Synthesis of Structure-Controlled Polyborosiloxanes and Investigation on Their Viscoelastic Response to Molecular Mass of Polydimethylsiloxane Triggered by Both Chemical and Physical Interactions

Abstract

A series of polyborosiloxanes (PBSs) was synthesized by mixing hydroxy-terminated polydimethylsiloxanes (PDMS) and boric acid (BA) in toluene at 120 °C. The molecular masses of selected PDMS precursors were in a wide range, covering from below up to far above the critical entanglement molecular mass of PDMS. The reaction kinetics was followed by using Fourier transform infrared (FTIR) spectroscopy. Unreacted BA was removed from raw PBSs after the reactions. The influence of molecular mass of PDMS precursors on the rheological property of PBSs was explored by dynamic oscillatory frequency sweeps. The results showed that the plateau elastic moduli of PBSs were highly dependent on the molecular mass of PDMS precursors. The plateau elastic moduli of PBSs decreased at first and then increased with increasing molecular mass of PDMS precursors. PBS1 and PBS2 prepared from unentangled PDMS precursors showed sufficient fits by using the two-mode Maxwell model, whereas PBS3 to PBS6 prepared from highly entangled PDMS precursors showed obvious deviations from the two-mode Maxwell model. It could be concluded that the changing trend of plateau elastic modulus of PBSs versus molecular mass of PDMS precursors was determined by the number density of supramolecular interactions (Si−O:B weak bonding and hydrogen-bonding of the end groups Si−O−B(OH) 2 ) and the number density of topological entanglements.

Rheology of crosslinked entangled polymers: Shear stiffening in oscillatory shear

“…A strong absorption band located at 860 cm −1 indicates the presence of Si─CH 3 bond . Comparing PDMS with PBS5, it was found that only PBS5 had a weak absorption peak at 1339 cm −1 , indicating the presence of B─O─Si bond . Other PBSs are similar, detailed results are shown in the Supporting Information Figure S1.…”

“…The reaction kinetics were followed by Fourier transform infrared (FTIR) spectroscopy, and the rheology of PBS was studied by a rheometer. The trend of the plateau elastic modulus of PBSs relative to the molecular weight of PDMS precursors is determined by the number density of molecular interactions and the number density of topological entanglements . Liu et al .…”

Boric Acid as a Coupling Agent for Preparation of Phenolic Resin Containing Boron and Silicon with Enhanced Char Yield

“…The peak at 1270 cm −1 is the deformation vibration of SiCH 3 structure. The absorption peaks at 1078–1030 cm −1 are assigned to the SiOSi structure in BSiPR . The peak at 1015 cm −1 is the stretching vibration of CO bond in methylol structure.…”

“…The absorption peaks at 1078-1030 cm −1 are assigned to the SiOSi structure in BSiPR. [26,27] The peak at 1015 cm −1 is the stretching vibration of CO bond in methylol structure. The characteristic peaks at ≈1386 and 1422 cm −1 can be contributed to the stretching vibration of BO bond in BOC and BOB structures, respectively.…”

High-temperature structural evolution and hydrolytic stability of poly(phenylborosiloxane)

“…Polyborosiloxane (PBS) is an organosilicon hetero-oligomer in which boron atoms are introduced into the backbone of polysiloxane. PBS possesses high thermodynamic stability (Chrusciel et al, 2012), a high char yield (Tang et al, 2016;Yajima et al, 1977) and good flame retardancy (Mosurkal et al, 2011;Mosurkal et al, 2009). The ceramic conversion of borosiloxane oligomers can be initiated above 500°C in an inert atmosphere, and the obtained amorphous SiBOC can be transformed to an SiC/SiBOC nanocomposite by further pyrolysis (Devapal et al, 2010;Sreejith et al, 2016).…”