Polyester molding compositions

Abstract

Polyester molding compositions which contain an unsaturated polyester and an additional monomer for curing the polyester are improved by addition of a block copolymer which is modified with an unsaturated polyester. The block copolymer is an unsaturated block copolymer of a monoalkenyl aromatic hydrocarbon and a conjugated diene. The block copolymer is preferably produced by polymerizing styrene-butadiene diblock copolymer arms and coupling the arms with a difunctional coupling agent.

What is claimed is: 
     
       1. An improved polyester molding composition which contains an unsaturated polyester and an additional monomer for curing the polyester, the improvement comprising the addition of a low profile modifier which is produced by the process of free-radically grafting an unsaturated block copolymer with an unsaturated polyester in a solvent solution, the block copolymer consisting of at least one block of a monoalkenyl aromatic hydrocarbon and at least one block of a conjugated diene. 
     
     
       2. The molding composition of claim 1 wherein the block copolymer is grafted with the unsaturated polyester in solution with ortho-dichlorobenzene. 
     
     
       3. The molding composition of claim 2 wherein the unsaturated polyester which is grafted to the block copolymer is predominantly a propylene maleate polyester. 
     
     
       4. The molding composition of claim 1 wherein the monoalkenyl aromatic hydrocarbon is styrene and the conjugated diene is butadiene. 
     
     
       5. The molding composition of claim 4 wherein the block copolymer contains hydroxyl groups. 
     
     
       6. The molding composition of claim 4 wherein the block copolymer is an unsubstituted S--B--S block copolymer. 
     
     
       7. The molding composition of claim 6 wherein the low profile modifier is a blend of the grafted block copolymer and a non-grafted, unsubstituted S--B--S block copolymer. 
     
     
       8. The molding composition of claim 7 wherein the grafted and ungrafted block copolymers are produced by coupling living S--B arms with dibromoethane.