Tailoring High Refractive Index and High Abbe Numbers in Polymers via a Biomass-Derived Thiadiazole Platform

High refractive index polymers (HRIPs) have emerged as a research focus in the development of advanced optical materials and devices. This work develops a series of thiadiazole-based polymers that exhibit high refractive indices (nD = 1.61∼1.68) and satisfactory Abbe numbers (νD = 24∼46), with favorable mechanical and thermal properties. These polymers are constructed from mercaptans and biobased monomers having a thiadiazole group through a photoclick thiol–ene reaction. The optical properties of the polymers can be effectively changed by regulating the chemical structures of the monomers. For example, monomers with methoxy substituents give polymers possessing a high Abbe number but slightly low nD. On the other hand, curing groups with shorter chain lengths such as vinyl groups exhibit higher nD than those of allyl and propenyl groups with longer chain lengths. Such variations of optical properties, depending on the substituents and curing groups of the monomers, are attributed to the density of chain packing in the polymers. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations are also employed for the investigation of the polarizability and molecular packing type of the polymers.