A new class of liquid-crystalline (LC) homopolymers of poly{11-[4-(3-ethoxycarbonyl-coumarin-7-oxy)-carbonylphenyloxy]-undecyl methacrylate} containing a coumarin moiety as a photocrosslinkable unit with various polymerization degrees and their LC-coil diblock and LC-coil-LC triblock copolymers with polystyrene as the coil segment was synthesized with the atom transfer radical polymerization method. All the homopolymers and block copolymers synthesized here exhibited narrow polydispersities, indicating well-controlled living polymerization. Differential scanning calorimetry, polarized optical microscopy, and wide-angle X-ray diffraction confirmed that all the homopolymers and block copolymers exhibit a monolayer smectic A phase. Coumarin moieties in the polymers can be photodimerized under lambda > 300 nm light irradiation to yield crosslinked network structures, which improve the thermal stability of a polymer nanostructure because of microphase separation. (C) 2003 Wiley Periodicals, Inc.