Latent reactive polyurethanes based on toluenediisocyanate-uretdione and polycaprolactones

This study deals with the key raw material of many latent reactive polyurethane adhesives and describes the reaction of a crystalline isocyanate compound, toluenediisocyanate-uretdione (TDI-U), with a polyol matrix, e.g. polycaprolactone (PCL). Mixtures of these compounds (PCL:TDI-U with molar ratio 2:1) were investigated under isothermal and dynamic conditions with rheology, differential scanning calorimetry (DSC) and infrared spectroscopy (IR). Isothermal measurements at 80 °C showed that the solvation of TDI-U is followed after 16 min by the polyurethane formation. Isotherm storages at 40 and 60 °C and the DSC analysis according to Kissinger [1] yield in an activation energy E a of the reaction of the free NCO-groups of the TDI-U with the OH-groups of the PCL of about 85 kJ/mol. The formed polyurethane contains uretdione rings, which are opened at temperatures higher than 150 °C. The solvation process of the TDI-U seems to be an important parameter in order to control and analyse latent reactive systems and has to be investigated in further studies.