Incorporating Pendent Fullerenes with High Refractive Index Backbones: A Conjunction Effect Method for High Refractive Index Polymers

To achieve high refractive index polymers (HRIPs), we report here the design and synthesis of four fullerene polyesters (P1–P4), based on the conjunction effect from the high refractive index polyester backbones and pendent fullerene side chains. At sodium D line (589 nm), the refractive indices of the fullerene polyesters are all higher than 1.80, the used believed upper limitation of intrinsic organic polymers. To achieve precise pendent fullerene structure, these polyesters were synthesized via condensation polymerization by a fullerene diol with different aromatic diacyl chlorides, where the diacyl chlorides with high molar refraction increment value moiety were selected by molecular tailoring according to Lorentz–Lorenz equation. The fullerene polyesters are characterized by gel permeation chromatography (GPC), ultraviolet–visible (UV–vis) spectroscopy, and the molecular weights are obtained by a quantitative NMR technique with end-group estimation. The formation of fullerene polyesters is also proved by the 1H DOSY NMR results. These fullerene polyesters have good solubility in some common organic solvents, good thermal stability up to 320 °C, and film forming ability. All these films have good adhesion to glass sheets with relatively good hardness. Among them, the thiophene-containing fullerene polyesters (P1) has the best optical properties, with the highest refractive index value (1.86 at 589 nm), one of the highest value for intrinsic organic polymers, and the highest Abbe number (27.9).