Grafting of acrylic acid onto radiation-peroxidized polypropylene film in the presence of ferrous ion

Acrylic acid has been grafted from aqueous solution onto 70 μ isotactic polypropylene-film previously peroxidized by irradiating in air with both 400 keV electrons and γ-radiation from a ⁶⁰Co source. Ferrous ion has been used to induce the redox decomposition of the macromolecular peroxy species at temperatures between 0 and 40°C. It has been shown that the effect of low Fe²⁺] is to increase grafting rates, but that at Fe²⁺] > 8 × 10^?4 molal the retarding effect of the reducing ion becomes increasingly important. At constant Fe²⁺] a pronounced maximum in rate is observed at around 50 wt-% of acrylic acid; this may be related to increased swelling of the polymer matrix at this point. The initial rate of grafting increases as the square root of the preirradiation dose and, in the preirradiation dose rate range, 1.6–8.0 Mrad/sec, is independent of the dose rate. The grafting rate during the later stages of the reaction, however, increases as the preirradiation dose rate decreases. In the temperature range 0–40°C, the overall activation energy is 19 kcal/mole; from this value, the activation energy of initiation has been estimated to be around 20 kcal/mole.