Development of electroactive polymers for application in anti-corrosion formulations.

Corrosion is a major environmental and economic problem with many modern manmade structures heavily relying on the utilisation of metals and alloys due to their extraordinary strength, mechanical and physical properties. Applications such as those seen in the construction industry, aerospace and marine industries, all of which need a constant protection and barriers against the harsh environmental conditions. Current methods of protection employ the use of chromates in paint formulations for the active anti-corrosive paints or the uses of non-active polymeric paints acting solely as a physical barrier preventing the diffusion of ions through to the metal surface. However ideas have recently come forward regarding the use of conductive and electro-active polymers. Theorised to not only prevent the diffusions of ions on a physical level but to also act as an electrochemical barrier by passivating the surface of the metal so that it can protect itself from further degradation caused by corrosive agents, one such polymer that has been put forward is Polyaniline (PANI). Through the process of doping, PANI can be made to conduct an electrical current through the formation of charge carriers by oxidising the PANI with a protonic acid which can be functionalised. Further investigation has found that the functionalisation of these acids can dramatically change the once insoluble material in common solvents soluble, increasing the processability and possible increase the applications of this materials.
This thesis reports the synthetic routes used to obtain functionalised Sulphonic acids based on the precursor 5-Sulphoisophthalic acid by acid catalysed esterification’s are described. With the synthesis phosphoric acid diester carried out by several named reported methods and both series were progressed forward to dope PANI (polyaniline). The optical properties were analysed for all doped PANI in DCM showing that branched side chains produced the highest optical absorption at around 944 nm and some as thin films (21) and (25), showing optical band gaps of 1.21 eV.
This thesis also reports the anti-corrosions properties for the doped PANI systems. Films were cast coating mild carbon steel and copper plates, along with a range of acrylic resin/doped PANI composite films, PVC/doped PANI composite films and a set of films for an epoxide resin/doped PANI (17) composite. Samples were subjected to accelerated corrosion tests and showed that the application of PANI to the metal surfaces was beneficial and displayed efficacious anti-corrosion properties, not only in the doped state (emeraldine salt) but also in its native undoped state (emeraldine base) where the polymer undergoes redox reactions at the metal interface passivating the surface and creating an electrochemical barrier system which the polymer itself is a component however corrosion inhibition is only truly effective when a physical barrier is used in combination.
The results of the dopant synthesis, doped PANI systems and their composites in resins and the data from NMR spectroscopy, IR, elemental analysis, LC-Mass spectroscopy, mass spectroscopy, UV-Vis spectroscopy are presented in this thesis. The accelerated corrosion tests and the data from scanning electron microscopy (SEM) are also presented within this thesis.