Photoinitiated free radical polymerization of vinyl compounds in aqueous solution

Abstract

A new method for the photochemical initiation of polymerization of vinyl compounds in aqueous solution is described. The photochemically active species is an ion pair complex of the formula Fe3+X−(X− = OH−, CI−, N−3, etc.). The light absorption by the ion pair leads to an electron transfer causing reduction of the cation and oxidation of the anion to an atom or free radical X. The latter leads to the initiation of polymerization in accordance with X + CH2CHR→XCH2CHR. The kinetics of the reaction were studied by the measurement of: (a) ferrous ion formed (colorimetrically), (b) monomer disappearance (by titration and by weighting the polymer), (c) the chain length of the polymer (in the case of methyl methacrylate). The dependence of the quantum yield on the light intensity, light absorption fraction, and the concentration of vinyl monomer and ferrous ion added initially was investigated. A complete mechanism, both with regard to the formation of free radicals and the polymerization reaction, was put forward involving: (1) light absorption, (2) a primary dark back reaction, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation of polymerization by free radicals, (6) propagation of polymerization, and (7) termination by recombination of active polymer endings. The mechanism was verified by the experimental results and some constant ratios were estimated quantitatively.

Primary Photochemical Reactions in the Photo-Fenton System with Ferric Chloride. 1. A Case Study of Xylidine Oxidation as a Model Compound

“…This rate constant is in reasonable agreement with the published data of 3.1 × 10 9 (M s) -1 as shown in eq16 Assuming that the decay Cl2 •occurred with reaction 16, an estimation of k16 could be made as 1/[(120 × 10 -6 )‚(4 × 10 -6 )] ) 2.1 × 10 9 (M s) -1 .…”

Photodegradation of organic pollutants in aqueous solutions caused by Fe(OH)aq2+ photolysis: Evidence of OH radical formation

“…It is believed that the photolysis of Fe(III) hydroxocomplexes leads to the formation of hydroxyl radical via intramolecular electron transfer from the coordinated OH − anion to the central ion of the lightexcited complex. This mechanism was based mainly on the analysis of the final products of photochemical reactions between light-excited Fe(III) complexes and organic compounds [4][5][6][7][8][9][10][11][12][13][14][15][16]. Actually, the primary mechanism of the photolysis could not be examined in stationary experiments.…”

Preparation of Bead–String Shaped Attapulgite/Poly(methyl methacrylate) Particles by Soapless Emulsion Polymerization Based on UV Irradiation in the Presence of Iron(III)

“…In this work, we used FeCl 3 as a photoinitiator to prepare ATP/PMMA particles. The likely mechanism of photoinitiation using Fe 3+ as photoinitiator has been reported by Evans et al (22). It has been found in our research that it possesses high efficient photoinitiation even though using a small percentage of photoinitiator.…”