To induce degradabilities in polymers in response to environmental conditions, end-modification reactions of poly(alpha-methylstyrene) (PMS) derivatives were carried out. 2-Phenylallyl halide derivatives such as 2-phenylallyl bromide, 2-(p-tolyl)allyl bromide, and alpha-trifluoromethylstyrene were found to be suitable end-modification agents. For example, the omega-2-phenylallyl-PMS derivative was prepared with almost quantitative functionality by the reaction of the living PMS derivative with 2-phenylallyl bromide. In a similar way, omega-3,3-difluoro-2-phenylallyl- and omega-2-(4-tolyl)allyl-PMS derivatives were synthesized. Based on thermogravimetric analysis, the 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-(p-tolyl)allyl-PMS. Actually, the onset temperature of omega-2-(p-tolyl)allyl-PMS derivatives was 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 depolymerization of the polymer at rather low temperatures. Therefore, it is concluded that a 2-phenylallyl substituent at the end of the PMS chain induces effective degradation through a radical mechanism.