1,2-Dithiolane/yne photopolymerizations to generate high refractive index polymers†

Abstract

Copolymerization and conjugate addition of disulfides generally and dithiolanes particularly have been reported for various applications. Here, a new framework for preparing high refractive index polymeric materials through the photoinitiated addition of methyl ester of lipoic acid (LipOMe) or methyl 4-methyl-1,2-dithiolane-4-carboxylate (Me-AspOMe) with various alkynes is explored, and an infrared spectroscopy methodology was developed for understanding the dithiolane homopolymerization kinetics. The effects of the 1,2-dithiolane and alkyne chemical structures on reaction rates, polymer structures, and optical properties of the synthesized polymers were examined. Characterization of the photopolymerization products showed significant dependence on the specific structure of the 1,2-dithiolane and alkyne reactants. The ability of the 1,2-dithiolane/alkyne reaction to introduce a large amount of sulfide linkages resulted in differences in the polymer refractive index relative to that of the unreacted materials, reaching values up to 0.07. Furthermore, the application of these 1,2-dithiolane-alkyne systems into two-stage photopolymeric holography materials in a two-dimensional, high-refractive index structure was demonstrated.