Abstract: A secondary stabilizer for emulsion polymers is disclosed. The secondary stabilizer is a polyester containing diol residues, residues of olefinically unsaturated dicarboxylic acids which carry sulfonate groups and residues of dicarboxylic acids which do not contain olefinic unsaturation or sulfonate groups. The residues of the olefinically unsaturated dicarboxylic acids comprise from 70 mole-% to 99 mole-% of dicarboxylic acid residues in the polyester and from 1 mole-% to 30 mole-% of residues of dicarboxylic acids which do not contain olefinic unsaturation or sulfonate groups. The polyester secondary stabilizer is not a surfactant (does not significantly lower the surface tension of water) and in addition is biodegradable.