Photo and Radiation Induced Ionic Polymerization

Photo-induced cationic polymerizations of styrene and x-methylstyrene, which are weak electron donors and contain no hetero atom, were carried out in the presence of electron acceptors such as tetracyanobenzene and pyromellitic dianhydride to elucidate the polymerization mechanism initiated through an excited charge transfer interaction. Cyclohexene oxide was also polymerized by photo-illumination in the presence of these electron acceptors. The mechanism of this ring-opening polymerization was thought to be a cationic one. Photo-polymerization of nitroethylene in tetrahydrofuran was carried out with the purpose of extending this process to anionic systems. The results obtained have been compared with the cases of ionic polymerizations by ionizing radiation and conventional catalysts. It has been found that the radiation induced polymerization of styrene is considerably enhanced by the use of an extremely rigorous drying technique" 2 Evidence that this polymerization is due mainly to a cationic propagation, comes both from scavenger studies and from the determination of reactivity ratios in copolymerization experiments with c-methylstyrene and isobutyl vinyl ether. The large k value (>3 x 106 M 1 sec 1) is explained as a characteristic ion—dipole reaction for the free ionic propagation process3' . On the other hand, photo-induced ionic polymerization of styrene and c-methylstyrene which are weak donors and contain no hetero atom, were carried out in the presence of tetracyanobenzene and pyromellitic dianhydride to elucidate the polymerization mechanism initiated through an excited charge transfer interaction5. Photo-illumination was carried out with a high pressure mercury lamp through filters which cut off wavelengths shorter than 300 nm. The photoinduced polymerizations of these monomers were observed in 1 ,2-dichloroethane and methylene chloride in the presence of electron acceptors as shown in Table 1. The degree of polymerization of the poly(cx-methylstyrene) formed at —30°C was estimated to be 660 by viscometry. No polymer was obtained in the dark, in the absence of acceptors or without rigorous drying of monomer and solvent. This polymerization was completely inhibited by the addition of a trace amount of proton scavenger such as triethylamine as reported for the radiation-induced ionic polymerization. This polymerization was also retarded by durene or oxygen. A copolymerization with styrene at 0°C confirms a cationic mechanism, that is, the monomer reactivity