Aliphatic urethane polymers have been synthesized and characterized, using monomers with high molecular symmetry, to form amorphous networks with very uniform supermolecular structures, which can be used as photo-thermally actuable shape memory polymers (SMPs). The monomers used include hexamethylene diisocyanate (HDI), trimethylhexamethylenediamine (TMHDI), N,N,N',N'-tetrakis(hydroxypropyl)ethylenediamine (HPED), triethanolamine (TEA), and 1,3-butanediol (BD). The new polymers were characterized by solvent extraction, NMR, XPS, UV/VIS, DSC, DMTA, and tensile testing. The resulting polymers were found to be single phase amorphous networks with very high gel fraction, excellent optical clarity, and extremely sharp single glass transitions in the range of 34-153 degrees C. Thermomechanical testing of these materials confirms their excellent shape memory behavior, high recovery force, and low mechanical hysteresis (especially on multiple cycles), effectively behaving as ideal elastomers above T-g We believe these materials represent a new and potentially important class of SMPs, and should be especially useful in applications such as biomedical microdevices. (C) 2007 Wiley Periodicals, Inc.