Novel Organosilanes for the Preparation of High Refractive Index Silicone Coatings

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Novel Organosilanes for the Preparation of High Refractive Index Silicone Coatings Pierre M. Chevalier and Duan L. Ou Dow Corning S.A., Surface and Interface Solutions Center (SISC) Rue Jules Bordet, Parc Industriel Zone C, 7180 Seneffe, Belgium ABSTRACT Synthetic routes to high refractive index curable polyaromatics and halogenated aromatic functional silicone resins were developed. Organo silanes containing anthracenylmethyl-, naphthylmethyl- and iodobenzyl- groups were synthesized and used as precursors for the preparation of stable and soluble aryl-functional silicone resins. Alternatively the direct iodination of pre-formed aromatic-functional resins was investigated. We demonstrated the preparation of coatings with RI as high as 1.770 at 633 nm representing a significant optical enhancement as compared to traditional silicone and organic coatings.

INTRODUCTION High RI materials find application in optics e.g. antireflective coatings for display devices, intra-ocular and optical lenses [1], optical amplifying fibers, and high RI adhesives or for cosmetic application [2]. Two major approaches have been reported to enhance RI of silicone polymers, organic resins and glasses. The first approach involves blending of silica and organopolysiloxane with “RI enhancers” e.g. titania [3]. However, the RI of the final inorganic material is often much lower than the theoretical expected value because of in-homogeneity in the dispersion of the oxides particles [4]. In addition, brittle glass or co-inorganic material does not always fulfill the processability and mechanical requirements of specific applications. The second approach, focusing on the preparation of phenyl versus alkyl-containing silicones, allows tunable RI from 1.43 to 1.55, confirming the importance of the organic group contribution onto the RI. Similarly, acrylic, phenolic, epoxy and polyester resins are prepared partially using halogenated aromatic functional monomers [5] to enhance RI in the low range of 1.56 to 1.63. However, these organic resins do not always exhibit good mechanical, thermal properties and chemical resistance. Subsequently, a need still remains for high RI stable, curable and easily processable organo-modified silicone resins versus glasses or mixed metal oxides, having chemical resistance and well-balanced thermomechanical properties versus organic resins. In the present study, we have investigated the preparation of high RI silicone resins, above 1.56 being the upper limit for phenyl resin, containing RI enhancing organic groups.

EXPERIMENTAL DETAILS All reactions were carried out in air or nitrogen in anhydrous solvents. Spectroscopic characterization was performed on a JEOL Lambda 400 MHz NMR. Resin thin films (1,500

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to 10,000 Å) prepared by spin-coating on silicon wafers were further cured below 250OC for RI evaluation by spectroscopic ellipsometry on a J.A. Woollam M-88 SE or VASE (633 nm). Preparation of high RI fused-rings aromatic silsesquioxane resins Tri-n-propylamine was added to chloromethylanthracene