SYNTHESIS OF PERFLUORINATED CATION-EXCHANGE MEMBRANES BY PREIRRADIATION GRAFTING OF ACRYLIC-ACID ONTO ETHYLENE-TETRAFLUOROETHYLENE FILMS

Hydrophilic carboxyl-containing fluoromembranes were obtained by preir radiation grafting of acrylic acid onto ethylene-tetrafluoroethylene f ilm. The dependence of the grafting reaction on temperature, monomer c oncentration, nature and concentration of inhibitor, crosslinking agen t, solvent, and on the preirradiation dose was investigated. The graft ing rates increase with temperature, whereas the saturation degree of grafting (SDG) decreases. Addition of inhibitor minimizes homopolymeri zation and at the same time hinders the grafting reaction. The SDG inc reases markedly with monomer concentration until it reaches a maximum and thereafter decreases. The grafting rates increase with preirradiat ion dose. Addition of crosslinking agent initially decreases the SDG, and thereafter increases. The highest grafting rates are obtained usin g water as solvent followed by methanol and ethanol. The results are d iscussed on the basis of various parameters: interaction between monom er diffusibility and the viscosity of the monomer bath, the mutual rea ctivity of monomer, and the crosslinking agent. An agreement is observ ed between the values of the electrical resistance and the saturation degree of grafting. (C) 1996 John Wiley & Sons, Inc.