This paper reports a novel and practical method for the synthesis of styrene-isoprene-derived cycloolefin copolymer analogues via the intramolecular Friedel-Crafts alkylation of well-defined random copolymers of styrene and isoprene prepared by living anionic copolymerization in the presence of a small amount of tetrahydrofuran as a randomizer. The random copolymers with an almost equimolar amount of the two monomers (styrene: isoprene = 48:52) and a predominant 1,4-isoprene-enchainment (1,4-:1,2-:3,4- = 67:1:32) were intramolecularly cyclized with CF3SO3H efficiently to give the soluble cycloolefin copolymer analogues with a high glass transition temperature (T-g). The T-g increased dramatically (T-g = 20 vs 130 degrees C) on cyclization between the aromatic ring of the styrene unit and the adjacent C=C bond in the isoprene unit via the intramolecular Friedel-Crafts alkylation that results in the tetrahydronaphtyl bicyclic unit in the backbone chain, for which the highest T-g was observed at the equimolar content of isoprene and styrene. The predominant Friedel-Crafts cyclization between the styrene and the adjacent isoprene units was supported by the model reactions of the corresponding low molecular weight model compounds.