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6210854 
Journal Article 
Kinetics of the molar mass decrease in a polyurethane melt: a rheological study 
Hentschel, T; Munstedt, H 
2001 
1 
Polymer
ISSN: 0032-3861 
Elsevier 
42 
7 
3195-3203 
WOS:000166636400047 
Dynamic melt viscometry was used to study the kinetics of molar mass decrease in the molten liquid state of a polyurethane elastomer based on 4,4′-diphenyl-methane diisocyanate and 1,4-butanediol. It was found that at constant temperatures chosen between 180 and 220°C the molar mass of the polyurethane melt decreased continuously until a thermal equilibrium was reached. The rates as well as the degree of decrease strongly depend on temperature and time. Based on a kinetic model, the temperature dependence of the zero shear viscosity was shown to be controlled not only by the molecular mobility but also by the change in molar mass. The true activation energy of flow (131kJ/mol) could be calculated after separation of the molar mass contribution. The rate constants and the activation energies of urethane formation and dissociation were also determined. 
thermoplastic polyurethane elastomers; molar mass decrease; dissociation kinetics