Single-Step Electrochemical Synthesis of Composite Polymethylolacrylamide/Ultrafine Polytetrafluoroethylene

A single-step electrochemical synthesis of a composite of two nonconducting polymers is developed. For electropolymerization of acrylamide in the presence of ultrafine polytetrafluoroethylene (UPTFE) powder, it is shown that the electrochemical approach allows simplifying the traditional multi-step technologies of formation of composite polymer materials by combining in one process the acrylamide electropolymerization to form the polymethylolacrylamide (PMAA) film on the cathode, the capture of UPTFE particles by the growing polymeric matrix, and the formation of the PMAA/UPTFE composite. This technology allows shortening the total time of formation of the polymer/polymer composite to 5‒10 min. The procedure of preparation of stable aqueous dispersions of UPTFE is developed. It is shown that sodium lauryl sulfate (LS) and the siloxane-acrylate emulsion KE 13-36 are the most efficient stabilizers for the aqueous dispersion of UPTFE. The formation of the PMAA/UPTFE composite is confirmed by the methods of XRD, SEM, and SAXS spectrophotometry. It is found that the composite includes both coarse (~1 µm) and nanosized (1–10 nm) UPTFE particles. The transition of PMAA/UPTFE composite films from the colorless and transparent state typical of PMAA to the milk-white state (typical of UPTFE and KE 13-36) is observed. In the process, the transparency of composite films decreases reaching its minimum for PMAA/UPTFE/KE 13-36. As the electropolymerization time increases, the mass of the PMAA/UPTFE composite also increases and the residual current that characterizes the degree of electrode insulation decreases as compared with the PMAA coating. Modifying the film with ultrafine polytetrafluorethylene powder decrease the swelling capacity of composite coatings by a factor of 1.26–2.60 depending on the nature and concentration of the additive. The maximum insulation effect and the lower swelling capacity are reached for the PMAA/UPTFE(LS) composite which suggests the preferential use of UPTFE(LS) for modifying PMAA. The thermal stability is almost the same for the PMAA/UPTFE(LS) composite and the matrix PMAA.