Triple-shape properties of a thermoresponsive poly(ester urethane)

Thermo-mechanical investigations on a segmented poly(ester urethane) have shown that the material displays triple-shape functionality: gradual heating (-60\,^{\circ

}\mathrm {C} \to 23\,^{\circ }\mathrm {C} \to 60\,^{\circ }\mathrm

{C}) of programmed specimens leads first to the transformation from shape (A) to shape (B) and later from shape (B) back to permanent shape (C). In the essential two-step programming process, the first deformation state (B) is stabilized by crystallized soft segments at T<T_c, the second one (A) through the polymer's glassy state at T<T_g. The transition temperatures, as analyzed for the permanent-shaped polymer via DSC, are T_g≈-49 °C and T_m(onset)≈34 °C the material crystallizes when cooled at T_c(onset)≈4 °C. For the characterization of the material's cyclic thermo-mechanical triple-shape properties, maximum deformations of ɛ_m1 = 100% for shape (B) and ɛ_m2 = 130% for shape (A) were tested. In cycles N = 2-5 averaged shape fixing abilities of 74% (shape A, -60 °C), 109% (shape B, 23 °C) and shape recoverabilities of 103% (A \to B) and 96% (B \to C) could be detected. Values larger than 100% indicate the occurrence of plastic deformation during the second stretching.