Polymaleic anhydride derivatives

A method for demulsifying a water-in-oil emulsion which comprises

• admixing an effective amount of the partial ester reaction product obtained by reacting a polymer or copolymer containing recurring structural units selected from the group consisting of ##STR6## or said copolymer which additionally contains recurring structural units ##STR7## where R represents a straight or branched alkyl having 4 to 14 carbon atoms, R.sup.1 and R.sup.2 are the same or different and represent a straight or branched chain alkyl having 1 to 12 carbon atoms, or R.sup.1 and R.sup.2 together with the nitrogen atom to which they are attached form a 5- or 6-membered heterocyclic ring which is pyrrolidine, piperidine or morpholine,
• or said copolymer which additionally is a copolymer of maleic anhydride with one or more ethylenically unsaturated monomer selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, aconitic acid, ethyl acrylate, methyl methacrylate, ethyl crotonate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, dimethyl itaconate, acrylonitrile, acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, N-acrylamidoglycolic acid, vinyl acetate, vinyl sulfonic acid, allyl sulfonic acid, 4-styrenesulfonic acid, vinyl phosphonic acid, styrene phosphonic acid, allyl alcohol, allyl acetate, styrene, alpha-methylstyrene, ethylene, propylene, hexene, 2,4,4-trimethylpent-1-ene, N-acrylamidopropane sulfonic acid and mixtures thereof,
• with an alkoxylated alcohol of the formula ##STR8## where R.sup.3 is a straight or branched chain alkyl having 1 to 18 carbon atoms, R.sup.4 is hydrogen or methyl and n is an integer from 1 to 20;
• with an alkoxylated alkyl phenol of the formula ##STR9## wherein R.sup.4 is hydrogen or methyl, n is an integer from 1 to 20, R.sup.5 is a straight or branched chain alkyl having 1 to 12 carbon atoms and m is an integer from 1 to 3;
• with a polyalkylene glycol of the formula ##STR10## wherein R.sup.4 is hydrogen or methyl and p is an integer from 3 to 30;
• or
• with a mixture thereof,
• where from 25 to 75% of the acid or anhydride groups in the polymer or copolymer are esterified;
• into said emulsion with agitation, and then
• allowing the water and oil to separate upon standing.