An investigation of plasma polymerization and copolymerization using fluoroaromatic compounds

Abstract

The work detailed in this thesis concerns polymers synthesised by R.F. inductively coupled plasmas excited in fluorine containing monomer vapours. The structure and bonding in a series of polymers prepared from per-fluoroaromatic monomers by plasma polymerization was investigated by ESCA. The composition and structural features of these films were compared and contrasted with each other and with plasma polymers derived from the same parent compounds with lower degrees of fluorination. Critical emission spectra, ~260-600nm, from these plasmas were recorded and a correlation made between certain species fluorescing in the gas phase and functional groups within the polymer. An association hcis also been made between the peaks at ~280 and ~510nm in the optical emission spectrum. Difluorocarbene is responsible for the peak at ~280nm but the peak at 510nm has an unknown origin. The effect of copolymerizing a fluoroaronatic compound with a second component on polymer composition has been examined, where the comonomer has ranged from an inert gas to an organic hydrocarbon analogue. Copolymerizaticn resulted in a stabilisation of the rearrangement mechanisms normally associated with the plasma polymerization of a perfluoroaromatic compound; CF=CF(_n) and CF(_2) groups were greatly reduced in intensity in the ccpolymer. The binding energy of the CF-CF(_n) peak indicated that the component peak was, in fact, due to CF-CF(_aromatic) i.e. copolymerization had also resulted in a greater retention of the aromatic nature of the parent fluorocotpound. Polymers were also prepared by irradiating the monomer vapour with wavelengths >130nm. Perfluorobenzene could not be polymerized with UV irradiation of wavelengths greater than 200nm, but could however be polymerized with wavelengths below 200nm. This produced a polymer whose composition, as determined by ESCA, was very similar to the composition of plasma polymers derived from the same monomer indicating that the mechanisms involved in both polymerizations are similar. Vibrationally excited ground state perfluorobenzene is thought to be involved in the reaction pathway.