The Mass Transfer and Charge Transport Properties of Osmium bis(2,2’-bipyridyl)- containing 4-Vinylpyridine / Styrene Copolymers. In Chapter 1, some of the techniques used for the characterisation of the electrochemical properties of electrode modifying materials are introduced. A brief review of the mass transfer and charge transport studies of redox materials is presented. In Chapter 2, the admittance characteristics of crystal coatings are studied. This analysis allows the rigidity and resident layer mass of the coatings to be probed as a function of the electrolyte type and concentration. In Chapter 3, the charge transport properties of [Os(bipy)2(PVPx)ioCl]+ , where x signifies the percentage of poly 4-vinylpyridine in the poly 4-vinylpyridine/styrene copolymer backbone, are probed as a function of the electrolyte type and concentration. Activation parameters are evaluated to aid diagnosis of the rate determining steps. The remainder of the thesis deals with the mass transfer properties of the highest and lowest styrene content metallopolymers. In Chapters 4 and 5, the redoxswitching- induced mass changes of [Os(bipy)2(PVP33)ioCl]+ coated crystals are investigated as a function of the HCIO4 and UCIO4 concentration of the contacting electrolyte and the experimental timescale using the Electrochemical Quartz Crystal Microbalance (EQCM). Comparison with [Os(bipy)2(PVPioo)ioCl]+ is made and a relationship between the ease of solvent transfer and the rate of charge transport is suggested. In Chapter 6 , the effect of acetonitrile on the mass transfer and charge transport properties of [Os(bipy)2(PVPioo)ioCl]+ crystal coatings is investigated. The relationship between the degree of polymer swelling, the ease of mass transfer and the rate of charge transport is illustrated.