Low-Refractive-Index Deep-Ultraviolet Transparent Poly(fluoroalkyl-co-methylsilsesquioxane) Resins Synthesized by Cosolvent-Free Hydrolytic Polycondensation of Organotrimethoxysilanes.

Cosolvent-free (solventless) hydrolytic polycondensation of fluoroalkyltrimethoxysilanes of linear fluoroalkyl groups of the form R = CnF2n+1C2H4 (n = 1, 4, and 8) and methyltrimethoxysilane followed by thermal curing yielded dense polymeric silsesquioxane (SQ) resins with low refractive indices and deep-ultraviolet transparency with an ultraviolet absorption edge at ∼210 nm. The refractive index at 589 nm was adjustable at ∼1.35-1.39, and the lowest value was ∼1.354 for the stiff resin and ∼1.347 for the soft resin of poly(R-co-Me-SQ) prepared at n = 8. The refractive indices of these resins were consistent with the linear combinations of molar refractivities of constituent functional groups, and there were no free-volume anomalies.