Study on the mechanism of the cationic polymerization of cyclohexene oxide initiated by the photosystem of poly(methyl phenyl silane) and pyridinium salts

The initiation process of photoinduced polymerization of cyclohexene oxide (CHO) in the presence of pyridinium salts and poly(methyl phenyl silane) (PMPS) was investigated by CW-ESR, time-resolved ESR, F-19 NMR, and by the polymerization behavior with three kinds of pyridinium salts. The results of CW-ESR measurements suggest that photolysis of PMPS under UV irradiation at wavelength longer than 310 nm mainly through main-chain scission. The facts that the life time of the transient radicals of PMPS under irradiation decreased significantly when N-ethoxy-2-methyl pyridinium hexafluorophosphate (EMP(+)PF(6)(-)) was added suggest that single electron transfer from the silyl radicals to EMP(+) ions took place. The polymerization of CHO could be easily initiated by irradiation (lambda(inc) = 345 nm) on dichloromethane solutions of CHO containing EMP(+)PF(6)(-) and PMPS. However, no polymerization of CHO took place when ClO4- or I- was the counter ion of EMP(+) ions. This effect of the counter ion on the polymerization of CHO indicates that the silylenium ion, obtained by the electron transfer reaction from silyl radical, hardly initiates the polymerization of CHO. When the counter ion of EMP(+) ion is PF6-, PF5, produced by the reaction of silylenium ion with PF6-, is considered to be an initiator for the polymerization of CHO, because Si-F bond, which is obtained by the F- abstraction of silylenium ion from PF6-, was found in residual hexane-insoluble polysilanes by F-19 NMR spectroscopy.