The end-modification reactions of poly(alpha-methylstyrene) (PMS) derivatives were examined as a means of inducing degradabilities in polymers in response to environmental conditions. When diphenylphosphine chloride was used as a modifier for the living end of para-substituted PMS, the coupling efficiency was similar to 50%. 2-Phenylallyl halide derivatives such as 2-phenylallyl bromide, 2-(4-tolyl)allyl bromide and alpha-trifluoromethylstyrene were found to be suitable end-modification agents. For example, omega-2-phenylallyl PMS was prepared with almost quantitative functionality by the reaction of the living PMS with 2-phenylallyl bromide. In a similar way, omega-3,3-difluoro-2-phenylallyl and omega-2-(4-tolyl)allyl PMS derivatives were synthesized. On the basis of thermogravimetric analysis, onset of the degradation temperature of the end-modified PMS derivatives decreased in the following order : omega-hydrogen- > omega-3,3-difluoro-2-phenylallyl- > omega-2-phenylallyl- > omega-2-(4-tolyl)allyl-PMS. The onset temperature of omega-2-(4-tolyl)allyl-PMS derivatives was in fact 50 degrees C lower than that of omega-H-PMS derivatives. These results indicate that the active species is produced effectively at the end unsaturated bond, which initiates the depolymerization of the polymer at fairly low temperatures. Ionic degradation of these polymers was also investigated using butyllithium as an anionic initiator and methanesulfonic acid as a cationic initiator. Tendencies similar to the thermal degradation were observed. Therefore, it is concluded that a 2-phenylallyl substituent at the end of the PMS chain induces effective degradation through several mechanisms such as radical, anionic and cationic depolymerization reactions.