I'm searching for candidate polymers that possess very low refractive index (~1.3 - 1.35) in the visible portion of the spectrum.  Polymers that could be injection molded are preferred, but even relatively thin, solvent coatings may be acceptable.  Adhesion to other engineering optical plastics such as polycarb, acrylic/PMMA, polystyrene is also a consideration.  Transparency is pretty critical as well.