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 and in addition is biodegradable .