Highly transparent and photopatternable spirobifluorene-based polythioethers with high refractive indices via thiol-ene click chemistry

Abstract

A series of polythioethers with spirobifluorene skeletons was successfully synthesized by a thiol-ene reaction. A spirobifluorene-containing diacrylate (2,2′-diacryloyloxy-9,9′-spirobifluorene, DASF) was designed and reacted with dithiol components to prepare high-refractive-index polymers (1.7169–1.6690) with high transparency (>90% at 400 nm). The poly(phenylene thioether) obtained from DASF with 1,5-naphthalenedithiol exhibited the highest refractive index (1.7169) and a low Abbe number (14.3), while the polymer obtained with 1,3-benzenedithiol showed a high refractive index (1.7112) and a relatively high Abbe number (19.6). The resulting spirobifluorene-containing polythioethers exhibited tunable glass transition temperatures (Tg = 90–164 °C), and high thermal stabilities (Td5 = 297–353 °C). UV nanoimprinting lithography using rapid thiol-ene photopolymerization of DASF with 1,6-hexanedithiol enabled the successful formation of high-refractive-index polymer nanoimprinted patterns. The presented design strategy allows manipulation of the refractive index and Abbe number, as well as the ability to design molecular structures with suitable aromatic and aliphatic chains between the spirobifluorene units, thus helping to achieve high transparency, flexibility, and thermal stability, in addition to excellent light-induced processability for nano- and microfabrication.