Molecular Engineering of Heterofunctional-Oligosiloxane-Modified Vi-POSS via Piers-Rubinsztajn Reaction for Reinforcement in Transparent Silicone Elastomers

To address the challenge of simultaneously enhancing the mechanical properties of addition-type liquid silicone rubber (ALSR) while maintaining excellent optical transparency, we report the design and synthesis of a novel liquid vinyl-functionalized POSS (Vi-POSS) via the Piers-Rubinsztajn reaction between SiH-containing Q-type POSS (H-POSS) and a heterofunctional oligosiloxane. This strategy enables precise modulation of cross-linking networks while improving filler–matrix compatibility through covalent bonding. The molecular structure of Vi-POSS was confirmed by 1H/29Si NMR and FT-IR spectroscopy, revealing complete vinyl functionalization. A series of ALSRs were prepared using Vi-POSS as both reinforcing filler and cross-linker. Systematic investigations demonstrated that optimal incorporation of 4 wt % Vi-POSS yielded exceptional thermomechanical performance: a 641% increase in tensile strength (2.52 MPa) and 322% enhancement in elongation at break (243.15%) compared to pristine ALSR, while maintaining 90% UV–vis transmittance across the visible spectrum. Thermal stability analysis revealed that with the incorporation of 6 wt % Vi-POSS, compared with the pristine ALSR, the initial decomposition temperature (T10%) and maximum degradation temperature (Tmax) increased by 20 and 12 °C, respectively. Additionally, the char residue at 800 °C was enhanced. Microstructural characterization via SEM confirmed the homogeneous dispersion of Vi-POSS without microphase separation, indicating an excellent interfacial compatibility and superior dispersion of Vi-POSS in the ALSR matrix. This work presents a paradigm shift in the design of transparent high-performance ALSR by integrating molecular-level structure control with nanoscale dispersion optimization. The demonstrated balance of mechanical robustness, thermal stability, and optical clarity positions these materials as promising candidates for advanced applications in flexible optoelectronics, transparent electronics, and biomedical devices requiring simultaneous load-bearing and optical functionality.