Poly(ethylene-alt-tetra-fluoroethylene (ETFE) and poly(tetrafluoroethylene-cohexafluoropropylene) (FEP) were pre-irradiated under air using a Co⁶⁰ gamma source to graft styrene at low pH. Grafting copolymers were tuned by study of different parameters (monomer, reaction time, temperature, and pH with addition of sulfuric acid (H₂SO₄)). The maximum degree of grafting was 80% and 40% for ETFE and FEP respectively at dose 2 kGy. Influence of low pH in grafting degree by adding sulfuric acid was studied. Grafting degree was examined by infrared (FTIR-ATR), differential scanning calorimetry (DSC) and swelling behavior analysis after sulfonation process.