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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 °C, regenerating TDI and blocking agent 4-bromopyrazole. At 238 °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 °C, indicating generally hydrophilic natures of samples. DSC thermogram indicates the presence of glass transition temperature of synthesized polyurethanes at − 30 to − 40 °C. Viscosity measurements of polyurethanes in chloroform at different temperatures indicated decrease in viscosity at higher temperature. [ABSTRACT FROM AUTHOR]

Hexamethylene diisocyanate (HMDI) reacts with 4-bromo-1H-pyrazole as a blocking agent to form blocked adducts of isocyanates. The adducts were characterized by FTIR, NMR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). In the FTIR spectra, disappearance of a peak at 2250–2270 cm−1 is the indication of blocking of diisocyanate molecule with 4-bromo-1H-pyrazole blocking agent. The DSC thermogram shows that at 185 °C, the blocked adduct de-blocks and HMDI and blocking agent 4-bromo-1H-pyrazole has been regenerated. At 185 °C, regenerated HMDI reacts with polyols of different molecular weights to form polyurethane. The polyurethanes were characterized by FTIR, NMR, DSC, TGA and contact angle measurements. These are useful for hydrophilic coating. [ABSTRACT FROM AUTHOR]

Diisocyanates, particularly toluene diisocyanate (TDI), are useful for the preparation of various polyurethanes with specific applications as leather-like materials, adhesives and insoles, etc. Blocking agents can be used for the operational simplicity and to reduce the hazards of TDI. In this paper, we reported the use of 3-(4-bromo-phenyl)-1H-pyrazole to block toluene diisocyanate (TDI). FTIR, NMR, thermogravimetric analysis, contact angle analysis and differential scanning calorimetry (DSC) were used for the characterization. The effectiveness of the blocking was confirmed by spectroscopic techniques. The DSC thermogram showed that blocked adducts deblock at 240 °C, causing the regeneration of TDI, and causing the diisocyanates to react with polyols of different molecular weights, forming polyurethanes. The characterization of the polyurethanes was performed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and a contact angle study. [ABSTRACT FROM AUTHOR]