Novel phenolphthalein-based aromatic polyesters: The investigations of the relationships between refractive index and structure

Abstract

Aromatic polyesters are an attractive class of engineering thermoplastics with excellent chemical properties, thermal stability and environmental stability, as well as good optical properties, but they have rarely been reported. Refractive index (RI) is one of the properties commonly used to compare the optical properties of materials. The higher the refractive index, the thinner the lens made of the corresponding material; however, the preparation of high-refractive-index polymers is currently a thorny issue, in which the structure of the polymer molecules has a great impact on their refractive index, to design high-refractive-index materials requires starting from the structure of the molecules. Phenolphthalein has a unique structure with a molecular skeleton consisting of three benzene rings and a cyclic lactone that exhibits a twisted non-coplanar structure. This cyclic side group can hinder the accumulation between the polymer molecular chains, not only improving the solubility of the polymer molecules, but also increasing the transparency of the polymer films. In this work, we used phenolphthalein (PHT) and its derivatives to polymerize with terephthaloyl chloride (TPC), respectively, through the structural differences between them, the influence of polymer structure on the refractive index and thermal properties was discussed. Among them, polyester PAR-NPHT had the highest refractive index (n_d>1.67), and is expected to be a new generation of optical materials.

Graphical Abstract