AbstractPoly(vinylidene fluoride), polytrifluoroethylene, and two rubbery copolymers with vinylidene fluoride were crosslinked by γ‐irradiation in vacuum. Radiation‐induced chain scissions in the copolymers were studied by observing the relaxation of stress at constant extension during further irradiation at 27°C., at 0.31–2.7 Mr./hr. in nitrogen and in air. From gel content, swelling, and elasticity, the values of Gc (crosslinking) and Gd (scission) were respectively; for CF2CFH, Gc = 2.2 and Gd = 0.4; for CF2CH2, 2.0 and 0.3; for CF2CH2 + C3F6, 3.4 and 1.3; for CF2CH2 + CF2CFCl, 1.8 and 1.4. The Gd values from stress relaxation were variable; the lowest were: for CF2CH2 + C3F6, 4.6 in nitrogen and 8.4 in air; for CF2CH2 + CF2CFCl, 1.9 in nitrogen and 3.6 in air.