Microwave‐Assisted Polyborodimethylsiloxane Synthesis: Influence of <scp>PDMS</scp> Viscosities on Viscoelastic Behavior

ABSTRACT Polyborodimethylsiloxane (PBDMS) was synthesized via a solvent‐free, microwave‐assisted method through the reaction of hydroxy‐terminated polydimethylsiloxane (PDMS) with boric acid. This approach achieved remarkable time efficiency, reducing the reaction duration from nearly 24 h to merely 10 min. The resulting dynamic covalent polymer exhibits tunable viscoelastic behavior arising from reversible boron‐based interactions within its network. To investigate the influence of precursor characteristics PDMS precursors of varying viscosities were employed. FTIR spectra confirmed the formation of SiOB linkages, with bond intensity decreasing as precursor viscosity increased. For the lowest‐viscosity precursor (500 cSt), rapid SiOB formation within 10 min indicated complete condensation, while the disappearance of BOB and BOH bands confirmed efficient consumption of boric acid. Gel permeation chromatography analysis revealed molecular weight reduction and increased polydispersity for low‐viscosity precursors, suggesting chain scission and greater molecular heterogeneity. In contrast, polymers synthesized from higher‐viscosity precursors (35,000 and 50,000 cSt) exhibited only minor molecular weight reduction, indicating limited degradation and potential branching. Over time, molecular weight decreased gradually with stable polydispersity, reflecting controlled chain scission and minimal crosslinking. Dynamic rheological analysis showed significant enhancement in the storage and loss moduli of PBDMS compared to unmodified PDMS. The plateau modulus was strongly influenced by precursor viscosity due to supramolecular boronate “sticker” interactions contributing to transient crosslinking and topological entanglement. Overall, this microwave‐assisted, solvent‐free route offers a rapid and scalable approach to synthesize PBDMS with tunable viscoelastic properties for high‐performance elastomeric applications.