower chain flexibility. The copolymer of methyl methacrylate and acrylic acid, derived from acid degradation of the tert-butyl acrylate unit, was cross-linked via a conjugate substitution reaction with 1,6-hexylene bis[(2-bromomethyl)acrylate]. Despite the high glass temperature, the obtained cross-linked acrylic glass doped with 1,4-diazabicyclo[2.2.2]octane (DABCO) exhibited fast stress relaxation with a relaxation time of 5.3 s at 140 °C. Fast stress relaxation led to excellent processability, affording a transparent, colorless film with a high modulus and tensile strength by hot-pressing within 2 min at 140 °C. A similar synthetic strategy was applied for the upcycling of a commercially available acrylic board, poly(methyl methacrylate). The hydrolysis and subsequent cross-linking reaction afforded a cross-linked polymer, which formed a transparent film after doping with DABCO. However, this film exhibited significantly slow stress relaxation, with a relaxation time of 136 s at 170 °C, probably because of the diffusion of polymer chains and DABCO restricted by long polymer chains.