Polyvinyl halide or polyvinyl graft copolymers intimately mixed with a polyester derived mainly from an halogenated bicycloheptene carboxylic acid or anhydride such as chlorendic acid or anhydride and an alkylene glycol or alkylene oxide such as ethylene oxide are provided. The graft copolymers of the invention are obtained by polymerizing a vinyl halide in bulk in contact with an olefin polymer. The graft copolymer compositions of the invention have good clarity and provide improved processing characteristics and increased impact strength without reduction in heat distortion resulting from the addition of the polyester. The improved impact strength polyvinyl halide compositions of the invention can include blends of the polyester of the invention with modifying compounds, such as alkyl methacrylate-butadiene/styrene graft polymer impact modifiers and halogenated polyvinyl chloride. Blends of vinyl halide polymers with the polyesters of the invention provide compositions having improved processability. A reduction in melt viscosity and fusion temperature can be obtained in the blends while maintaining or increasing heat distortion temperature. The compositions of the invention are useful in the production of molds made by extrusion, injection, blow, and sheet molding processes.