To improve the performance and reduce raw material costs, blocked isocyanates were prepared with mixture of blocking agents in many industries. Three blocked isocyanates (adducts) namely ε-caprolactam/benzotriazole- blocked 4,4′-diphenylmethane diisocyanate (MDI), toluene-2,4-diisocyanate (TDI) and 4,4′-dicyclohexylmethane diisocyanate (H12MDI) were synthesized. Six reference adducts were also prepared by blocking MDI, TDI, and H12MDI with ε-caprolactam (ε-CL) or benzotriazole. The reactions were carried out in acetone medium and dibutyltin dilaurate (DBTDL) was used as a catalyst. The progress of the blocking reaction was monitored by IR spectroscopy. De-blocking temperatures (dissociation temperatures) of these adducts were studied using DSC and TGA and the results were correlated. As expected, the thermal analysis data showed that de-blocking temperature of blocked aromatic isocyanates was lower than that of the blocked aliphatic isocyanates. The low de-blocking temperature of blocked aromatic isocyanate could be due to electron withdrawing benzene ring present in the blocked isocyanates. It was also found that benzotriazole-blocked adducts de-blocked at higher temperature compared with ε-CL-blocked adducts.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Organic Chemistry
- Polymers and Plastics
- Materials Chemistry