Synthesis of novel sustainable optical poly(isosorbide thioethers) with high refractive index and good biocompatibility by functional ionic liquid catalysts

Abstract

The synthesis of intraocular lenses (IOLs) with high refractive index (RI) and good transparency to create patient-specific eye power is of primary importance, while the development of a novel IOL material especially with outstanding optical characteristic and biocompatibility is still an ongoing challenge. Herein, bio-based poly(isosorbide thioether) (PITE) with excellent optical properties was developed as a novel IOL material and a new strategy for synthesizing high molecular weight PITE using ionic liquid catalysts was proposed. Compared to traditional IOLs (RI= 1.45–1.54), the synthesized bio-based PITEs showed the highest RI of 1.64 and optical transparency of 93%, indicating that they were indicative of excellent optical materials. Furthermore, the resultant PITEs also exhibited ideal glass transition temperatures (T_g = 7.5–50.9 °C) , good thermal stability (T_d-5% ˃ 312 °C) and excellent biocompatibility for L929 and HeLa cells. In order to achieve efficient synthesis of PITE, a series of functional ionic liquid catalysts were designed and synthesized. Among them, 1,8-diazabicyclo[5.4.0]-undec-7-en-8-ium lactate ([DBU][Lac]) in a trace amount exhibited highest catalytic performance, presenting the Mw up to 63.3 kg·mol^-1, superior than 7.4 kg·mol^-1 without a IL. Detailed mechanistic investigations using nuclear magnetic resonance spectroscopy and density functional theory calculation revealed that the “amphiphilic” character of ILs showed cation–anion synergistic catalytic mechanism and then promoted the nucleophilic hydrothiolation. The present study could provide enormous opportunities in the design and synthesis of bio-based optical polymers with high performance for IOLs, corneal contact lenses or other optical uses.