ℹ TMA's Bifunctional Reactivity - Why One Molecule Does Two Jobs TMA's unique molecular architecture - anhydride ring at C1/C2, free –COOH at C4 - enables two distinct reaction modes in a single molecule: (1) Anhydride ring-opening esterification with alcohols (fast, exothermic, typically no catalyst required at 130–180°C) produces the half-ester (monoester with free –COOH at C4); continued reaction with excess alcohol or elevated temperature closes the second ester bond to yield the trimellitate diester or triester. (2) Free carboxyl group at C4 can independently react with epoxies (ring-opening), amines (amide formation), metal oxides (metal salt), or hydroxyl groups (polycondensation) - enabling TMA to function simultaneously as an esterification acid and a cross-linking acid in polyester and alkyd resin synthesis. This bifunctionality is the structural basis for TMA's versatility across plasticisers, polyester resins, polyimides, and epoxy curing agent applications.

Parameter	Specification	Typical / Actual	Test Method / Note
Appearance	White crystalline powder	White, free-flowing	Visual inspection; slight characteristic odour; hygroscopic - keep sealed
Purity	≥99.5 wt%	99.8 wt%	HPLC; high purity minimises trimellitic acid, phthalic anhydride, and other isomeric impurities
Acid Value	630–645 mg KOH/g	638 mg KOH/g	GB/T 7304-2014; reflects combined anhydride + free –COOH acidity; use COA AV for ester charge calculation
Melting Point	164–168°C	166°C	GB/T 617-2006; sharp melting range (≤4°C spread) confirms high crystalline purity; broad range indicates hydrolysis or impurity
Moisture	≤0.1 wt%	0.05 wt%	Karl Fischer; TMA + H₂O → trimellitic acid (hydrolysis); excess moisture impedes anhydride ring-opening kinetics in esterification
Ash Content	≤0.05 wt%	0.02 wt%	GB/T 6378.2-2001; low ash confirms catalyst (Co/Mn/Br) removal completeness; critical for cable-grade TM810 volume resistivity compliance
Color (Pt-Co, 50% in acetone)	≤20 Pt-Co	10 Pt-Co	GB/T 3143-1982; measured in 50% acetone solution; pale colour propagates to downstream ester and resin products
Packaging	25 kg paper-plastic composite bag / 1000 kg FIBC ton bag	Inner PE film liner	Bags sealed with PE inner liner; moisture-proof outer; max 8-layer stacking for 25 kg bags; FIBC single-layer only; shelf life 12 months

COA per shipment: Purity (HPLC) · Acid value (GB/T 7304-2014) · Melting point (GB/T 617-2006) · Moisture (Karl Fischer) · Ash content (GB/T 6378.2-2001) · Color Pt-Co (GB/T 3143-1982). Third-party pre-shipment inspection by SGS, Intertek, or Bureau Veritas available on request.

Why TMA purity matters for ester synthesis: The primary impurities in lower-grade TMA are trimellitic acid (hydrolysed anhydride, increases moisture demand in esterification), phthalic anhydride isomers (alter the three-ester architecture of the trimellitate product), and inorganic ash (catalyst residues that reduce volume resistivity in cable-grade ester plasticisers). Sinolook's ≥99.5% purity TMA (actual 99.8%) ensures predictable stoichiometry, low by-product formation, and consistently low colour and ash in downstream TM810 and TOTM ester products.

TMA is the essential upstream feedstock for all commercial trimellitate ester plasticisers and lubricants. Each mole of trimellitate triester requires one mole of TMA esterified with three moles of alcohol. The esterification reaction proceeds via anhydride ring-opening (fast, low-temperature first step producing half-ester) followed by esterification of the free C4 carboxyl and the remaining acid hydroxyl at elevated temperature (typically 180–220°C with acid or titanium alkoxide catalyst) to yield the fully esterified triester product.

TM810 synthesis: TMA + mixed n-octanol / n-decanol (C8/C10) → Tri(octyl,decyl) trimellitate (TM810, CAS 68515-42-4). TMA's purity directly determines TM810's acid value, colour, and electrical properties - high-ash TMA produces TM810 with low volume resistivity, failing IEC 60811 cable insulation specifications. TOTM synthesis: TMA + 2-ethylhexanol → Tris(2-ethylhexyl) trimellitate (TOTM, CAS 3319-31-1). Both TM810 and TOTM are supplied by Sinolook, and TMA is available from the same supply chain as a single-source procurement option.

The trimellitate ester products (TM810, TOTM) are used as high-performance non-phthalate plasticisers for 105°C-rated PVC cable insulation, automotive interior PVC, and medical device PVC - all applications where TMA's three ester groups per molecule deliver the low volatility and high-temperature stability that two-ester phthalate plasticisers cannot match. For detailed downstream application data, see the TM810 and TOTM product pages.

In saturated polyester and alkyd resin synthesis, TMA functions as a trifunctional branching monomer: its two adjacent carboxyl groups (anhydride ring) react with diol or polyol monomers in the polycondensation, while the free C4 carboxyl group either introduces additional branching points or remains as a pendant acid group for water-dispersibility (in waterborne resins) or cross-linking sites (in baking resins). This trifunctionality at controlled loading (typically 2–10 mol% TMA replacement of phthalic or isophthalic acid) allows formulators to tune resin molecular weight, branching density, hydroxyl and acid values, and hardness.

TMA-modified polyester resins exhibit superior adhesion, chemical resistance, and weather resistance compared to linear (bifunctional acid only) equivalents, making them suitable for high-gloss industrial coatings, marine anti-corrosion coatings, and high-temperature baking coatings for automotive OEM applications. TMA also introduces acid groups that improve metallic substrate adhesion without requiring additional adhesion promoter additives.

TMA's free carboxyl group at C4 is the key functional group for producing water-dispersible and water-soluble polyester and acrylic resins for waterborne coating systems. By controlling TMA content in the resin backbone, formulators introduce the specific acid value required for amine neutralisation and water dispersibility - typically targeting resin acid values of 30–60 mg KOH/g for waterborne polyester dispersions. The resulting waterborne coatings reduce VOC content to ≤150 g/L (compliant with EU Directive 2004/42/EC and EPA OTC Model Rule), while maintaining the gloss, hardness, and chemical resistance of solventborne equivalents.

TMA also functions directly as an epoxy resin curing agent (hardener): the anhydride ring opens with the epoxy group in a ring-opening addition reaction at 120–180°C, forming an ester linkage and a hydroxyl group that subsequently reacts further. TMA-cured epoxy systems exhibit high heat distortion temperature (HDT >150°C), excellent chemical resistance, and low shrinkage - used in electrical potting compounds, high-temperature adhesives, and composite laminates.

Polyimide synthesis: TMA reacts with aromatic diamines in a two-step poly(amic acid) → imidisation route to produce TMA-based polyimide and polyamide-imide (PAI) resins. PAI (produced from TMA + 4,4'-methylenedianiline or MDI) exhibits exceptional thermal stability (continuous service to 220–260°C), high strength, and excellent electrical insulation - used in aerospace structural components, motor magnet wire insulation (Class H/220), printed circuit board substrates, and flexible electronics. The commercial PAI resin Torlon (Solvay) is TMA-based, establishing TMA as the core anhydride monomer for this high-performance polymer class.

Rubber crosslinking: TMA (as trimellitic acid trianhydride) and its partial metal salts are used as vulcanisation co-agents and crosslinking systems in fluoroelastomers (FKM) and acrylic rubbers (ACM), improving tensile strength, heat resistance, and chemical resistance of cured rubber compounds used in automotive seals, gaskets, and O-rings.

Other specialty uses: TMA-derived imide intermediates are used in pharmaceutical synthesis as biocompatible intermediates. TMA is also used as a reactive modifier in polyurethane resin synthesis to introduce carboxyl functionality and improve adhesion to polar substrates. Growing demand from new energy vehicle (NEV) motor insulation, 5G flexible circuit substrates, and aerospace TMA-based PAI composites is driving increasing global TMA consumption growth.

Single-source benefit: COA acid value and colour data on TMA are directly comparable with the corresponding specifications on TM810 and TOTM finished product COAs - enabling traceability from raw material to finished plasticiser across a single consistent quality system. Contact Sinolook to discuss TMA + TM810/TOTM combined procurement packages.

⚠ TMA is hygroscopic - it hydrolyses to trimellitic acid on prolonged moisture exposure. The anhydride ring absorbs atmospheric moisture (TMA + H₂O → trimellitic acid), raising acid value and reducing esterification reactivity. Keep containers sealed at all times. Store in low-humidity conditions (RH <60%). GHS hazards: Skin Irrit. 2 (H315), Eye Irrit. 2 (H319), STOT SE 3 (H335 - dust inhalation irritation). Wear dust mask, chemical-resistant gloves, and safety goggles when handling. TMA powder/dust can cause skin and eye irritation on contact with moisture.

Q: What is the stoichiometric TMA:alcohol ratio for TM810 and TOTM ester synthesis?

The theoretical ratio is 1 mol TMA : 3 mol alcohol for the fully esterified trimellitate triester (all three carboxyl groups esterified). Using the molecular weights: for TM810, TMA (MW 192.13) + mixed C8/C10 alcohol blend (~MW 136 average); for TOTM, TMA + 2-ethylhexanol (MW 130.23). The practical alcohol charge typically uses a 5–15% molar excess of alcohol to drive complete esterification (Le Chatelier), with excess alcohol removed by vacuum distillation at the end of reaction. Always use the COA acid value of the TMA batch for batch-specific charge calculations rather than the nominal theoretical value, as the actual acid value directly reflects the anhydride + free –COOH content of that specific batch.

Q: Why is low ash content in TMA critical for cable-grade TM810 plasticiser?

Ash content in TMA reflects inorganic residues - primarily cobalt, manganese, and bromine catalyst remnants from the pseudocumene oxidation step. These ionic impurities carry through into the esterified TM810 product: metal ions and halide ions in the final TM810 plasticiser act as ionic charge carriers, dramatically reducing the volume resistivity of the PVC compound below the IEC 60811 requirement of ≥5×10¹¹ Ω·cm for 105°C cable insulation. Sinolook's TMA ash content of ≤0.05% (actual 0.02%) ensures that catalyst-derived ionic contaminants do not compromise the electrical insulation performance of downstream TM810 in cable compound applications. When comparing TMA suppliers, always request the ash content test result - low-purity TMA with high ash is the primary cause of TM810 volume resistivity failures in cable compound qualification testing.

Q: What is the difference between trimellitic anhydride (TMA) and pyromellitic dianhydride (PMDA) - which do I need?

TMA (CAS 552-30-7) and PMDA (pyromellitic dianhydride, CAS 89-32-7) are both aromatic acid anhydrides but with different structures and applications. TMA (benzene-1,2,4-tricarboxylic anhydride) has one anhydride ring + one free –COOH, making it trifunctional and the feedstock for trimellitate esters (TM810, TOTM) and polyamide-imide resins. PMDA (benzene-1,2,4,5-tetracarboxylic dianhydride) has two anhydride rings and is the feedstock for pyromellitate esters (TOPM) and polyimide (PI) films (Kapton-type). If you are synthesising TM810 or TOTM trimellitate esters or TMA-based polyester/alkyd resins, you need TMA. If you are synthesising TOPM tetraester lubricant/plasticiser or PI films, you need PMDA. Sinolook supplies both - contact us to confirm which intermediate matches your downstream synthesis.

Q: Can TMA be substituted with trimellitic acid (TM acid) - are they interchangeable in esterification?

TMA (the anhydride) and trimellitic acid (the corresponding triacid, CAS 528-44-9) are functionally related but not directly interchangeable in esterification. TMA's anhydride ring opens rapidly with alcohols at 100–150°C without strong acid catalyst (anhydride is significantly more reactive than a free –COOH), enabling faster initial esterification and lower-temperature process start. Trimellitic acid produces water at each esterification step, typically requiring higher temperatures (>180°C) or azeotropic water removal. For large-scale industrial TM810 and TOTM production, TMA is the standard feedstock. Trimellitic acid is occasionally used in waterborne resin synthesis where the free acid dissolution in alkaline water is desired. If your process currently uses trimellitic acid and you wish to switch to TMA, note that TMA has a higher effective acidity per gram (AV 630–645 vs triacid AV ~440 mg KOH/g) - charge calculations must be adjusted accordingly. Contact Sinolook's technical team for process conversion guidance.

Related products: TM810 (Tri(octyl,decyl) Trimellitate, CAS 68515-42-4) - finished trimellitate ester plasticiser  ·  TOPM (Tetraoctyl Pyromellitate, CAS 3126-80-5) - four-ester pyromellitate ester  ·  INA (Isononanoic Acid)  ·  NMP (N-Methyl-2-pyrrolidinone)  ·  Maleic Anhydride (MAH)