Bulk Synthesis of Phase-Separated Polyurethane Vitrimers by Slowing Down Cross-Linking at a High Catalyst Content

Phase-separated polyurethane (PU) vitrimers show great potential as sustainable materials due to their inherent dynamic reactions and excellent mechanical performance. However, their preparation often requires special moieties and a large amount of solvents, which severely limits their application. Herein, a simple strategy for the bulk synthesis of the phase-separated PU vitrimers was developed by combining the slow cross-linking process with the accelerated urethane exchange during polymerization. An NCO-terminated prepolymer was first synthesized, in which the catalyst dibutyltin dilaurate (DBTDL) and a thiol-terminated cross-linker were introduced for the following cross-linking process at high temperatures. Due to the slow formation of thiourethane and fast dynamic reactions of urethane at a high temperature and DBTDL content, the cross-linking process was slow, while the urethane exchange was accelerated, both of which could effectively promote the phase separation in the vitrimer. The phase separation can be adjusted by the preparation temperature and catalyst content. The phase-separated vitrimers showed improved mechanical performance, creep resistance, and strengthened recycling performance because of the aggregation of urethane bonds in the hard segment (HS) phase. This work shows great potential for bulk synthesis and optimization of phase-separated PU vitrimers, which would benefit their application.