Sulfur-Based Polymer Synthesis for High Refractive Index Optical Materials with Low Birefringence

High refractive index polymers are an emerging class of transprent materials for a wide range of applications. Increasing the refractive index of these materials, however, often leads to higher birefringence and optical dispersion. In this presentation, we describe two sulfur-based polymer design strategies that address this trade-off through controlled molecular architecture. First, sulfur-rich aliphatic thermosets were prepared from episulfide, polysulfide, and elemental sulfur components, affording transparent materials with tunable refractive index, low dispersion, and low birefringence without relying on aromatic structures. Second, a modular fluorene cardo platform bearing sulfur-containing aromatic substituents was developed for thermoplastic high-index polymers. By introducing polymerizable groups at the 2,7-positions, the cardo motif was incorporated into polyesters, poly(arylene ether)s, and poly(arylene thioether)s using multiple polymerization methods. Together, these studies demonstrate how sulfur chemistry and polymer architecture can be combined to achieve high refractive index while suppressing optical anisotropy.