In leather tanning, textile finishing and polymer modification, physical water repellents rely on filling and adsorption, failing after a few washes; common silicone oils lack reactive sites, showing poor compatibility with polar matrices and oil bleed; traditional softeners trade hydrophilicity for hand feel; fluorinated agents carry environmental burden and yellowing risk on light shades. For demands of "terminal carboxy chemical anchoring + durable waterproof + hydrophilic softness + non-yellowing", a strictly controlled carboxy-terminated polydimethylsiloxane welds reactivity and siloxane character at both chain ends. Addressing this, Anhui IOTA Silicone Oil Co., Ltd. launches IOTA 2520 Carboxy Silicone Oil. Carboxy-terminated polydimethylsiloxane. Appearance pale yellow transparent liquid, no mechanical impurities. Viscosity 250. Acid value 45 mg/g. Active content >98.5%. Applications: durable waterproofing of chrome-tanned leather, hydrophobicity on polar surfaces, compatibility treatment for pigments/fillers, chain extender for polyester/polyamide polycondensation, hydrophilic soft finishing of fabrics. Package 190kg or 950kg drum. Store sealed original container at -20℃~50℃, shelf life 24 months. Brand IOTA. System Positioning: Carboxy-Terminated PDMS Among Reactive Silicone Oils Within functional silicone oils, IOTA 2520 is a carboxy-terminated PDMS, distinct from hydroxy-terminated silicone (slow condensation, weak anchor), amino silicone (yellowing, uncontrolled reaction), epoxy silicone (strong cationic activity, light-shade risk), ordinary dimethylsilicone (no reactive site, physical spread only). IOTA 2520 uses terminal carboxyls as chemical handles—coordinating with collagen amino groups and chromium complexes in tanning, and participating in polyester/polyamide chain extension—positioning as "durable waterproofing agent for chrome-tanned leather + hydrophobic modifier for polar surfaces + interfacial compatibilizer for pigments/fillers + silicone chain extender for PET/PA + hydrophilic softener for fabrics", rather than mere lubricant or defoamer. Molecular Architecture: Dual Carboxy Ends + PDMS Backbone + Viscosity 250 + Acid Value 45 IOTA 2520 core is a polydimethylsiloxane backbone capped with carboxyl groups at both ends. Terminal carboxyls are strongly polar and reactive: during chrome tanning they form ionic or coordination bonds with collagen fibers and Cr³⁺ complexes, locking siloxane chains into the fiber network. The PDMS segment delivers low surface energy, flexibility, thermal stability and weatherability, making the waterproof layer soft, not brittle. Viscosity 250 fits dipping, roll-coating and emulsion formulation; acid value 45 mg/g corresponds to stable carboxy equivalents; active content >98.5% means low free acid and oligomers, minimizing yellowing in light-colored systems. Performance Leap: From "Physical Adsorption, Wash-Off" to "Carboxy-Terminated, Chemical Anchor" With IOTA 2520, four-way synergy: durable waterproof—carboxy bonding replaces physical adsorption, resisting bend, knead and repeated washing without migration; hydrophilic softness—siloxane chains orient outward for dry silky feel while carboxyls retain inward hydrophilic sites, breaking the "soft equals hydrophobic" rule for sportswear and underwear; interfacial compatibilization—treating pigments/fillers lowers inorganic/organic interfacial tension, improving dispersion and composite stability; polymer functionalization—as chain extender in PET/PA polycondensation, embedding silicone segments for anti-block, anti-stick, abrasion and scratch resistance. Application Penetration: From Chrome-Tanned Leather to Engineering Polymers IOTA 2520 covers five core scenarios.

• Chrome-tanned leather: shoe upper, furniture, automotive interior—durable waterproof; add mid/late tanning stage, bonds to fiber, non-yellowing on light leather.
• Polar surface hydrophobicity: glass fiber, metal oxide, polar films—low-surface-energy modification with balanced coating adhesion.
• Pigment/filler treatment: TiO₂, calcium carbonate, fumed silica—compatibility; improve dispersion in organic polymers.
• Polyester/polyamide chain extension: modified TPEE/TPAE, films, engineering plastics—silicone functionality embedded in backbone.
• Fabric hydrophilic softening: cotton, polyester, nylon finishing—dry silky hand; pad-dry or exhaust process lifts hand feel and moisture management.

⚠️ Taboo: terminal carboxyl is reactive, avoid long high-temp open-container exposure to prevent viscosity rise; control pH and shear in micro-emulsion to avoid breaking; avoid prolonged contact with strong base/amines; validate yellowing and compatibility on light shades before scale-up. IOTA Technical Guide: 190kg/950kg Drum, Original Sealed 24 Months IOTA 2520 is pale yellow transparent liquid. Leather waterproof: 0.5%~2.0% of leather weight added mid/late tanning; textile finishing: 1%~3% of fabric weight with auxiliary blend; polymer chain extension: 0.1%~2.0% by target MW and silicone content; filler treatment: 0.5%~3.0% of filler weight. Store sealed original container at -20℃~50℃, away from heat and moisture; shelf life 24 months. Industry Insight: Carboxy silicone selection is not the lower viscosity the better, but using terminal carboxy equivalent for reaction degree, backbone length for flexibility and waterproofing, active content for light-color stability, micro-emulsion acid/alkali/shear resistance for process window. For leather chemists, textile finishers and polymer synthesis engineers, IOTA 2520 uses one carboxy-terminated PDMS across durable waterproofing, hydrophilic softening and silicone functionalization, taking carboxy-terminated polysiloxane and leather-fiber hydro-soft as batch-checkable anchors, securing functionality and appearance simultaneously.