Facile thiol-ene reactions of vinyl T₁₀/T₁₂ silsesquioxanes for controlled refractive indices for transparent fiber glass reinforced composites

Abstract

A series of thioether-functionalized silsesquioxanes (SQs) was synthesized by radically initiated thiol-ene reactions of vinyl T₁₀/T₁₂ SQ cages with a variety of commercially available thiols. The objectives of this study were to develop model reactions as the basis for using the vinyl T_10/12 compounds as novel crosslinking agents in the synthesis of new types of thiol-ene crosslinked polymers. A second motivation was to develop model compounds with controlled refractive indices and Abbe numbers as possibly modifiers of polymers used for a wide variety of optical and photonic applications. The reactions proceed under mild conditions over 24 h to give thioether SQs in high yields (>90%) and high purity without complex workup. The ease of synthesis coupled with the wide variety and availability of functionalized thiols provides a simple route to elaborating and functionalizing vinyl SQ cages. In addition, the resulting compounds exhibit refractive indices to 1.52 coupled with Abbe numbers to 51 due to the uniquely high electron density provided by the incorporated sulfur atoms, making them ideal compounds for use with optically transparent materials. In addition, cured forms of these compounds provide methods of raising the Abbe number of epoxy resins designed to index match fiberglass with the intent of making transparent fiberglass reinforced composites.