Low density polyethylene can be modified by acrylic acid sorption and in situ thermal polymerization and grafting, at 60-90°C. Iron (III) oxide dispersed on low density polyethylene increases the extent of acrylic acid sorption and polymerization/grafting, both in (X-ray) preirradiated and non-preirradiated polyethylene. This effect is better observed at 60°C. The ratio between the weight gain on non irradiated and preirradiated matrix is higher at 60°C than at 90°C. © 1986 Springer-Verlag.166499505