Introduction Singlet oxygen I0^(IA ) is a reactive intermediate in the sensitized photoo~idat~on of several polymers (CARLSSON and WILES,1974,1976; RABEK and RANBY,1975,1978; R~NBY and Rabek,1978),especially polydienes (GOLUB et a1,1977,1978; NG and GUILLET,1978; RABEK and RANBY,1976,1979a,1979b). It is of commercial interest to determine its role in the deterioration of polymeric materials and to find new effective singlet oxygen q~enchers. Various compounds have been reported to quench "0 o including carotenoids (BELLUS,1978; GARNER and WILLIAMS,1~78; F00TE et ai,1970), amines (BELLUS,1978, QUANNES and WILSON, 1968) and transition metal chelates (CARLSSON et a1,1972,1974; FLOOD et a1,1973; ZWEIG and HENBERS0N,1975). This paper presents results of stabilization against the oxidation of cis-1,4-polybutadiene by a new type of singlet oxygen quencher, 4-(1-imidazolyl)-phenol. Experimental A commercial sample of cis-1,4-polybutadiene (PB) (Ameripol CB200 from Goodrich Chemical Co.) was purified by dissolving in benzene (analytically pure grade) and precipitating with ethanol (spectral grade) in nitrogen atmosphere. This procedure was repeated twice. 4-(1-imidazolyl)-phenol (IP)(Ega-Chemi,Germany)(chemioally pure) was recrystallized twice from n-hexane. Quenching experiments were performed with rubrene I~10,11,12-tetra-phenylnaphtacene)(Ega-Chemi,Germany) as the receptor. Bleaching of rubrene (RU) absorption at 520 nm was used to follow the rubren~ oxidation to endo peroxide. Using visible light (460nm), 0_ was generated inca solution of benzene and methanol (9:1).M~thylene blue (10-PM) was used as photosensitizer(RABEK and RANBY,1976,1979a,1979b). The stabilization effect of IP for the UV(254 nm) photodegradation of PB in benzene solution (I wt-%) was measured by determining the amount of chain scission (S). This chain scission,where S = (M /M .-1),was estimated from viscometric O measurements of 1,4-P~ solution in benzene at 32~ using an Ubbelhode viscometer. The effects of IP were compared with those of 2,6-di-tert-butyl-p-cresol (DTBC)(Ega-Chemi,Germany) which is an active free radical scavenger. The stabilization