Effect of Molecular Weight of the Precursor Polydimethylsiloxane on the Rheology of Polyborodimethylsiloxane (PBDMS)

Abstract This study presents effect of the molecular mass of hydroxyl‐terminated polydimethylsiloxane (OH‐PDMS) precursors on the rheological behavior, molecular weight, and polydispersity (PD) of shear‐stiffening gel (STG) of polyborodimethylsiloxane (PBDMS). The STG of PBDMS was synthesized by condensation of boric acid with different molecular weights of hydroxy‐terminated polydimethylsiloxanes (PDMS‐OH) in toluene at 120 °C. Fourier transform infrared (FTIR) spectroscopy and gel permeation chromatography (GPC) analyses provided detailed insights into the molecular weight and kinetics of Si─O─B bonding, revealing novel correlations between precursor molecular weight, polydispersity, and rheological behavior. The findings demonstrated that lower molecular weight PDMS precursors enhance the shear‐thickening effect by increasing the density of covalent Si─O─B bonds, resulting in greater energy absorption and terminal relaxation. Rheological studies confirmed that shorter PDMS chain lengths facilitate higher storage modulus values and dynamic stiffness under strain, outperforming previous results in terms of material toughness and robustness. This work provides a new methodology for optimizing the mechanical properties of PBDMS elastomers, paving the way for advanced applications in impact‐resistant, self‐healing, and energy‐dissipating materials.