Abstract: A polyurethane corresponding to the formula: ##STR1## wherein Q is a divalent, mononuclear or dinuclear aromatic radial which is unsubstituted or is substituted by lower alkyl groups and which can contain, as a linking member, a lower alkylene group,X is one of the groups --O--Ph--Z--Ph--O-- and --OOC--(CH.sub.2).sub.y --COO--,Ph being an optionally substituted phenylene group,Z being an alkylene group having 1-4 carbon atoms and y being a number from 2 to 12,R is a hydrogen atom or a methyl group,Y is an alkylene radical having 2-6 carbon atoms,m is an integer from 4 to 50n is an integer from 1 to 6 ando is an integer from 4 to 20having the properties of thermoplasts and being hardenable to give elastic products. It is suitable for use as a hardenable constituent of photopolymerizable materials.

Abstract: An electrophotographic copying process is disclosed comprising the steps of performing a cleaning operation on a recording element by carrying out at least one rinsing operation of the element utilizing a first quantity of a developer liquid; performing a series of copying cycles comprising charging, exposing, developing with a liquid developer, transferring and fixing; and intermittently performing additional cleaning operations independently of each cycle of the series of copying cycles using a quantity of developer liquid which is at most as great as the first quantity.