Redox systems thiourea

This kind of redox system leads also to other free-radical species and the obtained polymers are not purely hydroxytelechelic. Hydroxylamine/mineral acid (HC1, H2S04)/H202 55 59,60), NaHS03/H202 55), ascorbic acid/H202 61), thiourea (or N-substituted thiourea)/H202 62 -64) systems have been suggested. The last one yields mostly hydroxyl-terminated polymers. 

There are other initiator systems of lesser commercial importance. Cumene hydroperoxide is reported to cure acrylic adhesives in the presence of alkyl or pyridyl thioureas [105]. These initiators have been combined with a phosphated acrylate to promote adhesion to metal [106]. Thiourea-based initiators can be applied as a one-part on galvanized metal, where the metal surface provides the second part of the redox initiator [107]. 

Redox processes in gold(iii) systems involving initial fast substitution steps have been described in previous volumes of this Report. Further examples are given by the reactions between [AuCh]" and dialkyl sulphides and thiourea. Both reactions take place in two discernible steps. The first corresponds to the formation of substitution products in equilibrium with [AuCl4], and the second one to the reduction of the gold(iii) species to gold(i). 

The many papers on redox initiation include studies of very varied systems, e.g., persulphate with thiomalic acid, hydrogen peroxide with thiourea, and manganese(n) with ascorbic acid. Kinetic and mechanistic complications... 

Only a few of the initiators suitable for polymerizations in aqueous systems have been fully investigated recently described initiators for such systems include new redox combinations, e.g. the ceric ion with thiourea, lithium peroxydiphosphate, and various azo compounds. <... 

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