Poly(phenylenevinylene)s as Sensitizers for Visible Light Induced Cationic Polymerization

Abstract

A novel visible light sensitive photoinitiating system for the cationic polymerization of oxiranes such as cyclohexene oxide (CHO) and vinly monomers such as isobutyl vinylether (IBVE) and N -vinyl carbazole (NVC) using poly(phenylenevinylene) (PPV) derivatives as photosensitizers is described. The cationic polymerization of these monomers was initiated at room temperature upon irradiation in the visible region (λ inc > 400 nm) in bulk or methylene chloride solutions with poly(phenylenevinylene)- g -polystyrene (PPV- g -PSt) or poly(phenylenevinylene)- g -poly(ε-caprolactone) (PPV- g -PCL), in the presence of oxidizing salts such as diphenyliodonium hexafluorophosphate (DPI), and N -ethoxy-2-methylpyridinium (EMP). The initiation mechanism, based on the optical absorption measurements, free energy changes (Δ G ), and proton scavenging studies, involves formation of exciplex by the absorption of light in the first step. Subsequently, an electron transfer from the excited PPV- g -PSt or PPV- g -PCL to oxidizing salt occurs to yield radical cations of the PPV backbone. Thus, formed radical cations abstract hydrogen from the surrounding monomer or the solvent to release a Bronsted acid, which initiates the polymerization. Triphenylsulphonium hexafluoroarsenate (TPS) was found to be inefficient in the photoinduced electron transfer process due to the unfavorable thermodynamic conditions.