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Kinetic Aspects of Chain Extension Reaction Using Water-Soluble Diamines in Aqueous Polyurethane Dispersion

ABSTRACT Chain extension reaction using water-soluble chain extenders was investigated with varying carbon number of the chain extenders (ethylene diamine, diaminobutane, and 1,6-hexane diamine) and their feed rates in the preparation of polyurethane dispersions using prepolymer method. The chain extension reaction between residual NCO groups from aliphatic diisocyanate (isophorone diisocyanate) and water-soluble diamines was observed by monitoring pH of the aqueous phase. A separate swelling experiment using these water-soluble diamines was conducted to investigate the locus of chain extension reaction and chain extension model based on the experimental results was suggested. Apparent reaction rate obtained by pulse-relaxation and the time-evolution average particle size were strongly dependent on the chain length of the diamines as well as feed rate of the chain extender. Moreover, the tensile strength and elongation of the thin films cast from these polyurethane dispersions were also influenced by the chain length.