Thin film plasma polymer (PP) coatings from a number of alkyl methacrylate precursors and their unsaturated analogues were deposited onto aluminium supports. Functional group retention and structural retention from the monomers were investigated as a function of the power (W) supplied to the plasma and the monomer flow rate (F) used in the polymerizations. The X-ray photoelectron spectroscopy and secondary ion mass spectrometry data reported herein show very clearly the importance of the W/F parameter in controlling PP chemistry and structure. Comparison of the PPs obtained from unsaturated and saturated monomers has allowed us to speculate on some aspects of the mechanism of polymerization.