Amphiphilic ionic liquids as catalysts for efficient synthesis of novel isosorbide-based optical polymers with good biocompatibility and tunable properties

Abstract

Accurate design and green synthesis of sustainable optical materials from renewable biomass has become vital in polymer science, especially in field of corneal contact lenses or intraocular lens (IOLs). Here we demonstrate the structure design of monomers and efficient synthesis of novel optical poly(isosorbide thioethers) (PITEs) with methyl, alicyclic or aromatic side-groups for high-performance biomedical optical materials. To regulate and control the polymerization process accurately, ionic liquids (ILs) were selected as catalysts and evaluated systematically. Since the presence of hydroxyl in anion improved proton-accepting ability combined with cations functionalized with dual activation sites, the IL tetraethylammonium lactate [TEA][Lac] in trace amount was discovered to show outstanding catalytic performance, better than the reported catalysts. According to experimental results, NMR analysis and DFT calculations, the anion-cation synergistic catalytic mechanism for nucleophilic hydrothiolation was proposed at molecular level. The activation barriers of transition structures decreased significantly from 211.1 to 16.7 kJ·mol−1 after using IL catalyst. The novel PITEs exhibited excellent biocompatibility for L929 cells, good optical transparency (>90 %) and higher refractive index (nD = 1.57 ∼ 1.61) than commercial IOLs (nD = 1.46 ∼ 1.55). Meanwhile, the PITEs possessed not only tunable mechanical properties (strain at break of 1.6 %∼367 %, storage modulus of 2.5 ∼ 4.3 GPa), but also suitable glass-transition temperature (Tg = 41.6 ∼ 92.9 °C) and good thermal stability for polymer melting or moulding process. This work provides a versatile approach for convenient fabrication of novel isosorbide-based polymers with adjustable properties for biomedical optical lenses, which are promising to achieve scale-up and application in future.