Rheo-kinetic evaluation on the formation of urethane networks based on hydroxyl-terminated polybutadiene

Rheo-kinetic studies on bulk polymerization reaction between hydroxyl-termi nated polybutadiene (HTPB) and di-isocyanates such as toluene-di-isocyanate (TDI), hexamethylene-di-isocyanate (HMDI), and isophorone-di-isocyanate (I PDI) were undertaken by following the buildup of viscosity of the reaction mixture during the cure reaction. Rheo-kinetic plots were obtained by plott ing In (viscosity) vs. time. The cure reaction was found to proceed in two stages with TDI and IPDI, and in a single stage with HMDI. The rate constan ts for the two stages k(1) and k(2) were determined from the rheo-kinetic p lots. The rate constants in both the stages were found to increase with cat alyst concentration and decrease with NCO/OH equivalent ratio (r-value). Th e ratio between the rate constants, k(1)/k(2) also increased with catalyst concentration and r-value. The extent of cure reaction at the point of stag e separation (x(i)) increased with catalyst concentration and r-value. Incr ease in temperature caused merger of stages. Arrhenus parameters for the un catalyzed HTPB-isocyanate reactions were evaluated. (C) 2001 John Wiley & S ons, Inc.