In order to study the nature of interaction of arylbutadiynes with transient Gee radicals, polymerization and copolymerization of some vinyl monomers such as methyl methacrylate (MMA), styrene (ST), methacrylonitrile (MAN), vinylidene chloride (VCl2), ethyl acrylate (EA) and acrylonitrile (AN), were carried out in the presence of diphenylbutadiyne (DPB), 4,4＇-butadiynylene-N,N,N＇,N＇-tetra-n-butyl-dibenzamide (BBA), and 4,4＇-dibromodiphenylbutadiyne (BPB). MMA gave all intense ESR signal at the polymerization temperature when the polymerization system became viscous, and the number of radicals increased with polymerization time. Strong signals of polyEA and polyMAN radicals were also observed ill the presence of DPB when the polymerization system became almost solid. This is a unique case where active transient propagating radicals such as that of polyEA call be detected at polymerization temperature. The rates of polymerization decreased by the presence of the diacetylenes, but the molecular weights did not change with the diacetylene concentrations. UV spectroscopy revealed that there was no diacetylene unit bonded to the obtained polymers, indicating that degradative chain transfer is trot the case. The monomer reactivity ratios for MMA-ST and MMA-AN systems did not vary significantly in the presence of the diacetylenes, although some difference was observed. It seems that some arylbutadiynes interact with fi ee radicals but do not form bonds.