Thermosetting film adhesives based on maleimide-modified-phenol-functional acrylic copolymers

Pendant phenol-functional thermoplastic butylacrylate-acrylonitrile-maleimidophenol (BNM) terpolymers synthesized by free radical copolymerization of butyl acrylate (BuA), acrylonitrile (AN), and varying proportions of N-(4-hydroxy phenyl) maleimide (HPM) were cross-linked through different phenol group reactions. This included curing of the phenol group with a diepoxide and hexamethylene tetramine (HMTA), and thermal curing of the propargyl ether 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 reaction 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) polymers, the optimum adhesive properties at ambient temperature were obtained for a polymer containing 9.5 wt% HPM. A single component thermosetting polymer (GlyBNM) containing the optimum epoxy and phenol content was synthesized by copolymerization of glycidyl methacrylate (GMA) with BuA, AN, and HPM. When 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.