Terpolymers based on .alpha.,.beta.-unsaturated dicarboxylic anhydrides, .alpha.,.beta.-unsaturated compounds and polyoxyalkylene ethers of lower unsaturated alcohols

A copolymer based on .alpha.,.beta.-unsaturated dicarboxylic anhydrides, .alpha.,.beta.-unsaturated compounds and polyoxyalkylene ethers of lower unsaturated alcohols, which comprises components

• a) 20-80 mol % of bivalent structural units A ##STR12## where R.sup.1 and R.sup.2 are, independently of one another, hydrogen or methyl,
• a and b are zero or one and a+b is one,
• X and Y are identical or different and are the --N--HR.sup.3 group,
• where R.sup.3 is C.sub.6 -C.sub.40 -alkyl, C.sub.5 -C.sub.20 -cycloalkyl or C.sub.6 -C.sub.18 -aryl, the --N--(R.sup.3).sub.2 group,
• where R.sup.3 is identical or different and is as defined above, and/or
• the --O--R.sup.4 group,
• where R.sup.4 is hydrogen, a cation of the formula H.sub.2 N.sup..sym. (R.sup.-3).sub.2 or H.sub.3 N.sup..sym. R.sup.3, C.sub.6 -C.sub.40 -alkyl, C.sub.5 -C.sub.20 -cycloalkyl or C.sub.6 -C.sub.18 -aryl,
• b) 19-80 mol % of bivalent structural units D ##STR13## in which R.sup.5 is hydrogen or C.sub.1 -C.sub.4 -alkyl and
• R.sup.6 is C.sub.6 -C.sub.60 -alkyl or C.sub.6 -C.sub.18 -aryl, and
• c) 1-30 mol % of bivalent structural units E ##STR14## in which R.sup.7 is hydrogen or methyl,
• R.sup.8 is hydrogen or C.sub.1 -C.sub.4 -alkyl,
• Z is C.sub.1 -C.sub.4 -alkylene
• m is a number from 1 to 100,
• R.sup.9 is C.sub.1 -C.sub.24 -alkyl, C.sub.5 -C.sub.20 -cycloalkyl, C.sub.6 -C.sub.18 -aryl or --C(O)--R.sup.10, where
• R.sup.10 is C.sub.1 -C.sub.40 -alkyl, C.sub.5 -C.sub.10 -cycloalkyl or C.sub.6 -C.sub.18 -aryl.