A three-arm star azo side-chain liquid crystalline (LC) homopolymer, poly[6-(4-methoxy-4-oxy-azobenzene) hexyl methacrylate] (PMMAZO), was synthesized by atom transfer radical polymerization (ATRP) method. The polymerization of 6-(4-methoxy-4-oxy-azobenzene) hexyl methacrylate proceeded in a controlled/"living" way. A series of three-arm star LC block copolymers (PMMAZO-b-PMMA) were also synthesized. The polymers were characterized by H-1 NMR, gel permeation chromatograph, and UV-vis spectra, respectively. The both polymers of PMMAZO and copolymers of PMMAZO-b-PMMA exhibited a smetic phase and a nematic phase. As concern to the PMMAZO, the glass-transition temperature (T-g) and phase-transition temperature from the smetic to nematic phase and from the nematic to isotropic phase increased with the increase of molecular weight (Mn-(GPC)) of PMMAZO. The phase transition temperature of the block copolymers, PMMAZO-b-PMMA, with the same PMMA, block was similar to that of PMMAZO. However, the T-g of the PMMAZO-b-PMMA decreased at low azo content and then increased with the increasing Mn(GPC) when azo content was above 61.3%. With illumination of linearly polarized Kr+ laser beam at modest intensities (35 mW/cm(2)), Significant surface relief gratings formed on PMMAZO films with different molecular weights were observed. (C) 2007 Wiley Periodicals, Inc.