Additives for improving the cold properties of fuel oils

1. A terpolymer consisting of ethylene, propene,

i) from 4.0 to 12.0 mol % of structural units derived from at least one ethylenically unsaturated ester, wherein the at least one ethylenically unsaturated ester is selected from the group consisting of ethylenically unsaturated esters having a C 4 - to C 20 -alkyl radical, and

ii) up to 3 mol % of structural units derived from an ethylenically unsaturated ester with a short alkyl chain having from 1 to 3 carbon atoms

wherein the terpolymer contains from 0.5 to 4.0 methyl groups derived from propene per 100 aliphatic carbon atoms, and fewer than 8.0 methyl groups stemming from chain ends per 100 CH 2 groups.

2. The terpolymer as claimed in claim 1 , wherein the structural units derived from ethylenically unsaturated ester are between from 4.5 to 10 mol %.

3. The terpolymer as claimed in claim 1 , in which the ethylenically unsaturated ester is a vinyl ester of a carboxylic acid having from 5 to 21 carbon atoms.

4. The terpolymer of claim 1 , in which the methyl groups derived from propene ii) is between 0.6 and 4.0 per 100 aliphatic carbon atoms.

5. The terpolymer as claimed in claim 1 , in which the methyl groups stemming from chain ends is between 2.5 and 8.0 CH 3 /100 CH 2 groups.

6. The terpolymer of claim 1 , in which a sum G of molar content of said unsaturated ester i) and the number of methyl groups derived from propene per 100 aliphatic carbon atoms of the polymer ii), according to the formula

G =[mol % of unsaturated ester]+[propene-CH 3 ]

is between 5.5 and 11.0.

7. The terpolymer of claim 1 , in which the terpolymer has a weight-average molecular weight Mw determined by means of gel permeation chromatography against poly(styrene) standards of between 2500 and 50 000 g/mol.

8. An additive mixture comprising

A) at least one terpolymer of claim 1 , and

B) from 0.5 to 20 parts by weight, based on A), of at least one further component which is effective as a cold additive for mineral oils and is selected from the group consisting of

B1) a copolymer of ethylene and an olefinically unsaturated compound whose content of olefinically unsaturated compound is at least 2 mol % higher than the content of ethylenically unsaturated ester in the terpolymer A),

B2) a comb polymer, and

B3) mixtures of B1) and B2).

9. A process for improving the cold flowability of fuel oils by adding to the fuel oil at least one terpolymer of claim 1 .

10. A fuel oil comprising a middle distillate and at least one terpolymer as claimed in claim 1 .