Katalin Dajka

Kinetics of the early stages of high‐energy radiation initiated polymerization

We describe our method based on pulse radiolysis with optical detection developed for the examination of the kinetics and mechanism of the first steps of high-energy radiation initiated polymerization. The absorption spectra of the intermediates were obtained in cyclohexane solution of hexanediol diacrylate (HDDA) of different concentrations. In dilute solution (10 mmol . dm -3 ) and short time (10 μs) after the pulse, the spectrum of the monomer radicals was observed. On increasing the monomer concentration, the maximum of the spectrum was shifted to longer wavelength indicating the start of the oligomerization reaction. The increase in the time of observation resulted in a similar shift in dilute solution. From the kinetic curves the rate coefficients of termination for the monomer radical (2 . k t ) were determined. The average rate coefficient of termination was found to decrease in time (that is with increasing chain-length).

Protonation kinetics of acrylate radical anions

The radical anions of acrylamide, methacrylamide and 2-hydroxypropyl acrylate were produced by pulse radiolysis of moderately acidic aqueous solutions well below the pKa of the radical anion. The rate coefficients of protonation were determined by UV kinetic spectroscopy at wavelengths where the protonated and ionic forms have considerably different absorbances. The rate coefficients of protonation were measured as (6.0±0.9)×1010, (6.6±1.0)×1010 and (5.0±1.0)×1010 mol−1 dm3 s−1. Using these rate coefficients and the pKa values of the radical anion, 7.9, 8.0 and 5.5, the rate coefficients of deprotonation were determined as 7.5×102, 6.6×102 and 1.6×105 s−1. The results clearly showed that in acidic solution the protonation occurred with H3O+ and not with H2O. The rate coefficients determined were discussed and compared with relevant data in the literature.

Study of high-energy radiation initiated polymerization of butyl acrylate

Abstract The kinetics and mechanism of the first steps of radiation initiated polymerization was studied in cyclohexane solution of butyl acrylate applying pulse radiolysis with optical detection. By increasing the monomer concentration, the shape and wavelength of the maximum of the spectrum was changed indicating the start of the oligomerization reaction. From the kinetic curves average rate coefficients of termination for the oligomer radicals (2 k t ) were determined. They were found to decrease in time (that is with increasing chain-length).

On the reversible protonation of acrylic-type compounds

The pseudo-first-order protonation rate coefficients of radical anions of acrylic-type monomers (produced by pulse radiolysis in aqueous acidic solutions) were found to be linearly dependent on the H3O+ concentration with second order rate coefficients of several times 1010 mol-1 dm3 s-1. The rate coefficients showed little structure dependence. On the contrary the equilibrium constants of protonation and therefore also the rate coefficients of deprotonation showed several orders of magnitude dependence on the anion structure. In the paper this structure dependence is discussed.