Processable conducting polymers obtained via protonation of polyaniline with phosphoric acid esters

Abstract

The protonation of polyemeraldine base (PANI) by diesters of phosphoric acid was studied. Three esters were investigated, namely bis(2-methylpropyl) hydrogen phosphate (DiBHP), bis(2-ethylhexyl) hydrogen phosphate (DiOHP) and its non-branched analogue, bis(n-octyl) hydrogen phosphate (DnOHP). It has been found that DiOHP, in addition to protonation, plasticizes PANI at very low ester contents i.e. for y≥0.25 in PANI(DiOHP) y. In PANI(DnOHP) y and PANI(DiBHP) y the plastification starts at y=0.50 and y=0.65 respectively. It is clear that the long and branched substituents facilitate plastification. PANI protonated with DiOHP is soluble in common organic solvents such as toluene, chloroform, THF etc. The soluble fraction is enriched in DiOHP as compared with the parent protonated polymer. The existence of the anions originating from the ester in the soluble part of the polymer was confirmed by FTi.r. and 31P n.m.r. studies of the soluble fraction. Free-standing films with a conductivity of 10 S cm −1 can be produced by hot pressing PANI(DiOHP) y at temperatures of 80–140°C. At higher temperatures partial degradation of the complex occurs resulting in a decrease of conductivity with a simultaneous increase of Young's modulus and tensile strength. Blends of DiOHP-plasticized PANI and dioctyl phthalate-plasticized PVC, of excellent mechanical properties, can be prepared by hot pressing at 160°C.