We have synthesized the AB type diblock copolymer with polystyrene and poly(6-[4-(4'-methoxyphenyl)phenoxy]hexyl methacryrate) by sequential anionic living polymerization. The copolymers were prepared with quantitative yields, possessing the predictable M-n values, compositions and narrow molecular weight distributions. The thermotropic phase behavior and structures were examined for six copolymers with the weight fraction of LC segments from 24wt% to 45wt%. All copolymers exhibit the crystal-SmA and the SmA-isotropic phase transitions. Microphase separations were examined as a function of the weight fraction of two segments and in a relation with the micro structure of LC segment.