Non-Gaussian behavior of self-assembled thermoplastic polyurethane elastomers synthesized using two-step polymerization and investigated using constant-strain stress relaxation and molecular modeling techniques

Self-assembly thermoplastic polyurethane elastomers were synthesized using two step polymerization process. FTIR spectroscopy confirmed the formation of 2D-hydrogen bonding network across neighboring chains and the self-assembly of the hard block sequences as evident by the presence of a sharp peak at 1710 cm−1 corresponding to the hydrogen-bonded urethane groups. Stress–strain data of the synthesized samples revealed a non-Gaussian pattern at higher extents of elongation as the moduli of the samples showed upturns at high strain values of 200% the original length. To our knowledge, this is the first time this result has been reported for segmented polyurethane elastomers and is attributed to the increase in the excluded volume of the hard blocks leading to higher ordering patterns at higher elongations. Molecular modeling study indicated that the anomalous behavior is attributed to the significant loss in the entropy showing much lower values for the self-diffusion coefficients of the self-assembly hard blocks due to the restriction in their mobility. NMR and TGA were also done to confirm the molecular structures and the response of the synthesized samples to thermal decomposition, respectively, which showed 60 °C increment in the decomposition temperature with the increase in the self-assembly hard block sequences.