Abstract: Polymers having a molecular weight (weight average) M.sub.w from 10.sup.3 to 10.sup.6, comprising recurring structural units of the formulae (I), (IIa) and (IIb) ##STR1## in which R.sub.1 is hydrogen or methyl, Y is a direct bond or a divalent radical of the formula (III) ##STR2## in which Z is a C.sub.1 -C.sub.6 alkylene group bound to the phenyl nucleus,OR.sub.2 is an acid-cleavable radical,in which R.sub.2 is C.sub.4 -C.sub.10 tert-alkyl, allyl, cyclohex-2-enyl, C.sub.6 -C.sub.14 aryl or C.sub.7 -C.sub.16 aralkyl which are unsubstituted or mono- or poly-substituted by C.sub.1 -C.sub.6 alkyl groups, C.sub.1 -C.sub.6 alkoxy groups or halogen atoms, trialkylsilyl or a group of the formulae (IV)-(VII) ##STR3## in which R.sub.8 is C.sub.1 -C.sub.6 alkyl, or C.sub.6 -C.sub.14 aryl or C.sub.7 -C.sub.16 aralkyl which are unsubstituted or mono- or poly-substituted by C.sub.1 -C.sub.6 alkyl groups, C.sub.1 -C.sub.6 alkoxy groups or halogen atoms,R.sub.3 and R.sub.4 independently of one another are hydrogen, C.sub.