Abstract
Miscibility and thermomechanical properties of blends of polyurethane(PU) with either polycarbonate(PC) or polyacrylonitrile(PAN) were investigated in order to understand the shape memory characteristics of PU blends. The miscibility of blends was analyzed in terms of melting temperature depression and change in glass transition temperature(Tg). PU/PAN blends showed an existence of miscibility between PAN molecules and hard segments of PU, whereas no evidence for miscibility was shown between PAN molecules and soft segments of PU. However, it was found that PC molecules in PU/PC blends had some miscibility with both hard and soft segments of PU. Percent shape memory of PU/PC and PU/PAN blends, which was obtained from respectively. Percent shape fixity of blends increased with increasing PC and PAN contents in blends. The difference in shape momory and shape fixity between PU/PC and PU/PAN blends was not so large. However, judging from the relationship between shape memory and modulus ratio of blends, it was considered that shape recovery effect of PU/PC blend was larger than that of PU/PAN blend. The modulus ratio was defined as a ratio of tensile modulus measured at temperature of Tg-20($^{\circ}C$) to that at temperature of Tg+20($^{\circ}C$). Such a difference in thermomechanical property between two blends was likely to result from a difference in the miscibility of blends. That is, PU/PC blend formed uniformly continuous PU phases, whereas PU/PAN blend did not.
