Organofunctional polysiloxanes for modifying the surface of finely divided particles

A coating material for modifying a surface of a finely divided pigment, filler or glass fiber wherein the coating material comprises a polyorganosiloxane with ester groups, epoxide groups or both linked to silicon atoms over carbon atoms and having a general formula ##STR9## wherein R.sup.1 is an alkyl group with 1 to 18 carbon atoms, at least 90% of the R.sup.1 groups being CH.sub.3 groups;

• R.sup.2 to the extent of 50 to 99% is identical with the R.sup.1 groups and, to the extent of 1 to 50%, is identical with the R.sup.3 and R.sup.4 groups;
• R.sup.3 is a group of the formula --(CH.sub.2).sub.n --CO--OR.sup.5, and/or ##STR10## and/or ##STR11## R.sup.5 is an alkyl group with 1 to 4 carbon atoms;
• n is a number from 3 to 20;
• R.sup.4 is a group of formula ##STR12## the ratio of R.sup.3 groups to R.sup.4 groups being 1:25 to 10:1, with the proviso that there must be at least one R.sup.3 group and at least one R.sup.4 in the average molecule;
• a is a number from 1 to 500;
• and
• b is a number from 0 to 10.