UV-curable polyurethane (PU) acrylates have been synthesized from polypropylene glycol (PPG), isophorone diisocyanate (IPDI), and three types of reactive diluents, i.e., 2-hydroxyethylacrylate (HEA), tripropyleneglycol diacrylate (TPGDA), and trimethylolpropane triacrylate (TMPTA). The effects of soft segment length, type, and concentration of reactive diluent on the mechanical and dynamic mechanical properties have been determined. When the soft segment length was short (750) tensile strength (sigma(b)) decreased, and elongation at break (epsilon(b)) generally increased with increasing HEA concentration, due respectively to the inferior strength of HEA homopolymer, and increased molecular weight between crosslinks (M(c)). Initial modulus (E) and ab increased and elongation at break (epsilon(b)) decreased with the increase of TPGDA concentration, and the effect was more pronounced as the soft segment length decreased. The hardness and sigma(b) increase with diluent concentration in PPG 2000-based materials was more pronounced with higher functionality diluent, due to the increased crosslinking density. The lower temperature glass transition peak of PU was not influenced by the TPGDA incorporation, whereas the higher temperature one moved toward still higher temperature. This was interpreted in terms of possible compatibility of hard segments and acrylates due to their similar polarity and hydrogen bonding.