and polyethylene it has been found desirable to polymerise the monomers in situ when using absorbent supports such as paper however it can be desirable to form a partial prepolymer in order to ensure that the coating has a suitable viscosity at the time of application to the support coatings formed by the complete curing of a partial prepolymer in situ on a substrate gives improved imaging compared with the in situ polymerisation of the monomer or monomers from which the prepolymer was formed with the polyvinylcarbazoles particularly n vinylcarbazoles thermal uv and radiation induced methods can be used for grafting the radiation induced methods have been the most successful of the two radiation induced techniques the uv procedure appears to be the most useful presumably because surface grafting occurs predominantly if a solvent is required for the process with these monomers pyridine benzine u03b1 u03b2 and u03b3 picolines dimethylformamide nitrobenzene pyrrolidine tetrahydropyridine piperidine tetrahydrofuran 1 2 dichloroethane and chlorobenzene may be used however pyridine the u03b1 and u03b3 picolines and benzene are preferred a further aspect of the present invention is that both the photoconductive dark current ratios and the 34 imaging 34 property can be enhanced by the addition of additives capable of forming charge transfer complexes before during or after the grafting reaction these additives include the mineral acids such as sulphuric hydrochloric perchloric and to a lesser extent nitric acids salts of cadmium mercury and zinc particularly the chlorides and sulphates when soluble are also useful additives to achieve imaging the monomer of prepolymer is most preferably applied in a single coat if successive coats are applied the upper coats appear to leak away the images the coat is preferably of a thickness of from.