Donald A. Seanor

Metal catalysed oxidative coupling of mercaptan-containing poly(dimethyl siloxanes)

Abstract The oxidative coupling of mercaptan-containing poly(dimethyl siloxane) polymers: catalysed by different metals has been studied. In the presence of excess oxygen, the kinetics obey the law, d(SH) d t = −k( SH ) n , where n = 0 or 2 dependent upon temperature and the specific metal. The rate constant, k, is independent of x and y in the range studied but is a function of the metal. An activation energy of 18.4 ± 0.6 kcal/mol was found. It is postulated that the following sequence of reactions occurs: Depending upon the metal and temperature, desorption (step 3) or reaction (step 2) may be the ratelimiting step. Steps (3) and (4) may occur simultaneously. Metals for which no oxidation/reduction couple exists show little catalytic effect even though a strongly bonded interfacial layer is formed. The interfacial layer which formed rapidly was studied via reflection spectroscopy and protective ability. It is strongly bonded, of low critical surface energy and consists primarily of: However, it is enriched in sulphur over the bulk polymer.