Effect of Boric Acid on the Structure and Properties of Borosiloxanes

Borosiloxane materials obtained by mixing and thermostatting of hydroxyl-terminated polydimethylsiloxane and boric acid are studied. Samples synthesized at room temperature and at a temperature above 220°С are nontransparent rubberlike masses. Washing of boric acid yields single-phase transparent borosiloxanes demonstrating the rubberlike behavior. Studies are carried out using elemental analysis, dynamic light scattering, synchronous thermal analysis, and polarization optical microscopy. The viscoelastic properties of the samples are characterized by rheological methods and the ability of polymer ball-like samples to spread and rebound. It is shown that in initial states they contain boric acid microcrystalline inclusions that scatter visible light. An increase in the synthesis temperature and the presence of unreacted boric acid improve the elasticity of the materials and decrease their thermal stability. The content of boron in borosiloxane obtained at an increased temperature is an order of magnitude higher than that in borosiloxane synthesized at room temperature, whereas the radius of the effective hydrodynamic sphere is smaller by a factor of 5 than that in the high-temperature borosiloxane. The rheological properties of the tested samples are different. These materials show promise as components of multilayer self-healing and shock-absorbing composites and materials with controlled tackiness.