Effects of isocyanate addition on viscosity of ester-based polyurethanes

Polyurethane (PU) is widely used in high performance adhesives, where viscosity and curing trends are very important. Bonab and others described PU viscosity changes during polymerization.They argued that due to competing effects of heat transfer, which tends to lower viscosity, and polymerization reaction, which tends to increase viscosity, in the first stage, viscosity is constant or it can slightly drop. In this work viscosity changes during polymerization were investigated as well as NCO groups changes during the polymerization between industrially widespread isocyanate and polyols.