Synergistic Rigid-Flexible Cross-Linking via Thiol-Modified POSS for High-Performance Thermally Expandable Microspheres with Extended Foaming Range and Enhanced Expansion.

Thermally expandable microspheres (TEMs) are widely used as lightweight fillers and physical foaming agents. Commercial high-temperature TEMs suffer from pore collapse, low expansion ratio, and poor thermal stability. Based on thiol-ene click chemistry, we synthesized a thiol-functionalized 4-SH-POSS cross-linker with a three-dimensional rigid cage structure and flexible long chains, which was incorporated into acrylate copolymers via in situ polymerization to form C-S bond cross-linked networks in TEM shells. Using multiscale characterization techniques and interfacial migration analysis, we systematically investigated the regulatory role of 4-SH-POSS in the chemical structure, thermodynamic properties, and microstructure of TEMs. The results indicate that the modified TEMs exhibit optimal overall performance, achieving a maximum expansion temperature (Tmax) of 210 °C, an approximately 50% increase in expansion ratio, and a heat resistance time (HRT) extended to 10 min. Uniformly dispersed 4-SH-POSS enables synergism between rigid cages and flexible C-S bonds, enhancing stress dissipation and ductility. The compatibility of the cross-linker and foaming agent affects the interface migration and material properties. This work provides new strategies for high-performance TEMs, with promising applications in high-temperature lightweight materials.