Polyhydroxyurethane covalent adaptable networks: looking for suitable catalysts

Various bases (DMAP, DBU, TBD, t-BuOK), acid (p-TSA), thiourea (TU) and organometallic Lewis acid (DBTDL) were investigated as potential catalysts for the preparation of polyhydroxyurethane covalent adaptable networks. Catalytic systems were first selected for their ability to promote cyclic carbonate aminolysis quantitatively (full conversion of cyclic carbonates) with few or no side reactions (urea formation). Selected PHU networks were extensively characterized using thermo-mechanical analysis (TGA, DSC, DMA and tensile test), rheology experiments (stress relaxation, frequency sweep), spectroscopy analysis (ATR-IR), swelling and reprocessing tests. Combining rheology, ATR-IR analysis and model molecular reactions, we suggest a catalyst-dependent exchange mechanism in which solely the organotin Lewis acid (DBTDL) was capable to promote transcarbamoylation in PHU efficiently with both secondary (major product of aminolysis) and primary alcohols and thus an efficient reprocessing.