Photochemical, Electrochemical, and Radiation Initiation

Photochemical, Electrochemical, and Radiation Initiation.— In contrast to conventional chemically-induced cationic polymerizations, photo-polymerizations, electro-polymerizations and radiation polymerizations require the application of energy from a source external to the reaction medium. 

Jedlinski, J. Lukaszczyk, J. Dudek, and M. Gibas, Amer. Chem. Soc. Polymer Preprints, 1977,18(1), 671. 

The topic of photo-initiated cationic polymerization has been reviewed in-depth recently by Crivello, who has also co-authored a series of reports on the development of diarylhalonium salts for use as photo-initiators. These salts are claimed to decompose in the presence of ultraviolet light and react with solvent molecules to yield Bronsted acids with stable counterions, as shown in reactions (4)—(6), where S—H is a solvent molecule. These acids are the initiating species 

A reaction scheme similar to that outlined above has been proposed to account for the photo-initiation of cationic polymerizations by triarylsulphonium salts, and a systematic comparison of the [x Iymerization behaviour of various epoxides in the presence of sulphonium and iodonium salts has been conducted. More recently the concept of sulphonium salt photo-initiators has been extended to include thiopyrylium salts.  

The electro-initiated polymerization of indene in the presence of supporting electrolytes such as tetraethylammonium hexachloroantimonate has been studied by Bhadani and his co-workers. Polymerization behaviour appeared to be independent of the nature of the electrode material and the reactions gave rise to low molecular weight polymers with unsaturated end-groups. 

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