Tripropylene Glycol CAS 24800-44-0

Introduction to Tripropylene Glycol

Tripropylene Glycol is a colorless, mildly viscous liquid, a linear polyether diol formed by three propylene oxide units with a hydroxyl group at each end. The C9 backbone carries three internal ether oxygens, giving a hydroxyl value near 584 mg KOH/g and a boiling range of 265–275 °C. Formulators use it as a flexibilizing polyol in polyurethane and polyester systems, and as a slow-evaporating humectant and lubricity carrier in metalworking fluids and cosmetic bases.

The all-ether backbone stays intact at pH 3–11 and remains flexible at −40 °C, where ester polyols stiffen and saponify. One practical caution: TPG is hygroscopic, and every 0.1% of absorbed water consumes roughly 0.6% of the isocyanate budget in PU reactions, generating CO₂ bubbles in cast elastomers. Keep drums sealed and verify water by Karl Fischer (≤0.1%) before charging into NCO-containing systems.

Key Features of Tripropylene Glycol

• Triple-ether hydrolysis resistance. With no ester bond to saponify, the backbone survives pH 3–11 at 80 °C, extending service life of PU parts in humid and alkaline service.
• Low-temperature flexibility. Free-rotating ether linkages keep TPG-modified polyurethane crack-resistant at −40 °C (freezing point −45 °C, supercools on storage).
• High boiling, slow evaporation. A 265–275 °C boiling range and low vapour pressure hold coatings and inks open longer, preventing nozzle skinning and acting as a slow coalescent.
• Diol functionality at ~584 mg KOH/g. Two hydroxyls incorporate into PU and polyester networks as a flexible chain extender, lowering crosslink density in a controlled, predictable way.
• Mild, low-odor profile. Negligible odour and low volatility suit cosmetic humectant use and fragrance-sensitive formulations where shorter glycols smell too strong.

Tripropylene Glycol Chemical & Physical Properties

Applications of Tripropylene Glycol

PU elastomers and flexible foams: Charged at 5–20% of the polyol blend. Ether segments lower the soft-segment Tg and improve low-temperature flexibility, while the ~584 mg KOH/g hydroxyl value slots into standard isocyanate index calculations without re-tooling the formulation.

Metalworking and textile lubricants: Used at 2–10%. Ether oxygens adsorb onto metal and fibre surfaces, providing boundary lubricity and humectancy; full water miscibility allows semi-synthetic fluid concentrates that dilute clear.

Cosmetic humectant and solvent: Dosed at 1–5%. One extra propylene oxide unit versus DPG cuts volatility, so skin moisturisation persists longer and active ingredients (salicylic acid, botanical extracts) stay solvised without ethanol.

Inks, coatings, and cleaners: Added at 1–5% as a slow humectant and coalescent. The 265–275 °C boiling range keeps printheads and nozzle tips from skinning over during shutdowns, and extends open time of waterborne coatings.

Heat-transfer and hydraulic fluids: Blended at 20–60% with corrosion inhibitors. High boiling point, −45 °C freezing point, and stable viscosity-temperature curve hold performance from −30 °C to 150 °C in closed loops.

Storage & Safety Precautions for Tripropylene Glycol

Storage conditions. Store in sealed steel or HDPE drums at 5–35 °C, in a dry area. TPG is hygroscopic and will pull atmospheric water through any leak path, pushing KF water above 0.1% and spoiling NCO-sensitive chemistry. Keep away from strong oxidisers and isolate from isocyanate storage bays.

Safety and PPE. GHS: Not classified as hazardous. Mild eye irritant. Wear standard nitrile gloves and safety goggles during drum transfers. Spills are non-toxic but slippery; contain with inert absorbent and wash with water.

Transport classification. Non-DG. Flash point ~141–145 °C places it outside Class 3; not regulated under IMDG, IATA, or ADR. Ship as standard general cargo.

Practitioner note: For incoming QC, verify hydroxyl value by phthalic anhydride esterification per ASTM E222 (target 575–595 mg KOH/g) and water by Karl Fischer. Isomer ratio from propylene oxide addition drifts slightly between batches, so viscosity may wander ±10% around 57 mPa·s—this is cosmetic and does not shift hydroxyl value or reactivity.

Tripropylene Glycol FAQ

Q: Can Tripropylene Glycol (CAS 24800-44-0) be charged directly into NCO-containing PU systems?

A: Yes, but only after a Karl Fischer check. TPG is hygroscopic; each 0.1% of absorbed water consumes ~0.6% of the isocyanate budget and releases CO₂, leaving bubbles in cast elastomers. Require KF ≤0.1% on the COA, re-test opened drums, and use the measured hydroxyl value (575–595 mg KOH/g) in your index calculation.

Q: Why did my TPG-based coating stay tacky for hours?

A: The 265–275 °C boiling range means TPG evaporates very slowly. Above 3–5% in a film former, it acts as a permanent plasticiser and delays tack-free time. Cut the dose to 1–3%, or blend with a faster glycol ether for the first hour of drying. In inks, keep it at 1–2% and reserve higher loads for printhead humectancy.

Q: How does TPG differ from dipropylene glycol in humectancy and drying?

A: TPG carries one extra propylene oxide unit: higher boiling (265–275 °C vs ~230 °C), lower volatility, and slightly higher viscosity (~57 vs ~40 mPa·s at 25 °C). Choose TPG when you need longer open time, slower skin drying, or lower odour; choose DPG when faster evaporation and lower cost matter, as in fragrance carriers.