Mass transfer of a penetrant plasticizer/simple gas mixture in block copolymers with a flexible fragment and rigid fragment, the latter containing active groups that enter into donor-acceptor relation with the penetrant plasticizer, was investigated for the case of the systems comprising a mixture of SO2-N-2/polyether (polyester) urethanes or polyether (polyester) urethane urea, polyarylate siloxanes having a block structure. Permeation of SO2 and N-2 in the block copolymers has been found to proceed through various fragments of polymer macromolecules.