Bio-based Reprocessable Polyhydroxyurethane Networks: Full Recovery of Cross-link Density with Three Concurrent Dynamic Chemistries

Despite significant past efforts to improve the renewability and recyclability of non-isocyanate polyurethane (NIPU) networks, no previous study has attempted to achieve reprocessability of bio-based polyhydroxyurethane (PHU) networks. We have synthesized renewable, dynamic PHU networks by reacting bio-derived cyclic carbonates, carbonated soybean oil (CSBO) and sorbitol ether carbonate (SEC), with synthetic or bio-based diamines. With relatively mild reprocessing conditions, CSBO-based PHU networks exhibit complete recovery of cross-link density and associated properties after multiple melt-state reprocessing steps. Besides the presence of reversible cyclic carbonate aminolysis and transcarbamoylation exchange reactions, CSBO-based networks were shown via a model reaction to undergo a third dynamic chemistry: transesterification exchange reaction. In contrast to the excellent property recovery achieved by CSBO-based PHU networks, as a result of disadvantageous monomer molecular design, SEC-based networks exhibit poor reprocessability. This work reveals the effect of monomer structure on the reprocessability of dynamic polymer networks and highlights the effectiveness of CSBO to serve as a precursor of robust, sustainable NIPU networks with excellent reprocessability.