Structure–property relationships in thermoplastic elastomers. IV. Dynamic mechanical relaxations in polydioxolane,polybutyltrioxocane, and poly(propylene oxide) polyurethanes

Dynamic mechanical measurements had been made on polyurethanes of a range of hard segment content (HSC) obtained from α,ω-dihydroxy derivatives of polydioxolane, polybutyltrioxocane, and poly(propylene oxide) of 2000–12,000 MW coupled with MDI and TDI with hydroxyethyl phthalamide chain extenders. N-methylated chain extender was used to investigate the effect of hydrogen bonding. A broad γ transition was observed between −100 and −115°C attributable to the local motion of methylene sequences with a distribution of relaxations. The β-transition between −55 and −72°C is influenced by the degree of hydration; the α-transition occurs at nearly the same temperatures for all the TPEs, independent of HSC and thermal history. The magnitude of the loss tangent peak is nearly proportional to the soft segment content; the peak corresponds to the glass transition. An α-transition at higher temperature is sensitive to the structure of soft segment, HSC, and thermal history. It is probably associated with the melting of some weakly ordered regions in the soft domain. The hard domain counterpart was observed at the next higher temperature as the ϵ-relaxation. The final large loss of storage modulus occurs at temperatures much below the melting transition.