Oxygen barrier coatings based on supramolecular assembly of melamine

Gas permeability is one of the key performance characteristics of polymeric films. Here we explore a novel approach for modifying the oxygen transmiss ion rate of polymers by vapor deposition of melamine. We win show that mela mine, upon physical vapor deposition, forms a transparent uniform layer on polymeric films such as biaxially oriented polypropylene. X-ray diffraction , in combination with molecular modeling, has indicated that the melamine c oating is crystalline and macroscopically oriented with the preferred direc tion of the melamine molecules parallel to the (polymeric) substrate. The v apor-deposited melamine molecules undergo a large number of cooperative hyd rogen bond interactions leading to a coherent layer of an infinite supramol ecular network. The melamine coating acts as a surprisingly effective barri er against gases, decreasing drastically, for example, the oxygen transmiss ion rate through coated polymer films by 2 orders of magnitude. The effect is attributed to the crystalline nature of the deposited melamine layer, st rengthened by the high level of hydrogen bonding. This is the first example of application of supramolecular chemistry for the production of health an d environment friendly transparent barrier coatings against oxygen. The vac uum-coating process with melamine and related compounds is expected to brin g a major breakthrough in the field of transparent polymeric barrier films for applications, for example, in food and pharmaceutical packaging.