Bulk polymerizations of 4

4'/2

4'-diphenylmethane diisocyanate/polytetramethylene ether glycol/1

4-butylene glycol without and with the addition of Bi/Zn composite catalyst were carried out to synthesize thermoplastic polyurethane (TPU) in a torque rheometry to simulate twin-screw extruder conditions

and the rheokinetics of polymerization process was investigated.The relations between torque and weight average molecular weight (MW) of TPU were corrected based on two-dimensional flow simplification

correction between melt viscosity and molecular weight

and Arrhenius equation.The rheokinetics model was used to fit the variation of MW of TPU during polymerization.The fitted MW of TPU showed good agreement with that determined by gel permeation chromatography.The rheokinetic model could quickly provide real-time fitting results of MW of TPU from the torque for the whole synthesis process.