Salts onium borate

Radical Ions in Intramolecular ET and in Onium and Borate Salts... 

Radicals can be generated at the anode by oxidation of carbanions, alkyl borates, alkoxides, and carboxylates (see Chapter 22, Sec. V) and at the cathode by reduction of protonated carbonyl compounds or onium salts (see Chapter 10). Thereby, a wide choice of different radical structures can be mildly and simply obtained from readily available precursors. These radicals are especially suited for coupling and additive coupling reac-... 

Interestingly, TMAC, although it is insoluble in 2-pyrrolidone, apparently reacts with py-K/C02 and influences the outcome of the polymerization. On the other hand, other insoluble onium salts, such as tetramethylammonium perchlorate, tetrafluoro-borate, and hexafluorophosphate, are unreactive and give approximately the same conversion and molecular weight as the control run without onium salt. Anong the soluble onium salts tested, tetraethylammonium chloride and tetramethylammonium acetate are quite effective to increase conversion and molecular weight but are not better than the insoluble TMAC (Table IV). 

Many attempts have been made to find alternatives to the most reactive onium salt photo initiators bearing the AsFe" and SbFg" anions. These efforts have mainly been in response to the perception of toxicity and/or the possibility heavy metal contamination due to arsenic- and antimony-containing residues that are of concern in certain applications. In recent years, there has been considerable progress in the development of novel anions with weakly coordinating (i.e., low nucleophilic) character. For example, Castellanos et al7 have introduced diaryliodonium salt photoinitiators with the tetrakis(pentafluor-ophenyl)borate ((C6F5)4B ) anion. Following closely on this... 

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