Polyborosiloxane‐Modified Natural Rubber With Enhanced Mechanical, Thermal, and Viscoelastic Properties

ABSTRACT This study investigates polyborosiloxane (PBS) as a supramolecular viscoelastic modifier for enhancing the performance of natural rubber (NR). PBS was synthesized by reacting hydroxy‐terminated polydimethylsiloxane (PDMS–OH) with boric acid (BA), forming a dynamic network through reversible Si–O–B covalent bonds. PBS was incorporated into NR at varying loadings via two‐roll milling, followed by sulfur vulcanization. FTIR confirmed successful PBS synthesis and incorporation, while SEM revealed PBS‐loading‐dependent morphological changes. TGA demonstrated enhanced thermal stability of PBS‐modified NR relative to neat NR. Mechanical testing identified 0.5 phr as the optimal loading, yielding significant improvements in tensile strength and overall mechanical performance while inducing a controlled reduction in hardness. At higher PBS content, phase separation and agglomeration occurred, leading to diminished mechanical properties, as confirmed by SEM–EDS and boron analysis. DMA revealed a PBS‐loading‐dependent viscoelastic response, induced a reduced rubbery‐plateau storage modulus, broadened relaxation behavior, and altered damping characteristics. Overall, the results demonstrate that PBS effectively tailors the viscoelastic properties of NR at low loadings, with material performance being highly sensitive to PBS loading.