Octadecyl acrylate monolayers were polymerized at the nitrogen-water interface. The reaction was initiated by UV radiation and followed by measurement of surface potentials, relative surface viscosities and infrared spectra. Product behavior suggested a high molecular weight and cross-linked polymer. There were some indications that the interfacially polymerized material was stereoregular. The reaction was complicated by UV induced degradation of poly(octadecyl acrylate) monolayers to a product which showed many of the characteristics of poly(acrylic acid).