Silica-based hybrid materials formed by surface grafting with necklace polymers containing POSS–DMS structures

Abstract

As organic–inorganic hybrids, necklace-type PDMS–POSS polymers were grafted onto silica particles and synthesized via a two-step ring-opening equilibrium polymerization of cyclic siloxane (D₄) and bifunctional POSS. The polymers were then grafted on silica particles of different sizes (100-nm hollow particles; and 200- and 500-nm solid particles) to fabricate POSS–DMS-grafted silica composites. The materials were characterized using ¹H-NMR and ²⁹Si-NMR spectroscopy to confirm the polymer structures and the degree of grafting. Thermogravimetric analysis was used to evaluate the thermal stability and quantify the grafted organic content. The results demonstrated that the grafting efficiency and thermal properties were influenced by both the average siloxane chain length and the surface area of the silica particles. The ungrafted POSS–DMS polymers showed the highest thermal stability (T_d,5% > 470 °C) at an average siloxane chain length of 3–4, indicating an optimal balance between POSS rigidity and siloxane flexibility. By contrast, the grafted silica samples exhibited a nearly constant T_d,5% of approximately 460 °C, regardless of chain length. This indicates that grafting onto the silica surface restricts chain mobility and suppresses chain length-dependent thermal behavior.