Synthesis of highly refractive poly(phenylene thioether)s containing a binaphthyl or diphenylfluorene unit

Abstract

High refractive index poly(phenylene thioether)s (PPTs) with good solubilities were developed by introducing binaphthyl or diphenylfluorene units. They were prepared by the polycondensation of dithiols, 2,7-thianthrenedithiol and 9,9-bis(4-sulfanylphenyl)fluorene, with difluoro compounds, 4,4′-difluoro-1,1′-binaphthyl and 2,7-difluorothianthrene. The bulky and non-planar structures of the PPTs endow good solubilities in several organic solvents, such as 1,1,2,2-tetrachloroethane (TCE), N-methylpyrrolidone (NMP), and N,N′-dimethylpropyleneurea (DMPU). They exhibit a high thermal stability, that is, 5% weight loss temperatures of 483 and 494 °C under nitrogen, and glass transition temperatures of 235 and 237 °C, respectively, reflecting the rigid structures of the diphenylfluorene or binaphthyl unit. They also exhibit a good transparency in the visible region (transmittance > 85% at 400 nm) and high refractive indices of 1.776 and 1.737, and low birefringences of 0.0049 and 0.0035, respectively. The PPTs with a high thermal stability and good optical properties should be good candidates for optical applications.