Oligomeric Products in Plasma=Polymerized Organosilicones

Plasma polymers were deposited from a number of methylsilazane and methylsiloxane monomers of linear and cyclic structure. The oligomeric phase evolved from the polymers by a mild thermal treatment was analyzed using gas chromatography/mass spectrometry combined techniques. The oligomeric phase was found to be composed of the low-molecular-weight products with the weight being mostly no higher than two monomer units. The results suggested that the oligomers might be formed in the gas phase and then they diffuse to the surface of the growing polymer film. The structure of the oligomeric products indicated that their formation must proceed via the Si-N and Si-O bonds fission in silazane and siloxane monomers, respectively. An ionic nature of the primary active species involved in this process was assumed owing to the high susceptibility of these bonds toward heterolytic fission. The postulated ionic mechanism, considered to account for the formation of the observed oligomers, seems to be more reasonable than the radical mechanism. Pyrolysis/gas chromatography and infrared investigations of plasma polymers revealed that methylsilyl groups in the monomers were highly susceptible to form disilymethylene and disilymethylene and disylyethylene cross-linkages. This process was assumed to proceed via homolytic fission of the Si-C and C-H bonds in methylsilyl groups and subsequent recombination of formed radical species. Based on these results, the elementary reactions contributing to the overall plasma polymerization processes of both ionic and radical mechanisms were formulated.