1. Reaction Mechanism & Products
   Core Reaction: The terminal hydroxyl groups (-OH) of dihydroxy silicone oil condense with the hydroxyl groups of boric acid (H₃BO₃) to form B-O-Si bonds and water molecules.
   Main Products:

• Polyborosiloxane (PBS): Boric acid acts as a crosslinker to connect multiple silicone molecular chains and form a crosslinked network structure.
• Boron-terminated silicone oil: Boron atoms cap silicone chains when boric acid is used in excess.
  Simplified reaction formula:
  n HO-Si(CH₃)₂O-[Si(CH₃)₂O]ₘ-Si(CH₃)₂-OH + n H₃BO₃ → [-O-Si(CH₃)₂O-[Si(CH₃)₂O]ₘ-Si(CH₃)₂-O-]ₙB + 2n H₂O

2. Typical Reaction Conditions

   Temperature: 100–180°C; higher temperatures accelerate reaction and complete dehydration

   Reaction Time: 1–5 hours; adjust based on temperature and system to guarantee sufficient reaction

   Pressure: Atmospheric or reduced pressure (13–14 kPa); vacuum facilitates water removal and drives reaction forward

   Catalyst (Optional): FeCl₃ etc.; accelerates crosslinking especially at low temperatures

   Solvent: Toluene or solvent-free system; solvents improve mixing uniformity while solvent-free processes suit high-viscosity products

   Material Ratio: Silicone oil : boric acid = 10–100 : 1 by mass; ratio governs crosslink density and final material properties
3. Application Scenarios

   (1) Shear-thickening materials: Polyborosiloxane exhibits shear thickening behavior for fragment-proof fabrics and ballistic protection materials

   (2) Self-healing materials: Reversible dynamic B-O-Si bonds endow materials with self-repair performance for anti-icing coatings

   (3) High-temperature resistant materials: Boron-terminated silicone oil produces high-temperature resistant silicone rubber with low thermal loss

   (4) Flame retardant materials: Polyborosiloxane compounded with platinum additives improves flame resistance of silicone sealants

   (5) Play dough: Crosslink with boric acid to form oily gel as base material for modeling clay
4. Key Influencing Factors

   Molecular weight: Low-molecular-weight dihydroxy silicone oil (500–2000) reacts more readily; molecular weight determines viscosity and mechanical properties of finished products

   Water content: Generated water must be continuously removed to avoid reaction inhibition

   Atmosphere: Nitrogen shielding prevents oxidation during high-temperature processing

Summary

The condensation reaction between dihydroxy silicone oil and boric acid is well-defined and adjustable. Products ranging from boron-terminated silicone oil to crosslinked polyborosiloxane can be prepared by controlling temperature, material ratio, pressure and other parameters, with wide applications in specialty materials.