The invention relates to a process for the prepn. of a gas barrier film, comprising 1) providing an olefin copolymer comprising: (i) recurring units A derived from an olefin and (ii) recurring units B derived from a compd. according to formula (I), (II) or (III): (I) wherein R1 is selected from -H or -CH3; R2 is selected from -0-, -(CO)-(NH)- or -(CO)-O-; R3 is a moiety comprising 1 -30 carbon atoms; and n is an integer between 1 and 10, (II) wherein R1 is selected from -H or -CH3 and p is an integer between 1 and 10, (III) wherein R1 is selected from -H or -CH3 and q is an integer between 1 and 10, 2) grafting a graft compd. represented by the formula (IV) or (V) to the olefin copolymer (IV) wherein R4 is independently -H, C1 -C10 linear, branched or cyclic alkyl; X is -NH- or -O- and R5 is represented by the formula: (A) where r is an integer between 1 and 20; Y is -NCO, halogen (I, Br, CI, F), -Si(OMe)3, -N=C=S, -N3, -COOH, an amino acid or an amino ester, (V) wherein each of R6, R7, R8 and R9 is independently -H, C1 -C10 linear, branched or cyclic alkyl; X is -NH- or -O- and R5 is represented by the formula: (A) where r is an integer between 1 and 20; Y is -NCO, halogen (I, Br, CI, F), -Si(OMe)3, -N=C=S, -N3, -COOH, an amino acid or an amino ester and 3) shaping the grafted polymer obtained by step 2) into a film
