A plastic container, preform or article includes a multilayer wall having at least one layer of matrix resin, at least one layer of barrier resin, and an adhesion-promoting material blended with the barrier resin and/or the matrix resin to promote bonding between the barrier and matrix layers. The matrix resin preferably is an ester-containing resin, most preferably a polyester such as PET. The adhesion-promoting material includes an amine polymer, preferably an imine polymer having a plurality of available primary, secondary or tertiary amine groups. An alkylene imine polymer is preferred, particularly a polyethyleneimine polymer.