Organosilanols typically show a high condensation tendency and only exist as stable isolable molecules under very specific steric and electronic conditions at the silicon atom. In the present work, various novel representatives of this class of compounds were synthesized by hydrolysis of alkoxy‐ or chlorosilanes. Phenyl, 1‐naphthyl, and 9‐phenanthrenyl substituents at the silicon atom were applied to systematically study the influence of the aromatic substituents on the structure and reactivity of the compounds. Chemical shifts in 29Si NMR spectroscopy in solution, correlated well with the expected electronic situation induced by the substitution pattern on the Si atom. 1H NMR studies allowed the detection of strong intermolecular hydrogen bonds. Single‐crystal X‐ray structures of the alkoxides and the chlorosilanes are dominated by π‐π interactions of the aromatic systems, which are substituted by strong hydrogen bonding interactions representing various structural motifs in the respective silanol structures.

No abstract

High-refractive-index polysiloxanes containing naphthyl, phenanthrenyl, phenyl, and methyl groups have been synthesized using a polycondensation reaction starting from substituted di- and trialkoxysilanes. The obtained polymers comprised linear siloxane and partially cross-linked silsesquioxane units and showed optical transparencies of up to 99% at a thickness around 120 μm and high refractive indices of up to 1.622. The polymeric structures contained stabilized silanol groups that were further cross-linked at increased temperatures of 200 °C resulting in the formation of hybrid inorganic–organic resins. These typical thermal treatments at 200 °C for 72 h kept the transparencies as high as 98% and slightly lowered the RIs to values up to 1.610. A detailed structure evaluation of the resulting systems showed, depending on the size of the polycyclic aromatic substituent, excimer formation, which is based on weak interactions of the aromatic groups in the polymeric material. After thermal consolidation, glass-transition temperatures of the cross-linked systems were in the range of 18–74 °C depending on the composition. Thermal stabilities of the final resins reached higher values than commonly used siloxane resins up to 470 °C. The final materials are potential resins for high-temperature optical applications.