Effects of the Reaction Temperature on the Concentration of Allophanaie Linkages in the Polyurethane Formation

Abstract

In the reaction of bis(4-isocyanatophenyl)methane (BIM) with a diol mixture of poly(ethylene adipate) (Mn=2000) and ethylene glycol (molar ratio=1: 2; NCO/OH molar ratio=1.00)in bulk and in N, N-dimethylformamide (DMF), the effects of reaction temperature on the concentration of allophanate linkages in resulting polyurethanes were studied. When the reaction temperature of polyurethane formation in bulk was higher than 120 °C, increase in the reaction temperature results in decrease in the concentration of allophanate linkages. This phenomenon was explained by that the degradation of allophanate linkages was predominantly proceeded rather than their formation when the reaction temperature is higher. On the other hand, when the reaction temperature of polyurethane formation in DMF was higher than 100 °C, the polyurethane with high molecular weight was not formed because the reaction of BIM with DMF results in the deviation of NCO/OH molar ratio from 1.00. Therefore increase in the reaction temperature of polyurethane formation in DMF was inapplicable to decrease in the concentration of allophanate linkages.