The comonomer units can in particular be vinyl esters, such as vinyl acetate, vinyl alcohol, esters of olefinically unsaturated carboxylic acids of 3 to 5 carbon atoms (in the acid part) and of 1 to 17 carbon atoms in the alcohol part of the ester, for example diethyl maleate, n-butyl acrylate or 2-ethylhexyl methacrylate, and also the said acids themselves.