The invention relates to a positive-working radiation-sensitive mixture and a copying material produced therefrom on a layer support. The mixture contains as essential constituents a 1,2-quinone diazide or a combination of:1) a compound forming strong acid when exposed to actinic radiation and2) a compound containing at least one acid-cleavable C--O--C bond,and a binder with repeating units of the general formula I ##STR1## wherein R.sub.1 denotes a hydrogen or halogen atom, or a cyanide or an alkyl group,R.sub.2, R.sub.3, R.sub.4 are identical or different and denote hydrogen, or alkyl or aryl groups,R.sub.5, R.sub.6 and optionally R.sub.7 are identical or different and denote hydrogen or halogen atoms, or alkyl, aryl or alkoxy groups, andX denotes the atoms necessary to complete a mononuclear or polynuclear carbocyclic aromatic ring system, andn is 1, 2 or 3.The mixture according to the invention yields lithographic printing plates with a high print run which can be thermally post-cured and have good resistance to chemicals, also photoresists with high heat resistance.