A pulsed-arc atmospheric pressure air plasma jet has been used to deposit plasma polymerized acrylic acid/methylene-bis-acrylamide (ppAA/MBA) organic thin films. Optical emission spectroscopy has been performed to investigate the reactivity of the plasma and the dissociation of the precursor as a function of the pulse frequency and distance from the nozzle. An estimation of the OH rotational temperature, which is an indicator of the plasma gas temperature, has also been performed. By heating the substrate during deposition, it was possible to improve to a great extent the stability to water of the coatings. Stable ppAA/MBA films have been obtained with an air plasma over a large range of pulsed frequencies (from 15 to 25 kHz) when the substrate was heated to 200 A degrees C. The composition of these coatings was investigated by FTIR and different amide/acid ratios were obtained, showing the possibility to grow stable films with different functional groups by adjusting the deposition parameters.