Pyromellitic Dianhydride (PMDA) — CAS 89-32-7, 99.95% Electronic Grade For Polyimide, Metal Ions ≤1 Ppm

Pyromellitic Dianhydride (PMDA) - CAS 89-32-7

99.95% assay · Moisture 238 ppm · Free acid 0.10% · TMA 0.02% · Cu/Ca/Na/K non-detect · D50 255 µm free-flowing powder

⚠️ Read this before you evaluate the specification: PMDA is a respiratory sensitiser.

Under EU CLP, pyromellitic dianhydride carries signal word Danger with H334 (may cause allergy or asthma symptoms or breathing difficulties if inhaled), H317 (may cause an allergic skin reaction) and H318 (causes serious eye damage). Acid anhydrides as a class are associated with occupational asthma, and PMDA specifically has been linked to it.

Sensitisation is not dose-dependent once established - a worker who becomes sensitised can react to exposures far below any previously tolerated level. This is a containment and engineering-control problem, not a respirator problem. If your plant is not set up for closed-transfer handling of a sensitising powder, resolve that before ordering. We would rather lose the order than have you discover this after the drums arrive. Handling detail is in the storage section below.

💧 Moisture - every water molecule destroys one anhydride ring

PMDA is hygroscopic and hydrolyses to pyromellitic acid (CAS 89-05-4) on contact with atmospheric moisture. Hydrolysed material no longer participates in the amic-acid condensation, so it does two damaging things at once: it removes dianhydride from the stoichiometric balance, and it introduces free carboxyl that skews the ratio further.

To put the spec in perspective - 1 kg of PMDA contains roughly 9.17 mol of anhydride rings. At the 500 ppm limit, the 27.8 mmol of water present can consume about 0.30% of those rings. At our actual 238 ppm, that falls to roughly 0.14%. Because poly(amic acid) chain length follows Carothers' relationship, a fraction of a percent off stoichiometry translates into a disproportionate loss of attainable degree of polymerisation - which shows up in the finished film as low intrinsic viscosity, brittleness and poor tensile strength.

Calculation shown for orientation only; it assumes complete hydrolysis of one ring per mole of water and ignores moisture picked up after the drum is opened. Your own handling discipline matters at least as much as the incoming spec.

🧫 Free acid - the direct measure of how much of the lot is already dead

Free acid is pyromellitic acid that has already formed, whether during production, storage or transport. It is the most honest single indicator of dianhydride effectiveness, because unlike moisture it captures hydrolysis that has already happened rather than hydrolysis waiting to happen. A specification of ≤0.5% is normal for industrial PMDA; ≤0.15% is where film-grade material sits. This lot tests 0.10%.

✂️ TMA content - an under-oxidation by-product that terminates chains

Trimellitic anhydride is the characteristic by-product of incomplete durene oxidation: one methyl group short of full conversion. It carries a single anhydride ring plus a free carboxyl, which makes it monofunctional in amic-acid polymerisation. It reacts with a diamine and then stops - it caps the chain instead of extending it.

At the 0.2% specification limit, TMA amounts to roughly 0.23 mol% relative to PMDA. At the actual 0.02%, about 0.02 mol%. For thick coatings and moulding compounds this difference is invisible; for a 12.5–25 µm flexible-circuit film where mechanical margin is thin, it is not. If you are qualifying PMDA for film, TMA content is the parameter most worth arguing about with a supplier.

⚡ Metal ions ≤1 ppm - why polyimide film makers ask for them

Polyimide's commercial value is as a dielectric. Mobile alkali ions - sodium and potassium in particular - depress volume resistivity and migrate under sustained field, which is precisely the failure mode a flexible printed circuit or chip-on-film substrate cannot tolerate. Iron and copper play a different role: they catalyse thermal-oxidative degradation during the 300–400 °C imidisation bake, which shows up as colour drift and reduced long-term thermal endurance. Cu, Ca, Na and K all non-detect with Fe at 0.04 ppm is what puts this material in electronic-grade territory rather than industrial.

🧹 Insolubles, particle size and flow - the unglamorous parameters

DMF-insolubles 13.6 ppm: undissolved particulate survives filtration into the casting solution and becomes a pinhole or an inclusion in a thin film. It is a defect-density parameter, not a purity parameter.

D50 255 µm, 98.9% within 80–500 µm, angle of repose 35.3°: a genuinely free-flowing coarse powder. This matters twice over - it feeds reliably through automated dosing without bridging, and because it is not a fine dust it generates substantially less airborne material during transfer. For a respiratory sensitiser, particle size is a safety parameter as much as a handling one.

01Crude oil - own import quota, own tank farm, pipelines and transport fleet

02Integrated refining - in-house C10 aromatics production

03Durene separation - rectification, enrichment, crystallisation and separation; 40,000 t/a design capacity, ≥96% durene, naphthalene non-detect

04Gas-phase catalytic oxidation - durene oxidised to PMDA

05Purification and classification - sublimation/recrystallisation, controlled particle sizing, nitrogen-sealed packing

✅ What this buys you: feedstock traceable to the crude cargo, and a durene isomer profile that does not shift when merchant supply tightens. Since incomplete durene oxidation is exactly what generates the TMA chain-terminator, control of the feedstock is upstream control of the parameter film makers care about most. The plant is also the first facility to run this chain end-to-end under one owner, and has been qualified by several global tier-one users.

⚠️ Capacity - stated plainly. The PMDA plant is designed for 20,000 t/a, but only a 3,000 t/a line is commissioned today; Phase II is under construction. Treat 20,000 t/a as a build-out target, not as available tonnage. If you are planning a multi-thousand-tonne annual contract, tell us the volume early so we can confirm allocation against the commissioned line rather than the nameplate. We will not quote against capacity that is not running.

🎞️ 1. Polyimide Film & Varnish - the dominant outlet

PMDA condensed with 4,4′-oxydianiline (ODA) in NMP or DMAc gives poly(amic acid), which is cast and thermally imidised into the classic PMDA-ODA polyimide film. End uses: flexible printed circuit substrates, chip-on-film, flexible display backplanes, high-temperature adhesive tape, motor and transformer slot insulation, and lithium-battery separator coatings. The same chemistry in solution form gives polyimide wire enamel for magnet wire and polyimide varnishes for electrical impregnation.

🔗 Solvent for this chemistry: NMP (N-Methyl-2-pyrrolidinone), electronic and battery grade

🧊 2. Pyromellitate Ester Plasticisers & Synthetic Ester Base Oils

Esterified with 2-ethylhexanol, PMDA gives tetraoctyl pyromellitate (TOPM) - a four-ester aromatic plasticiser for 125 °C-plus wire and cable, and a base ester for high-temperature chain oils and air-compressor oils where the four ester groups give far lower thermal volatility than trimellitate or phthalate esters.

🔗 Finished ester we already supply: Tetraoctyl Pyromellitate (TOPM)

🔥 3. High-Tg Epoxy Curing Agent

As a tetrafunctional anhydride hardener PMDA delivers crosslink density and glass transition temperature that no monoanhydride can reach, for electrical castings, encapsulation compounds, moulding powders and high-temperature adhesives. The trade-off is real: high reactivity, a short pot life, and a brittle cured network unless it is blended with a flexibilising co-anhydride. It is rarely used neat.

🔗 Compare the trifunctional route: Trimellitic Anhydride as an Epoxy Curing Agent

♻️ 4. PET Chain Extender & Branching Agent

Added at low loading during PET reprocessing, PMDA reacts with terminal hydroxyl and carboxyl groups to rebuild intrinsic viscosity and introduce long-chain branching. This raises melt strength enough for extrusion foaming and thermoforming, and is one of the more practical routes to upcycling post-consumer PET rather than downcycling it.

🧫 5. Membranes, Resins & Specialty Intermediates

Polyimide gas-separation and pervaporation membranes; crosslinker and hardening component in polyester and alkyd coating resins; intermediate for polyimide aerogels, foams and fibres; and a building block for metal-organic frameworks and specialty imide chemistry.

🫁 Respiratory sensitiser controls - engineering first, PPE second

Closed transfer wherever possible. Local exhaust ventilation at every open-handling point - drum opening, charging, weighing, sampling. Airborne dust must be captured at source; general room ventilation is not adequate for a sensitiser.

PPE: chemical-resistant gloves, sealed goggles or face shield (H318 - serious eye damage), coveralls, and respiratory protection appropriate to the measured exposure for any open handling. PPE is the last line, not the control strategy.

Health surveillance: put exposed operators on a respiratory health programme with baseline and periodic assessment. Anyone who develops work-related wheeze, cough, chest tightness or rhinitis should be assessed promptly and removed from exposure pending investigation - early removal is what preserves lung function in anhydride-induced occupational asthma.

📁 Shipped with every consignment:

📄 EU CLP-format SDS, 16 sections, GHS Rev. 9 - with the H334 sensitiser section written properly, not boilerplated

📄 Batch COA from CNAS-accredited laboratory, including the full metal ion suite and particle size distribution

📄 REACH registration confirmation and TSCA inventory confirmation

📄 RoHS / REACH SVHC statement and non-GMO / non-animal-origin declarations on request

📄 Sample handling and dust-control guidance note for first-time users

Q1. Is this grade suitable for flexible printed circuit polyimide film?

The parameters that decide it are all in range: moisture 238 ppm, free acid 0.10%, TMA 0.02%, DMF-insolubles 13.6 ppm, and Cu/Ca/Na/K non-detect. That said, no supplier can qualify your film for you - casting equipment, imidisation profile and diamine source all interact. Take a qualification sample, run your own PAA viscosity build and film tensile test, and only then commit. We will supply retained-sample data from adjacent lots to support the qualification.

Q2. PMDA or TMA - which anhydride do I need?

They are not substitutes. PMDA is tetrafunctional (two anhydride rings) and builds fully aromatic polyimide. TMA is trifunctional (one anhydride ring plus one free carboxyl) and builds polyamide-imide, polyester resins and trimellitate esters. PMDA gives higher thermal performance and stiffness; TMA gives better solubility and processability. If your target is a Kapton-type film you need PMDA; if it is Torlon-type PAI or a wire enamel with solution processability, TMA.

🔗 Full comparison: TMA vs PMDA →

Q3. My last lot gave low poly(amic acid) viscosity. Is that the PMDA?

Often, but not always. Check in this order: (1) PMDA moisture and free acid on the actual drum used, not the COA - hydrolysis after opening is the most common cause; (2) diamine purity and its own moisture; (3) solvent water content, since wet NMP hydrolyses PMDA in the reactor faster than anything that happened in storage; (4) stoichiometric weighing accuracy; (5) TMA content as a chain terminator. Send us the failing lot number and your PAA viscosity data and we will pull the retained sample and retest.

Q4. Can PMDA be dried and recovered if it has picked up moisture?

Partially, and with caution. Pyromellitic acid can be re-dehydrated back to the dianhydride at elevated temperature under vacuum, but PMDA also sublimes readily, so the operation loses material and needs proper condensing. In practice most film producers reject out-of-spec lots rather than reprocess them, because the residual free-acid figure after recovery is hard to guarantee. For non-critical applications such as PET chain extension, gentle vacuum drying is more often worthwhile. Ask us before attempting it.

Q5. How is the respiratory sensitisation risk handled in practice at customer plants?

The plants that manage it well do three things: closed or semi-closed transfer with LEV at every opening point; a documented respiratory health surveillance programme for exposed operators; and a low threshold for investigating symptoms rather than waiting for them to worsen. Coarse, free-flowing powder such as this grade helps, because it generates far less airborne dust than a milled fine powder - but it does not remove the requirement.

🔗 The same class of controls applies to trimellitic anhydride: Anhydride Safety & Respiratory Sensitisation →

Q6. What volume can you actually commit to, and what is the lead time?

Qualification samples of 1–5 kg ship in nitrogen-sealed foil packaging with a full COA. Commercial supply currently runs against a commissioned 3,000 t/a line, so annual programmes above a few hundred tonnes need allocation confirmed before we quote a price - we will tell you honestly if the volume is not available rather than take the order and disappoint you. Send target annual volume, destination port, grade requirement and required documentation set, and we will come back within 24 hours.

📩 Request PMDA Price, Qualification Sample & COA

Tell us your application (PI film / PI varnish / epoxy hardener / PET chain extension / ester synthesis), target annual volume, destination port, and the parameters your specification is written against. We reply within 24 hours with pricing, a representative batch COA including the metal ion suite and particle size distribution, EU CLP SDS, and the dust-control handling note. Qualification samples 1–5 kg in nitrogen-sealed foil packaging.