Depolymerization kinetics for thermoplastic polyurethane elastomer degradation in subcritical methanol

The depolymerisation kinetics of thermoplastic polyurethane elastomer (TPU) in subcritical methanol was investigated. The molecular weight distributions (MWDs) of the samples were measured with gel permeation chromatography (GPC) and analysed through Origin 8.5 peak fit module, and continuous distribution kinetics was employed to describe the degradation procedure. Experimental and modelling results indicated that the degradation procedure was two stage owing to the existence of weak linkages between soft and hard domains. During degradation, weak linkages primarily completed the fracture, and strong linkages underwent scission throughout the process. The fracture of TPU chain involved random and chain-end scissions. With continuous distribution kinetics, random scission was divided into two stages by the time when weak linkages were totally disrupted. The activation energies in stages 1 and 2 were 181 and 241 kJ/mol. Chain-end scission was only related to strong linkages. The activation energies of the three kinds of monomers---4,4′-methylene diphenyl carbamate (MDC), 1,4-butanediol (BDO) and dimethyl adipate (DMA) were 137.0, 122.5 and 224.9 kJ/mol, respectively.