Kinetics and mechanisms of catalyzed and noncatalyzed reactions of OH and NCO in acrylic polyol–1,6‐hexamethylene diisocyanate (HDI) polyurethanes. VI

Abstract Fourier transform infrared spectroscopy was used to study the kinetics of noncatalyzed and catalyzed polyurethanes. These studies show that for noncatalyzed acrylic polyol–hexamethylene diisocyanate (HDI) trimer reactions, the reactions between OH and NCO of HDI exhibit second‐order kinetics, with first‐order kinetics with respect to NCO and OH. On the other hand, when dibutyltin dilaurate (DBTDL) is used as a catalyst in acrylic polyol–HDI trimer reactions, the reaction rate is first order with respect to NCO and 0.5 order in OH and DBTDL concentrations. A mechanism for the catalyzed acrylic polyol–HDI trimer crosslinking reactions is proposed and it appears that an equilibrium involving associations between OH and DBTDL exists, resulting in the formation of an active anion, which interacts with NCO to generate polyurethanes. To further verify this mechanism, the influence of acidity on the reaction rate constant was investigated. When the acidity of the system is increased, retardation of urethane formation occurs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2322–2329, 2002