AbstractThe modification of polyethylene by the grafting of poly(acrylic acid) onto the surface of one of the faces of low‐density polyethylene films with UV radiation is reported. The transport of oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, ethane, ethylene, propane, and argon across surface‐modified films containing 3.7% poly(acrylic acid) has been investigated at several temperatures. The layer of poly(acrylic acid) grafted onto the surface of one of the faces of the films reduces the permeability coefficient of the gases by a factor of about 1/6. The sharp drop in the gas permeability as a result of the poly(acrylic acid) layer may arise either from the formation of ordered structures of the grafted chains or from the development of highly crosslinked structures. The values of the polymer–gas enthalpic interaction parameter for the modified film are higher than those for the unmodified one. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2828–2840, 2006