Kinetics of castor oil based polyol-toluene diisocyanate reactions

The kinetic aspects of the polymerization reactions of castor oil (C.O.) and two polyurethane prepolymers based on it (R60 and R92), differing in their hydroxyl number, with toluene diisocyanate (TDI) has been analyzed. The polymerization kinetics were studied under isothermal conditions using different amounts of dibutyl tin dilaurate (DBTDL) as a catalyst. The kinetics of the catalyzed reaction are described by only single order equations while the kinetics of uncatalyzed reactions were described by two independent second order equations giving the reactions of ortho and para-NCO groups. The isocyanate group in the ii-position shows two to three fold higher reactivity than that in the 2-position. The values of rate constants for prepolymers at 30 degrees C were; three times more (k(1) = 4.5 x 10(-4)) than that of C.O. (k(1) = 1.4 x 10(-4)). The activation energies were found to be less (greater than or equal to 6 kJ/mol) in prepolymers compared to C.O. indicating higher reactivities of the former, both in uncatalyzed and catalyzed systems. (C) 1998 Elsevier Science Ltd. All rights reserved.