Octa(3,3,3-Trifluoropropyl) Polyhedral Oligomeric Silsesquioxane (8F-POSS) as a Multifunctional Modifier for Natural Rubber: Hydrogen-Bond Pattern and Network Reinforcement

Octa(3,3,3-trifluoropropyl) polyhedral oligomeric silsesquioxane (8F-POSS) was synthesized via a vertex-capping method and incorporated into natural rubber (NR) and deproteinized natural rubber (DPNR) to fabricate inorganic–organic vulcanizates. Curing characteristics, crosslink density, and the filler–rubber interaction parameter (α) were evaluated. We found that 8F-POSS retarded vulcanization kinetics but eventually enhanced network integrity. Two-dimensional infrared (2D-IR) spectroscopy indicated a hydrogen-bond shielding effect between siloxane cages and protein hydroxyl groups in NR. This interaction governed morphology development: proteins in NR acted as compatibilizers to improve initial POSS dispersion, though at high loadings they compromised reinforcement efficiency (α fell from 18.12 to 9.04). In contrast, DPNR vulcanizates showed stronger direct filler–rubber interactions, with higher α values (25.66–35.58) and a more constrained physical network. Despite a denser physical network, the 8F-POSS cages increased fractional free volume and promoted interfacial frictional slippage, leading to a synergistic “reinforcement–dissipation” effect. As a consequence, 8F-POSS/DPNR vulcanizates exhibited an enhanced damping performance (e.g., a loss factor of 1.26) alongside a depressed Tg, reduced equilibrium swelling in oil from 324% to 147%, high hydrophobicity (water contact angle above 120°), and distinctive multi-stage thermal stability. These findings demonstrate a strategy to manipulate the protein network in NR using nanoscale hybrid fillers for the design of high-performance vulcanizates.