The use of a sulfonium-based photoacid generator in thiol–ene photopolymers for the controlled activation of transesterification through chemical amplification

Abstract

Chemical amplification consists of a cascade of reactions ranging from the photogeneration of an acidic compound to a change in the physical properties of a polymer. In our latest study, we envisaged that this route could be exploited for the on-demand release of –OH groups, with the aim of controlling the rate of bond exchange reactions in dynamic photopolymer networks. Following in the footsteps of our recent efforts, we herein propose a thiol–ene system comprising a sulfonium-based photoacid generator: upon UV-activation, the so-formed super acid cleaves dangling tert-butoxycarbonyl units present in the polymer chains, thus liberating hydroxy groups for the subsequent thermo-activated transesterification. We provide a comprehensive characterisation of the kinetics of the t-BOC deprotection step under different conditions of irradiation and thermal treatments. This laid the foundation for the analysis of the viscoelastic reflow of the examined systems, which we investigated and elaborated analytically. In particular, we combined a double Maxwell viscoelastic model with an Arrhenius–Rouse model to describe the stress relaxation kinetics of the examined systems, which has been rarely reported in vitrimers. We conclude that it is possible to implement a photo-latent onium salt to control the rate of stress relaxation and bond exchange in thiol–ene photopolymers. These efforts may contribute to rejuvenating the interest in chemical amplification by lending it the new guise of a powerful tool to control the macroscopic reflow of vitrimers.