latex of acrylate esters preferred copolymers can include poly butyl methacrylate 2 dimethylaminoethyl methacrylate methyl methacrylate 1 2 1 150 000 sold under the trademark eudragit e poly ethyl acrylate methyl methacrylate 2 1 800 000 sold under the trademark eudragit ne 30 d poly methacrylic acid methyl methacrylate 1 1 135 000 sold under the trademark eudragit l poly methacrylic acid ethyl acrylate 1 1 250 000 sold under the trademark eudragit l poly methacrylic acid methyl methacrylate 1 2 135 000 sold under the trademark eudragit s poly ethyl acrylate methyl methacrylate trimethylammonioethyl methacrylate chloride 1 2 0 2 150 000 sold under the trademark eudragit rl poly ethyl acrylate methyl methacrylate trimethylammonioethyl methacrylate chloride 1 2 0 1 150 000 sold as eudragit rs in each case the ratio x y z indicates the molar proportions of the monomer units and the last number is the number average molecular weight of the polymer especially preferred are cellulose acetate containing plasticizers such as acetyl tributyl citrate and ethylacrylate methylmethylacrylate copolymers such as eudragit ne the foregoing materials for use as the barrier layer can be formulated with plasticizers to make the barrier layer suitably deformable such that the force exerted by the expandable layer will collapse the compartment formed by the barrier layer to dispense the liquid active agent formulation examples of typical plasticizers are.