Effect of the hydrogen bonding on the inelasticity of thermoplastic polyurethane elastomers

The effect of hydrogen bonding on the cycling tensile responses of thermoplastic polyurethane elastomers (TPUs) was followed. Hydrogen substitution was carried out by replacing the usual fully hydrogenated forms of the diol chain extender diethylene glycol (DEGh) or of the macrodiol polytetrahydrofurane (PTHFh) with their fully deuterated analogues DEGd and PTHFd. The TPUs segmental orientation was followed by means of infrared dichroic measurements. The hard segment (crystallizing or not) was varied by inclusion of a conventional rigid diisocyanate, 4,4′-diphenyl methane diisocyanate (MDI) and of an isocyanate with a large conformational mobility 4,4′-dibenzyl diisocyanate (DBDI). Inelastic effects were most pronounced when the hard segment crystallized. Irrespective of the isotopic forms of the chain extender and macrodiol used in the material synthesis, the residual strain and hysteresis energy dissipation were highest for hard segments of DBDI than of MDI. While the TPUs derived from DEGd were more resilient than the similar polymers obtained with the DEGh, there were no significant differences between the resilience of the TPUs achieved with the PTHFh and PTHFd. A quantitative correlation was found between the magnitude of the Mullins effect and the fractional energy dissipation by hysteresis under cyclic straining, giving a common relation that was approached by all the materials studied. The results provide new perspectives into the physical origin of inelastic effects in reinforced elastomers.