Synthesis and characterization of polyurethanes using 4-bromo-1H-pyrazole as a blocking agent

Polyurethanes, an important class of polymers, are used extensively for preparing various apparel, shoesoles, etc. This paper reports that polyurethanes could be prepared conveniently after blocking the precursor molecule toluene diisocyanate (TDI)with 4-bromo-1H-pyrazole to form blocked toluene diisocyanate (TDI). The blocked adducts were characterized by FTIR, NMR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and CHNS analysis. Particularly, spectroscopic analysis was used to confirm the complete blocking. The DSC thermogram showed that the blocked adducts deblock at 238 degrees C, regenerating TDI and blocking agent 4-bromopyrazole. At 238 degrees C, regenerated TDI reacted with polyolsof different molecular weights to form polyurethane under solvent-free conditions. The polyurethanes were further characterized by FTIR, NMR, thermogravimetric analysis, differential scanning calorimetry, and contact angle study. FTIR study shows that there is no peak at 2250-2270 cm(-1). So it confirms the absence of NCO peaks. Contact angle measurements of various polyurethanes showed the values in the ranges of 27-50 degrees C, indicating generally hydrophilic natures of samples. DSC thermogram indicates the presence of glass transition temperature of synthesized polyurethanes at - 30 to - 40 degrees C. Viscosity measurements of polyurethanes in chloroform at different temperatures indicated decrease in viscosity at higher temperature.