Trialkylsulfonium-Based Reprocessable Polyurethane Thermosets

We report the development of a solvent-free protocol to produce colorless, highly transparent, and glassy polyurethane-based networks containing thioether bonds using commercially available building blocks. These polyurethane networks are converted into reprocessable networks by partial alkylation of the thioether bonds, giving dynamic trialkylsulfonium bonds that are able to exchange via transalkylation at elevated temperatures, thus inducing viscoelastic flow. Reprocessability of the trialkylsulfonium networks was demonstrated for three cycles without significant degradation of material properties. Interestingly, these materials were found to be highly processable at elevated temperatures (∼140 °C) and showed excellent creep suppression up to 100 °C, a combination that is rare among dynamic covalent polymer networks. The suppression of creep can be further controlled by changing the alkylating additive. In addition, as a result of their excellent transparency and high clarity, we investigated their optical properties to assess their potential use in smart coatings and optical devices.