Effects of the Pendant Naphthalene Group on the Mechanical Properties and Low Temperature Shape Memory Effect of Polyurethane Copolymer

A series of shape memory polyurethane (SMPU) attached by pendant naphthalenes along the polyurethane (PU) chains was prepared. The SMPU chain was composed of 4,4'-methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol)-2000, 1,4-butanediol (BD) as a chain extender, and glycerol. The naphthalene was connected to the glycerol moiety of the PU chain using the second MDI as a connecting agent. The key point was whether the pendant naphthalene would improve the mechanical properties and shape recovery at subzero temperature. Similar mechanical properties (maximum stress and strain at break) and shape recovery, compared to the previous SMPUs, were attained at temperature above T _m , but a contrasting difference was observed in the shape recovery at subzero temperature. The conventional SMPU was not able to return to the original shape below -10°C, but the developed SMPU recovered its original shape even at -30°C. The reason for the exceptional shape recovery at both low temperature and ambient temperature is sought from a structural viewpoint.