The synthesis and chemistry of model compounds related to fluoropolymers
The objectives of this research project were to synthesize and investigate the chemistry of model compounds related to the hexafluoropropene/vinylidene fluoride copolymer system. A number of compounds of this type were prepared which underwent a series of reactions in order to obtain definitive information about the chemical processes occurring during the cross-linking of the copolymer system with bis-nucleophiles. Further studies with the model compounds also indicated potential sites in the cured copolymers through which chemical degradation could take place, during their use in aggressive environments. Other investigations with the model compounds, together with unsaturated compounds derived from these systems, led to the observation of some very unusual chemistry. Lewis acid induced dehydrofluorination reactions with antimony pentafluoride led to the formation of a number of observable carbocations and a unique contiguous dication. This methodology was further developed in the treatment of saturated homopolymers, in which dehydrohalogenation by antimony pentafluoride led to formation of polyacetylene derivatives displaying intense colouration. In order to circumvent the formation of potential sites of chemical instability during the curing process with nucleophiles, a methodology was investigated in which cross-linking could occur via a free radical mechanism involving hemolytic bond cleavage of sterically demanding groups. A number of monomers containing a bulky pendant group were prepared and were investigated in order to determine their suitability to undergo copolymerisation with vinylidene fluoride. Copolymers obtained in this way were then examined to determine whether polymer radicals could be produced by thermally induced hemolytic bond scission of sites involving the sterically crowded groups. The results obtained clearly demonstrated that this type of cross-linking process is entirely feasible.