Thermal molecular motion of a series of comb-shaped polymers with heptadecafluorodecyl side chains (C(F)8C2-) has been studied based on dynamic viscoelastic measurement. The main chain of comb-shaped polymers was poly(fumarate), poly(methacrylate), and poly(acrylate). Poly(fluoroalkylfumarate) with heptadecafluorodecyl group, P(CF8C2-IPF) was amorphous polymer, whereas poly(acrylate) and -poly(methacrylate) with C(F)8C2-, P(CF8C2-Acr) and P(CF8C2-MAcr) showed mesomorphic behavior. The pervaporation behavior of water/organic mixtures through amorphous polymer, P(CF8C2-IPF), and mesomorphic one, P(CF8C2-Acr), were investigated. The distinct increase in permselectivity has been observed at the mesomorphic transition of P(CF8C2-Acr).