Synthesis of Dihydroxy-Terminated Poly (2,2,3,3,4,4-Hexafluoropentane-1,5-Diol Formal).
Patent Application, Filed 5 May 87,
DEPARTMENT OF THE NAVY WASHINGTON DC
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This invention relates to fluoropolymers and more particularly to dihydroxyl-terminated poly2,2,3,3,4,4-hexafluoropentane-1,5-diol formal. The copolymerization of diols with formaldehyde has in the past been accomplished by a number of means. Originally, the most common method employed was acid transformylation of the diol with a dialkyl formal. Usually, the acid catalyst was p-toluenesulfonic acid. This procedure, however, required high temperatures and constant removal of the alcohol byproduct in order to drive the reaction forward to good yield. Subsequently, formation of polyformals has been achieved by reaction of the diol with formaldehyde either in the form of paraformaldehyde or in the form of trioxane. The procedures also called for reactions to take place at high temperatures, in a water immiscible solvent, and in the presence of an acid catalyst. Water byproduct formed during the polycondensation process was also required to be removed by azeotropic distillation in order to drive the reaction forward to good yield. Alternatively, synthesis of polyformals has been carried out by acid catalyzed ring opening polymerization of the performed cyclic formal.
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