Thermosetting film adhesives based on maleimide-modified-phenol-functionalacrylic copolymers

Pendant phenol-functional thermoplastic butylacrylate-acrylonitrile-maleimi dophenol (BNM) terpolymers synthesized by free radical copolymerization of butyl acrylate (BuA), acrylonitrile (AN), and varying proportions of N-(4-h ydroxy phenyl) maleimide (HPM) were cross-linked through different phenol g roup reactions. This included curing of the phenol group with a diepoxide a nd hexamethylene tetramine (HMTA), and thermal curing of the propargyl ethe r and cyanate ester groups derived from it. These thermosets exhibited good film-forming properties and their adhesive properties were evaluated using aluminium adherends. Cross-linking the polymers through phenol-epoxy react ion was found to be very effective in enhancing the mechanical and adhesive properties and for imparting a better thermoadhesive profile in comparison to the thermoplastic adhesive. Among the epoxy cross-linked (EpBNM) polyme rs, the optimum adhesive properties at ambient temperature were obtained fo r a polymer containing 9.5 wt% HPM. A single component thermosetting polyme r (GlyBNM) containing the optimum epoxy and phenol content was synthesized by copolymerization of glycidyl methacrylate (GMA) with BuA, AN, and HPM. W hen compared to EpBNM of identical composition, the adhesive properties of GlyBNM were inferior. Cross-linking of BNM through HMTA produced a brittle polymer with reduced adhesive properties. Thermal curing of the BNM polymer , after transformation of the phenol groups to propargyl ether and cyanate ester, did not enhance the adhesive properties, implying the superiority of the epoxy cross-linked system over the other systems.