Polymers degradable under environmental conditions through end‐modification of poly(α‐methylstyrene) derivatives

Abstract

To induce degradabilities in polymers in response to environmental conditions, the end‐modification reactions of poly(α‐methylstyrene) derivatives were carried out. When diphenylphosphine chloride was used as a modifier for the living end of para‐substituted PMS, the coupling efficiency was ca. 50%. 2‐Phenylallyl halide derivatives such as 2‐phenylallyl bromide, 2‐(4‐tolyl)allyl bromide, and α‐trifluoromethylstyrene were found to be suitable end‐modification agents. For example, ω‐2‐phenylallyl PMS was prepared with almost quantitative functionality by the reaction of the living PMS with 2‐phenylallyl bromide. In a similar way, ω‐3,3‐difluoro‐2‐phenylallyl and ω‐2‐(4‐tolyl)allyl PMS derivatives were synthesized. Based on thermogravimetric analysis, onset of the degradation temperature of the end‐modified PMS derivatives decreased in the following order: ω‐hydrogen‐ > ω‐3,3‐difluoro‐2‐phenylallyl‐ > ω‐2‐phenylallyl‐ > ω‐2‐(4‐tolyl)allyl‐PMS. Actually, the onset temperature of ω‐2‐(4‐tolyl)allyl‐PMS derivatives was 50°C lower than that of ω‐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 rather 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.