Spontaneous polymerization: Mechanism of initiation and paint process

Date of Completion

January 2001


Chemistry, Polymer|Plastics Technology




The mechanism for the formation of protective coatings on metal substrates by spontaneous polymerization has been investigated. In spontaneous polymerization several criteria must be met in order for a polymeric coating to form on a metal substrate. Firstly, a pair of monomers must form a donor/acceptor complex capable of accepting electron(s) from the substrate. Once the electron has been accepted, the monomer complex molecules continue to add to give a growing polymer chain. Secondly, the monomer pair must posses an affinity for the metal surface. If this affinity does not exist, no polymer will form or the polymer will not adhere to the surface. Thirdly, the metal substrate must be able to undergo at least one oxidative transition. The oxidation of the metal generates electrons that are accepted by the monomer complex and initiate polymerization. Fourthly, the cosolvent system must interact with the monomers. This interaction increases the long-term stability of the monomer solution by complexing with the monomers, thus decreasing the concentration of free monomer in the system. Various monomers were investigated: styrene, N-phenyl maleimide (NPMI), acrylonitrile, methyl acrylate and p-methyl styrene. Various solvents were investigated: N-methyl pyrrolidone (NMP), tetrahydrofuran, 2-(2-ethoxyethoxy)ethanol (DE), butyrolactone, and 1,3 and 1,5 dimethyl piperidone (DMPD). Various acids were investigated: sulfuric acid, citric acid and oxalic acid. Aluminum alloys of 5052 and 6061were investigated. Polymeric coatings were formed using the following monomer pairs: styrene/NPMI and p-methyl styrene/NPMI. Polymerization rates were conducted using NMP, DE and DMPD as the solvents and sulfuric, citric and oxalic acid as the acids. Rates were found to be independent of solvent but dependent on acid; sulfuric acid—1μm/min, citric acid—0.9μm/min, oxalic acid—0.5μm/min. Long term solution stability studies were conducted using 0.2M styrene, 0.2MNPMI, NMP as the solvent and sulfuric, citric and oxalic acid as the acids. The NMP/Sulfuric acid system remained stable for seven days, while NMP with either citric or oxalic acid remained stable for at least 20 days. ^ Along with the mechanism of spontaneous polymerization, a novel method for the application of spontaneous polymerization was developed and is described. This method was a paintable S-Poly® system. In this system there were two new requirements. The solution needed to be viscous and it needed to adhere at room temperature. The viscosity modifier that was investigated was poly(vinyl pyrrolidone) [PVP]. The room-temperature adhesion promoter that was investigated was γ-methacryloxypropyl trimetboxy silane. The optimum concentration for styrene and NPMI was increased from 0.2M to 0.3M in order to increase the driving force for polymerization. The optimum concentration of silane was determined to be 0.05M. The optimum concentration of PVP was determined to be 15 wt%. A typical coating thickness was determined to be 20μm. The adhesion of the final coating was not investigated. ^