An investigation of the plasma polymerisation of organic compounds and its relationship with surface photopolmerisation
Plasma polymers of perfluorobenzene (PFB), perfluorotoluene (PFT), perfluorocyclohexane, perfluorocyclohexene, benzene, naphthalene and N-vinyl pyrrolidinone (NVP) were prepared and analysed by XPS and SIMS. The analysis suggested that polymers derived from perfluoroaromatic monomers consisted of aromatic and other cyclic structures linked by very short alkyl chains, while those derived from perfluorocyclohexane and perfluorocyclohexene were much more aliphatic in nature and contained fewer aromatic and other ring structures. PFB, PFT and NVP were found to produce surface photopolymers, similar to their plasma polymers, suggesting that the polymerisation proceeds via an excited state mechanism. The photopolymerisat ion of NVP was found to be either a one or two photon process depending on the conditions used, and an approximate lifetime was found for a polymerising gas phase species. Plasma mass spectroscopy also suggested that neutral species were largely responsible for the plasma polymerisation of PFB, but that ionic species were important in the plasma polymerisation of benzene. Considerable gas phase interaction was observed in a mixed benzene/PFB plasma. Plasma polymers containing a high concentration of -COOH were formed from a variety of carboxylic acids, by using low power and high flow rate conditions, but methyl methacrylate and acetic acid did not retain their carboxylate groups under similar conditions. Iodine was incorporated into a plasma polymer by copolymerising benzene and iodobenzene, but not at a sufficiently high concentration to prevent oxygen plasma etching. Plasma polymerisation of allyl iodide produced a polymer containing I(_3)(^-) ions.