Synthesis, curing and physical behaviour of maleimide-terminated poly(ether ketones)

Maleimide-terminated amorphous poly(arylene ether sulphones) and poly(arylene ether ketones) of controlled M ̄_n (2000-10000 or higher) were synthesized by nucleophilic aromatic substitution, step polymerization and bisphenol A phenolate with activated aromatic halides in the presence of m-aminophenol or 2,2′-(4-aminophenyl-4-hydroxyphenyl)propane. The amine-terminated oligomers of predictable molecular weight were then converted to maleimides. This 'two-step' method was accomplished by reacting the terminal amine with maleic anhydride in a co-solvent of N-methylpyrrolidone N-cyclohexyl pyrrolidone ( 80 20). A second 'one-step' oligomer synthesis method employed either m-maleimidophenol or 2,2′-(4-maleimido-4′-hydroxyphenyl)propane as the 'monofunctional' end-capper. The oligomers were thermally crosslinked through a free-radical reaction of the maleimide end-groups. Curing at 250°C for 1 h produced networks which were 98% chloroform-insoluble. The influence of oligomer molecular weight on the thermal and mechanical properties of the solvent-resistant networks was investigated by differential scanning calorimetry, dynamic mechanical thermal analysis, flexural modulus and fracture toughness, K_IC. Very substantial increases in toughness were observed relative to simple bismaleimides and were a function of the molecular weight between crosslinks ( M ̄_c) and the β-relaxation of the matrix.