Polyurethane ionomers having shape memory effects

Polyurethane (PU) ionomers and non-ionomers with various soft segment contents (SSC) and lengths have been synthesized from polycaprolactone diols (PCL), 4,4'-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD) and dimethylolpropionic acid (DMPA), and tested for shape memory behaviour as well as for mechanical and dynamic mechanical properties. It was found that ionomers gave higher hardness, modulus and strength as compared with non-ionomers, and the effects were more pronounced with increasing hard segment contents (HSC) and at room temperature, since the increased HSC makes use of more Coulombic forces which are stronger at room temperature than at high temperature. Regarding the tensile cyclic behaviour, ionomers gave higher recovery strain and lower residual strain, and these were interpreted in terms of dynamic mechanical properties. i.e. the higher the rubbery modulus, the higher the recovery strain results. (C) 1998 Elsevier Science Ltd. All rights reserved.