Crosslinking poly(ethylene oxide) in dilute solutions by gamma rays

A high molecular weight poly(ethylene oxide) is gelled by radiation from a 60 Co source. At concentrations of 0.25 to 1 wt‐%, doses of 4.5 to 7.5 × 10 4 rad cause gelation. The storage modulus of the gel formed increases linearly with additional dose to a plateau value and then remains constant during further irradiation. The does needed to reach the plateau, D p in rads, and the plateau modulus G p in dynes per square centimeter, are related to the concentration c , in weight per cent: D p = 1.05 × 10 6 c and G p = 1.75 × 10 4 c 2.5 . The energy absorbed by the polymer per crosslink formed is about 80 ± 10 kcal/mol. The crosslink density produced by radiation is calculated from the measured modulus by using the theory of rubber elasticity. Both modulus and loss are measured in a special air‐bearing, recording torsion pendulum with a coneplate geometry.