The Small Business Innovation Research (SBIR) project will develop toughened epoxy resin and hardener systems for fiber reinforced composites that are well suited for resin infusion processes such as Vacuum Assist Resin Transfer Molding (VARTM). The common use of carboxyl-terminated butadiene acrylonitrile rubbers to toughen epoxies results in relatively large elastomeric particles filtering out of the matrix during infusion and, thus, adversely affects rheology. In this project, nano scale particles based upon hyper-branched poly(siloxanes) for toughening epoxies will be developed. Through the use of these nano scale particles, resin fusion will be easily accomplished and the filtering out of the elastomeric particles will be avoided. The siloxane based nano particles are also expected to have improved thermal stability during curing. <br/><br/>Fiber reinforced composites are used in a wide range of high performance engineering applications requiring low weight and high strength. The composite industry is moving toward the VARTM process. These nano scale based epoxy resins will be low cost with improved mechanical and rheological properties compared to current resins. The use of high value epoxy resins in composites is projected to be 53,000 tons by 2012, and about 4 times this figure worldwide. The potential market for the resin alone will be approximately $200,000,000. The resin suppliers taking advantage of the VARTM process with nano particle toughened resins will have a competitive advantage in the supply of new resins suited for the manufacture of epoxy resins.