Modified copolymers which are suitable as paraffin dispersants and are obtainable by reacting a copolymer of an ethylenically unsaturated dicarboxylic acid and/or a dicarboxylic acid derivative and a diketene of the general formula I ##STR1## where R.sup.1 and R.sup.2, independently of one another, are each hydrogen or C.sub.1 -C.sub.30 -alkyl, with an amine of the general formula II ##STR2## where m may be from 0 to 100, n from 0 to 5 and x from 0 to 5, R.sup.3, R.sup.4 and R.sup.5, independently of one another, are each hydrogen or C.sub.1 -C.sub.5 -alkyl and A is NR.sup.6 R.sup.7 or C.sub.2 -C.sub.30 -alkoxy, and at least one of the substituents R.sup.6 or R.sup.7 is not hydrogen and is C.sub.1 -C.sub.30 -alkyl or alkenyl or a polyether radical ##STR3## where R.sup.8 and R.sup.9 are each hydrogen or C.sub.1 -C.sub.5 -alkyl and p is from 1 to 100, with the proviso that, when n is 0, A is NR.sup.6 R.sup.7, their preparation and use, and mineral oil middle distillates which contain these modified copolymers.