New crosslinkable polymers with a nonlinear optical (NLO) active chromophore as a pendant group were synthesized by condensation chain polymerization via palladium-catalyzed carbon-carbon coupling reactions. The polymerization yields were almost quantitative between the diiodobenzene (DIB) and diethyldipropargyl malonate (DEDPM) or 4-(dimethylamino)-4 '-(6-dipropargylacetoxypropylsulfonyl)stilbene (DASS-6) monomers. To improve the molecular weight and mechanical properties of the NLO active polymer, we carried out the copolymerization with DIB and DASS-6 with various feed ratios of DEDPM. The resulting polymers were soluble in organic solvents and spun-cast onto indium tin oxide-coated glass substrates to make thin films. The molecular structures of the resulting polymers were characterized with various instrumental methods to confirm the carbon-carbon coupling reactions between the DIB and diacetylene monomers. The absorption of the ultraviolet-visible spectrum of the resulting polymers was drastically reduced after thermal curing at 160 degreesC because of the crosslinking of the reactive acetylene group in the polymer backbone. The electrooptic coefficient (r(33)) measured at 1.3 mum ranged from 7 to 15 pm/V.