Chemical modification of perfluoropolyether oligomers and effects on compatability and properties of epoxy resins

The incorporation of fluorine in epoxy resins has been the focus of research for many years, aiming to reduce water absorption and to improve the degradation resistance in hot-moist environments. To this end resins have been synthesised from fluorinated monomers while crosslinking was induced by conventional hardeners. In the present work conventional diglycidyl ether of bisphenol A epoxy resins were modified by the addition of small amounts of perfluoropolyether oligomers containing functional groups at the chain ends. Compatibilisation of these oligomers in epoxy resins was achieved through end-capping and chain extension reactions. Such modifications of the fluoroligomers only affect marginally the viscosity of the resin mixture. Using hexahydrophthalic anhydride as the main hardener and through selective curing procedures the morphology of the crosslinked resins was controlled to. produce either transparent formulations, consisting essentially of an IPN monophase structure, or opaque systems containing precipitated spherical particles. Perfect adhesion is exhibited at the particle interface with the matrix, i.e. there was a complete absence of de bonding during fracture[continued]...