For the first time the flexible cyclopentyl ring is used to build mesogenic units, and thus a novel mesogen-jacketed liquid crystalline polymer (MJLCP) poly(dicyclopentyl vinylterephthalate) is synthesized. The polymer forms a stable mesophase which changes to an isotropic phase at 267 degrees C. The formation of a stable mesophase may be attributed to the spatial interaction among flexible side groups which converts them into rigid mesogenic units.