UNPERTURBED DIMENSIONS OF IRREGULAR POLY(PHENYLACETYLENE) Dana Rédrová 1 , Jan Sedláček 1 , Majda Žigon 2 , Jiří Vohlídal 1 1 Department of Physical and Macromolecular Chemistry, Laboratory of Specialty Polymers, Faculty of Science, Charles University, Albertov 2030, CZ-128 40, Prague 2, Czech Republic 2 National Institute of Chemistry, Hajdrihova 19, SI-1000, Ljubljana, Slovenia Dilute solution characteristics of irregular (ca 30 % trans) poly(phenylacetylene), PPA, were determined by using the SEC/RI/MALS technique in order to obtain a deeper insight into discrepancy between presumed rigidity of conjugated polyvinylene molecules and their apparent flexibility resulting from earlier viscometric measurements. PPA was found to exhibit molecular-weight dependence of the radius of gyration (known as the scaling law) in tetrahydrofurane solutions similar to that of irregular polystyrene (saturated analogue of PPA), and also unperturbed dimensions of these polymers were found to be almost equal. This rather surprising observation is explained as a result of the compensation of the effect of segments´ stiffening due to conjugation by significant π-π attraction between highly polarizable PPA segments with well-delocalized π-electrons. More detailed analysis of the obtained results could not be done since the mean-square end-to-end distance of polyvinylene chains yet has not been calculated and comparable data on other polyvinylenes are not available. Keywords. polyacetylenes, polyvinylenes, unperturbed dimensions, radius of gyration, polyphenylacetylenes Received Accepted 1