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Kinetics of glycidyl azide polymer-based urethane network formation



Reactions between hydroxyl-terminated glycidyl azide polymer (GAP) and different isocyanate curatives such as toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and methylene diicyclohexyl isocyanate (MDCI) at various temperatures viz. 30, 40, 50, and 60°C were followed by Fourier transform infra red spectroscopy. The reactions were found to follow second-order kinetics. With TDI and IPDI at 30°C, a two-stage reaction was observed. For GAP-TDI system, the second stage was slower than the first while for GAP-IPDI system, the second stage was faster than the first indicating dominance of autocatalytic effect. The stage separation occurred due to the difference in reactivity of the isocyanate groups and was found to narrow down with increase in temperature. The viscosity build up due to the curing reaction was followed for GAP-TDI system for comparison. The stage separation was evident in the viscosity build up also. Rheokinetic analysis done based on data generated showed a linear correlation between viscosity build up and fractional conversion. The kinetic and activation parameters evaluated from the data showed the relative difference in reactivity of the three diisocyanates with GAP. Both the approaches suggested that the reactivity of the isocyanates employed for the present study could be arranged as TDI > IPDI ≫ MDCI. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008