High refractive index polymers (HRIPs) serve as cutting-edge materials for lightweight, miniaturized, and high-resolution optical devices, although balancing ultrahigh refractive index, transparency, and thermostability remains challenging. Here, poly(dithioacetal)s with aromatic main chains, heavy and polarizable iodine groups, and additionally incorporated hydroxy units exhibit a high glass transition temperature (Tg = 112 °C) and an ultrahigh refractive index (nD = 1.81), while maintaining visible-light transparency (%T ≥ 96 at 1 μm thickness). Density measurements confirmed that the synergistic incorporation of iodine atoms and hydrogen bonds provides both a high packing coefficient and high polarizability, resulting in the formation of dense PDTA networks that simultaneously enhance nD and Tg. These findings rationalize a simple yet effective design for HRIPs to balance high thermostability and ultrahigh refractive indices without compromising transparency, through maximizing the polarizability density of repeating units.
Watanabe et al. (Thu,) studied this question.