Plasma polymerization of acetylene in a radio frequency discharge was studied under plug flow conditions in a box-type reactor with well-defined short range kinetic residence times beginning from the initial few milliseconds. Thin plasma polymerized films were deposited on semiconductor and metal surfaces and the process was monitored in situ by a quartz crystal microbalance and by optical emission spectroscopy. Pulsing the discharges provided a means of precise control of deposited thickness within a few angstroms, Secondary gas-phase products lake part in thf film formation beginning from about 30 to 40 ms of the kinetic residence time under the experimental condition. Post-discharge chemical reactions have a very small effect on the film thickness. The grafting, if any, of acetylene feed molecules on the plasma activated surface is negligibly small.