We observed the spontaneous shape change of a uniaxially oriented liquid-crystalline elastomer composed of smectic main-chain liquid-crystalline polyesters in a cyclic heating-cooling process. Although the elastomer contracted by about 650% on heating up to the isotropic phase, the sample length recovered by about 450% on cooling to room temperature in the first heating-cooling process. In contrast, the elastomer exhibited completely reversible deformation in the second heating-cooling process. The shape change occurred with almost no change in the orientational order of mesogens in the temperature region of the liquid-crystalline phase. The mechanism of the spontaneous thermotropic shape change is discussed.
