PHOTOOXIDATION OF POLYDIMETHYLSILOXANE OILS .3. EFFECT OF DIMETHYLENEGROUPS

Photo-oxidations at wavelengths longer than 300 nm of polydimethylsilo xanes (PDMS) formed by hydrosilylation reactions (i.e. containing dime thylene (approximately CH2-CH2 approximately) and methine [GRAPHICS] g roups) have been examined. The consumption of initial functional group s and the appearance of new groups derived from the photo-oxidation we re followed by FTIR. H-1, C-13 and Si-29 NMR and GC/MS. The main photo -oxidation process is the hydroperoxidation of dimethylene groups and the photoscission of hydroperoxide groups into beta-silylated carboxyl ic acid (approximately SiCH2-COOH) and silanol groups (SiOH). A small part of the silanols formed is condensed into ester and siloxane group s.