Chemistry of some model compounds related to fluorinated polymers
The work described in this thesis is concerned with three areas which are the generation of stable carbocations from saturated model compounds related to poly- vinylidenefluoride, the development of synthetic routes to fluoro-organo-phosphazenes with intention of obtaining some potential additives for perfluoropolyether fluids operating at elevated temperatures, and pericyclic reactions involving fluorinated olefins.1. We reported that some remarkable conjugated cations, and di-cations (4a) are obtained by reaction of hydrofluorocarbon precursors (4) with an excess of antimony pentafluoride. Cations (4a) bear the fluorine atoms at the charged sites, which of course, leads to stabilisation of the systems We investigated the effect of both re-hybridisation and charge on (^13)C, (^19)F, (^1)H n.m.r. chemical shifts and we applied the empirical criterion of (^13)C chemical shifts additivity to these systems to confirm the structure of some carbo-mono-cations and.-di- cations.2. The mechanism of displacement reactions in halophosphazenes was rationalised by reacting the systems in study with selected nucleophiles in competition reactions. Some fluoro-organo-phosphazenes were synthesised using halophosphazenes as starting materials. Different methodologies were used and their effectiveness was limited by the reactivity of the halophosphazenes towards the fluoroalkylating agents. The methodologies used include nucleophilic displacement of the halogen with fluorinated alcohols (R(_F)CH(_2)OH), and perfluoroalkylating agents (eg.: CF(_3)SiMe(_3)); perfluoroalkylation of organo-phosphazene using hexafluoropropene under gamma ray irradiation. Potential stabilising agents for perfluoropolyether fluids were synthesised and their effectiveness was tested.3. Some pericyclic reactions of heptafluorobut-2-ene and hexafluorobut-2-ene with dienes have been studied in an attempt to synthesise a series of benzenoid and heteroaromatic compounds containing two trifluoromethyl groups in high yields.