Characterization and low temperature test of the flexibly crosslinked polyurethane copolymer by poly(dimethylsiloxane)

Shape memory polyurethane (SMPU) flexibly crosslinked by a hydrophobic poly(dimethylsiloxane) (PDMS) spacer at its side through allophanate bonding was tested for shape recovery at -30 degrees C and compared to a linear SMPU. The SMPU was composed of 4,4'-methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol) (PTMG), 1,4-butanediol (BD), and PDMS that was connected to SMPU chains by a second MDI. The mechanical and shape memory properties of two types of SMPU, differing in PTMG and PDMS content, were compared. In the best case, a 283% increase in maximum stress compared to the linear polymer was attained without any sacrifice of strain. Shape recovery at 45 degrees C increased to 91% and remained at more than 80% after four cyclic tests. Shape recovery at 0 degrees C could be improved by increasing PDMS content, and the critical shape recovery temperature decreased with increasing PDMS content. The PDMS-crosslinked SMPU demonstrated instant shape recovery at -30 degrees C in comparison with the linear SMPU that must be warmed to room temperature for complete shape recovery. The extraordinary shape memory results were analyzed and are discussed together with differential scanning calorimetry and infrared data.