Viscoelastic properties of urethane and ester conjugation cardo polymers that contain fluorene group, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene (BPEF), were investigated. As for the urethane-type cardo polymers containing BPEF in the main chain, it had a high glass-transition temperature (T-g), which was observed as the a dispersion on viscoelastic measurement, and its temperature depended on the chemical structure of the spacing unit, such as toluene diisocyanate (TDI), 4,4'-methylene diphenyl diisocyanate (MDI), methylene dicycloexyl diisocyanate (CMDI), and hexamethylene diisocyanate (HDI). Moreover, the T-g of urethane-type cardo copolymers with various cardo contents increased with an increase of cardo content. Owing to the increase of T-g of cardo polymers, another molecular motion can be measured at the temperature between the alpha and beta dispersion that was assigned to the molecular motion of urethane conjugation unit around 200 K, and it was referred to as the alpha(sub) dispersion. The peak temperature of the alpha(sub) dispersion was influenced by the chemical structure of the spacing unit, but it did not change for the cardo polymer containing the same spacing unit. Consequently, it was deduced that the alpha(sub) dispersion was originated in the subsegmental molecular motions of the cardo polymers. Ester-type cardo polymer had higher T-g in comparison with noncardo polymer that consisted of dimethyl groups (BPEP) instead of BPEF as well. The alpha(sub) dispersion was also measured at the temperature between the alpha and beta dispersion, which was assigned to the molecular motion of ester conjugation unit, around 220 K. For ester cardo polymer, the gamma dispersion was measured in a low-temperature region around 140 K, and it was due to a small unit motion in the ester-type cardo polymers, such as ethoxyl unit, -C2H4O-Moreover, the intensity of the y dispersion of noncardo polymer was higher than that of cardo polymer, which means the molecular motion was much restricted by the cardo structure of BPEF. (c) 2005 Wiley Periodicals, Inc.