A conjugated alternating copolymer, poly[bicarbazolylene-alt-phenylenebis(eyanovinylene)] (named PCPV), was prepared via the Knoevenagel condensation in the presence of tetrabutylammonium hydroxide. Tetrahydrofuran-soluble low molecular weight materials and insoluble polymer were obtained. The two fractions were characterized in detail by ESR and solid and solution NMR spectroscopies. Strong ESR signals were observed from the pristine PCPV polymer in both fractions. This was explained by the rotational cleavage of the cis vinylic bond to produce two r radicals, called biradicals, which diffuse along the main chains to form radical cations stabilized by conjugation in the alternating repeating moieties. In particular, the insoluble fraction shows an extremely strong and sharp line width signal with a spin concentration equal to 5.8 x 10(17) spins/g. The alternating copolymer synthesized can be considered as a novel conjugated material analogous to substituted polyacetylenes with respect to the mobile unpaired electrons. The solid NMR spectrum of the insoluble fraction of the PCPV copolymer is reported for the first time. By comparison with solution NMR studies of the soluble fraction and of a model compound of the repeating unit, the structure of the copolymer was established. The H-1 NMR spectrum of the soluble fraction allowed calculation of the DPn whose values roughly agree with that estimated by SEC measurements. However, the NMR signals of the soluble fraction were somewhat broadened because of the presence of unpaired electrons in the main chains.