The preparation of hybrid trimer by cyclo-oligomerization of TDI and HDI and its curing process with polyols to form elastic PU coating

The hybrid cyclic isocyanate trimer with appropriate functionality and good solvent tolerance which can be used as a building block to construct polyurethane (PU) coatings was prepared by cyclo-oligomerization of toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI). Among all the tested catalysts, the self-made catalyst 3-(trimethylammonio)propyl carbonate (Cat. 4) was found to possess enough catalytic efficiency to confirm the NCO conversion to reach about 50% with both high (1 wt%) and low (0.25 wt%) catalyst loading at low temperature (40°C). The IR and NMR results proved the formation of a hybrid trimer, while HPLC results showed hybrid TDI/HDI trimer predominated in the product and only trace amounts of TDI monomer (