New catalysts for urea formation reaction. I. Effect of catalyst on molecular weight of polyureaurethane and determination of the minimum demolding time

Abstract

Synopsis2-Methyl benzoic acid as a new catalyst for urea formation reaction has a significant effect on the molecular structure of polyureaurethane. For instance, it increased molecular weight of polyureaurethane, hut decreased chemical crosslink density. The minimum demolding time (DT) of polyureaurethane as an index of catalytic activity was also discussed based on the mechanical properties. DT is defined as the torque time for a mixture of curative and prepolymer to reach 90% of its nearly final value. A marked increase in extension ratio a t break ( E B ) before DT was partially attributed to intermolecular entanglements which arose a t molecular weights higher than 4500 [rheological critical molecular weight of poly(oxytetramethylene)glycol]. Primary aliphatic amines in amide solvents selectively cleaved hiuret or allophanate bonds of polyureaurethane. This helped to determine molecular weight of crosslinked polyureaurethane.