Abstract: The bulk steppolymerizations among 4,4′/2,4′diphenylmethane diisocyanate, polytetramethylene ether glycol, and 1,4butylene glycol were carried out in a torque rheometer, in the presence of a Bi/Zn composite catalyst or catalystfree, leading to a thermoplastic polyurethane (TPU). The mean molecular weights of TPU sampled during synthesis process were measured using gel permeation chromatography, and were correlated with the reaction rate constant, time, and catalyst concentration. The change tendency of molecular weight of TPU with time was well simulated and explained.

Key words: diphenylmethane diisocyanate, polytetramethylene ether glycol, thermoplastic polyurethane, weight average molecular weight