From Polyimide to Polythioimide: A Silicon Etherification-Mediated Sulfur–Oxygen Exchange Pathway

This study presents a novel synthesis of high-molecular-weight polythioimides (PTIs) via a silicon etherification-assisted, homogeneous sulfur–oxygen exchange reaction. By incorporating tailored silane side chains, we precisely modulate polymer solubility, overcoming inherent heterogeneity to achieve quantitative conversion from polyimide precursors. The resultant PTIs demonstrate a remarkable combination of high refractive index (up to 1.67), low birefringence (0.0043), excellent thermo-mechanical properties (Tg ∼ 292.6 °C), and robust film-forming processability. Beyond their outstanding optical and physical characteristics, these materials exhibit exceptional functionality as selective adsorbents for noble metals, showing superior affinity for Pd2+ (91.1% selectivity in mixed ion systems) over common metal ions, governed by the soft–soft interaction principle. More significantly, we unveil a unique adsorptive-reductive synergy: PTIs serve as sacrificial reductants, coordinating and reducing noble metal ions to their zerovalent state while undergoing concurrent structural evolution. This work establishes a versatile platform for fabricating processable PTIs and reveals their dual utility in advanced optical materials and sustainable noble metal recovery, opening new frontiers for sulfur-containing polymers in high-tech technologies.