As a fundamental study for chemical recycle of waste vulcanized rubber to reproduce functional polymers, polyisoprene (PI) was thermally fragmented to obtain low molecular weight PI in the presence of thiophenol (PhSH). PI (M-w = 51,000) was heated at 140 degrees C under air atmosphere to give low molecular weight PI. The fragmentation in the presence of PhSH effectively decreased the molecular weight (M-w = 7400), which is significantly lower than that in the fragmentation in the absence of PhSH. The fragmented PI contained phenyl sulfide moieties based on the addition of phenyl thiyl radical to the hydrogen abstracted methylene or the double bond moieties. T(g)s of the fragmented polymers were higher than that of the original PI, despite the lower molecular weights, probably because of the introduction of the rigid phenyl sulfide moieties and the terminal polar carbonyl groups formed by oxidation. (c) 2007 Wiley Periodicals, Inc.