PHOTO-INDUCED AND RADIATION-INDUCED CHEMICAL GENERATION AND REACTIONS OF STYRENE RADICAL CATIONS IN POLAR AND NONPOLAR-SOLVENTS

Radical cations of the substituted styrenes (M) 1-10 have been produced by pulse radiolysis of solutions of M in cyclohexane. The monomer radical cations, M(.+), are formed by fast electron transfer from the solute, M, to the solvent radical cation produced by the ionizing radiation. The decay of M(.+) proceeds by an ion-molecule reaction with the parent styrene (dimerization; k = 0.6-1.0 x 10(10) dm(3) mol(-1) s(-1)) resulting in head-to-head connected distonic dimer radical cations which show properties of carbenium ions. At high styrene concentrations a trimerization which represents the start of the free cationic polymerization takes place with a rate constant of ca. 10(6) dm(3) mol(-1) s(-1). In aqueous or alcoholic solutions, radical cations were generated by direct two-photon ionization (indicated by the presence of the solvated electron) of the styrenes or by reactions with strong oxidants, such as SO4.- and Tl2+, generated by laser UV photolysis as well as by pulse radiolysis. Only for 4-methoxystyrene 6 and trans-anethole 7 could the (monomeric) radical cations be directly observed in the nanosecond to millisecond range. In the other cases, the radical cations decay within the sub-nanosecond timescale by reaction with H2O forming beta-hydroxybenzyl type radicals.