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In the silicone materials family, hydroxyl silicone oil (hydroxyl-terminated polydimethylsiloxane) has long played a pivotal role thanks to its reactive terminal hydroxyl groups. It serves as the base polymer for room-temperature-vulcanizing (RTV) silicone rubber (107 gum), the structure control agent for addition-cure liquid silicone rubber (LSR), and the starting material for countless modified silicones. Since 2026, breakthroughs in precision molecular design have transformed hydroxyl silicone oil from a "generic base material" into a "customizable functional material," opening new frontiers in electronic packaging, biomedicine, and green textiles.
Hydroxyl silicone oil is a linear polysiloxane with reactive hydroxyl groups at both chain ends. This molecular feature — the terminal Si-OH — is the source of its remarkable versatility:
Crosslinking Capability: Under catalyst action, terminal hydroxyl groups undergo condensation reactions with crosslinkers (silicates, ketoxime silanes, etc.), forming three-dimensional networks — the fundamental chemistry behind one- and two-component RTV silicone rubber.
Structure Control Function: In high-temperature-vulcanizing (HTV) silicone rubber, hydroxyl silicone oil acts as a structure control agent, interacting with silanol groups on silica filler surfaces to prevent "structuring" (viscosity increase and processability degradation during storage) while improving product transparency.
Compatibility and Reactivity: The terminal hydroxyl groups impart higher polarity, enabling interaction or chemical bonding with various organic materials and inorganic fillers.
Viscosity classification: products with viscosity ≤2,500 mPa·s are termed hydroxyl silicone oil; those with higher viscosity are referred to as 107 silicone rubber.
| Viscosity Range | Product Category | Core Applications |
|---|---|---|
| 10-50 mPa·s | Low-viscosity hydroxyl oil | Fabric finishes, structure control agents, defoamer raw materials |
| 100-500 mPa·s | Medium-viscosity hydroxyl oil | Electronic potting compounds, water repellents, release agents |
| 800-2,500 mPa·s | High-viscosity hydroxyl oil | RTV sealant base polymers, mold-making base gums |
| >2,500 mPa·s | 107 silicone rubber | Construction sealants, electronic potting, thermal interface materials |
In March 2026, a patent for "Preparation method of polysiloxane with hydrogen at one end and methyl at the other end" was published, solving long-standing challenges in single-hydrogen-terminated polysiloxane production.
The technology uses siloxane cyclics, trimethylchlorosilane, and reactive-hydrogen-containing chlorosilanes as raw materials, proceeding through cationic ring-opening polymerization, hydrolysis, and metathesis under mild conditions.
Key advantages:
Mild, easily controlled reaction conditions
Fewer side reactions and byproducts, simplifying purification
No further separation or purification required — the product is directly usable
Under platinum catalysis, this product undergoes hydrosilylation with unsaturated bonds to produce various mono-reactive-group-terminated polysiloxanes — providing critical building blocks for silicone block copolymers, surface modifiers, and functional additives.
Also in March 2026, a patent for "Reactive silicone oil and its preparation method and application" was granted. Starting from hydroxyl silicone oil, the technology introduces hydrogen-containing silicone oil segments and vinyl silicone oil segments through a two-step reaction.
Application value: When this reactive silicone oil replaces conventional dimethyl silicone oil in potting compounds, it reduces compound viscosity while significantly minimizing the "bleeding" phenomenon commonly associated with dimethyl silicone oil — a long-standing challenge in electronic potting.
In May 2026, a patent for "High-efficiency catalyst for hydrosilylation reaction and its preparation method" introduced an innovative microencapsulated catalyst approach.
The core innovation involves modifying methyl-terminated hydroxyl silicone oil with silazane, then forming a microcapsule coating system with paraffin — controlling catalyst release to achieve lower initial reactivity. This improves reaction uniformity within silicone rubber, enhancing transparency and overall strength.
This technology is particularly significant for addition-cure LSR, LED encapsulants, and optical-grade silicone rubbers with demanding transparency and mechanical property requirements.
Hydroxyl silicone oil as a structure control agent for HTV silicone rubber is one of its most traditional and high-volume applications.
Traditional challenges: After silica reinforcement, HTV compounds undergo "structuring" during storage — viscosity increases and processability degrades. While adding hydroxyl silicone oil or diphenylsilanediol mitigates this issue, traditional products suffer from:
Fluctuating hydroxyl content leading to inconsistent control
High low-molecular-weight content affecting transparency and high-temperature performance
Impurity ions making them unsuitable for electronic/medical grades
Next-generation product features: "Electronic-grade hydroxyl silicone oil" introduced in 2026 achieves:
High purity: Clear, low cyclic content (D3-D10 <300 ppm)
No impurity ions: No trimethylamine, no sodium ions, no chloride ions
Precise control: Hydroxyl content and viscosity ratios accurately specified
Improved processability: Better dispersion and more stable structure control
In 2026, hydroxyl silicone oil applications in textile softeners and premium personal care products have achieved new breakthroughs.
Textile innovation: A patent published in February 2026 uses hydroxyl-terminated polymethylsiloxane with hydroxypropyl-β-cyclodextrin (a bio-based modifier) to produce emulsions with softening, lubrication, and film-forming functions.
The innovation leverages hydroxyl silicone oil's reactivity to form chemical bonds with active groups on fiber surfaces — delivering "wash-resistant" softness. Compared to conventional polyether-modified silicones, hydroxyl silicone oil provides a fuller, richer silky feel, making it particularly attractive for high-end underwear and activewear finishing.
Personal care trend: As a volatile silicone alternative, hydroxyl silicone oil's safety profile is gaining attention. Its polarity and biocompatibility make it suitable for long-lasting moisturizers and hair care oils. The "clean beauty" trend has positioned hydroxyl silicone oil derivatives offering long-lasting conditioning without bioaccumulation risk as popular candidates for formulation upgrades.
As synthesis technologies advance and application areas expand, hydroxyl silicone oil is transitioning from "base material" to "functional material." Future development directions include:
Higher purity: ppb-level metal ion content for electronic/medical grades
Precision molecular design: Accurate control over molecular weight and functional group positioning
Bio-based pathways: Green synthesis using renewable raw materials
Functional composites: Development of thermally/electrically conductive, flame-retardant modified grades
From construction sealant base polymers to 5G base station potting compounds, from textile softeners to "clean" personal care ingredients, hydroxyl silicone oil's molecular engineering is opening a new chapter in functional materials.
