Two unsaturated polyesters containing a halogen (bromine) in the backbone of the polymer chain were synthesized and compared with a halogen-free polyester. The bromine content was measured by elemental analysis. The chemical structures of the polyesters were characterized by means of IR and H-1-NMR spectroscopies. Feldspar was used as the filler to form the polyester composites. The effects of the halogen substituents, filler concentration, and crosslinking monomers and comonomers on the electrical and mechanical properties of the polyester composites were studied. The flammability was also investigated. The styrenated polyesters and their composites achieved fire resistance and good mechanical and electrical properties. (c) 2006 Wiley Periodicals, Inc.