From Propylene Oxide to Protected Circuits: The Petrochemical Raw Materials Behind Polyurethane Potting for EV Battery Electronics

The polyurethane potting raw materials that protect EV battery electronics begin in a refinery and a steam cracker. Propylene is oxidised to propylene oxide and polymerised into polyols; benzene and toluene are nitrated, reduced and converted into the isocyanates MDI and TDI; glycols, acids, solvents and plasticisers fill in the rest of the formula. When those two sides are mixed and poured around a battery management board, they cure into the tough, flexible shield that keeps moisture, vibration and coolant away from the circuit.

Every property engineers care about, from hardness and adhesion to pot life and electrical insulation, traces back to the quality and consistency of those petrochemicals. Understanding polyurethane potting raw materials is therefore as important as choosing the resin system itself. This guide from Chelora PetroChem, which supplies petrochemicals across the olefin, aromatic and glycol chains from Mumbai, follows each raw material from feedstock to potting compound, explains which specifications matter, and sets out how formulators can secure a stable supply.

Petrochemicals in the Polyurethane Potting Chain at a Glance

What Is a Polyurethane Potting Compound Made Of?

A polyurethane potting compound is made of two reactive parts, a polyol side and an isocyanate side, which are mixed in a fixed ratio just before use. The polyol side usually also carries fillers, catalysts, pigments and additives, so it makes up most of the formulation by weight.

Among polyurethane potting raw materials, the polyol, often labelled Part A, supplies hydroxyl groups. The isocyanate, Part B, supplies NCO groups that react with those hydroxyls to form urethane links. Formulators balance the two using the NCO index, the ratio of isocyanate groups to reactive hydrogen, so that the cured resin reaches the intended hardness without leftover unreacted material. Choosing the polyol sets much of the character of the cured potting: long, low-functionality polyether chains give soft, flexible elastomers, while shorter or higher-functionality polyols give harder, more rigid compounds. The isocyanate sets reactivity, strength and how the compound handles heat.

How Do Polyether Polyols Start With Propylene Oxide?

Polyether polyols start with propylene oxide, which is added step by step onto a small starter molecule until the chain reaches the target length. They are the most widely used polyols in polyurethane, including many potting grades.

Producers begin with a starter containing hydroxyl groups, such as mono propylene glycol or diethylene glycol for two-armed diols, or glycerol for three-armed triols. In the presence of a catalyst, traditionally potassium hydroxide and increasingly double metal cyanide catalysts, propylene oxide rings open and add onto each arm. Stopping at a low molecular weight gives a hard, highly crosslinked resin; growing long chains gives a soft, rubbery one. Many producers also cap the chains with ethylene oxide so that they end in primary hydroxyl groups, which react faster with isocyanate and let formulators shorten cure times without heavy catalyst loadings.

Propylene oxide itself is made from propylene, a product of steam crackers and refinery units, by several routes including the chlorohydrin process, co-product processes and direct oxidation with hydrogen peroxide.

Where Do Polyester and Castor Oil Polyols Fit?

Polyester and castor oil polyols fit where formulators need properties that polyethers do not give as easily, such as stronger adhesion, better solvent resistance or low moisture uptake. Many electronic potting compounds blend more than one polyol type.

Polyester polyols are made by condensing a dicarboxylic acid or anhydride with a glycol. Adipic acid and phthalic anhydride are common acid components, combined with glycols such as mono ethylene glycol, diethylene glycol or propylene glycol. Polyester-based compounds tend to bond strongly and resist oils and solvents, but they are more prone to hydrolysis in hot, humid conditions than polyethers, which matters inside a battery pack that may see condensation.

Castor oil polyol is a natural alternative with a long history in electrical potting. Castor oil is a triglyceride rich in ricinoleic acid, which carries a hydroxyl group on its chain, so it can react directly with isocyanates. Compounds based on castor oil are valued for low water absorption, good hydrolysis resistance and electrical insulation. India produces most of the world's castor seed, largely in Gujarat, and accounts for the great majority of global castor oil exports, which gives Indian formulators a local, renewable polyol source to combine with petrochemical ones.

How Do Benzene and Toluene Become the Isocyanate Side?

Benzene and toluene become the isocyanate side through a sequence of nitration, reduction and phosgenation that converts them into MDI and TDI, the two most important aromatic isocyanates.

For MDI, benzene is nitrated with nitric acid to nitrobenzene, which is hydrogenated to aniline. Aniline is then condensed with formaldehyde to give methylene dianiline, and phosgenation converts it into a mixture of monomeric and polymeric MDI. For TDI, toluene is nitrated to dinitrotoluene, reduced to toluenediamine and phosgenated. Electronic potting compounds most often use MDI, either as polymeric MDI or as prepolymers, because it has a much lower vapour pressure than TDI and is easier to handle safely at the dispensing line.

This isocyanate chain is highly concentrated. A small number of large global producers operate most of the world's MDI capacity, and India relies heavily on imports of MDI while producing some TDI domestically. NITI Aayog's 2025 roadmap for the chemical industry listed MDI and TDI among technologies India needs to access. For Indian potting compound makers, that means the isocyanate side is usually the part of the formula most exposed to international price swings and shipping delays.

What Role Do Solvents, Plasticisers and Glycols Play Around the Potting Line?

Solvents, plasticisers and glycols play supporting roles around the potting line: they clean equipment, adjust the softness of some compounds and, in the case of glycols, form the coolant that potting is often meant to keep away from electronics.

Methyl ethyl ketone and ethyl acetate are widely used to clean meter-mix-dispense equipment and to degrease housings and boards before potting, because good adhesion depends on a clean, dry surface. In softer potting compounds and sealants, plasticisers such as dioctyl terephthalate (DOTP) can lower hardness and viscosity; non-phthalate plasticisers are increasingly preferred because several ortho-phthalates are restricted in Europe. Around the battery itself, ethylene glycol-water mixtures circulate as coolant through plates beside the cells, which is one reason battery management electronics near those plates are potted rather than merely coated. Further upstream in battery making, N-methyl-2-pyrrolidone (NMP) is used as the solvent for electrode slurries in lithium-ion cell production.

Which Properties of Polyurethane Potting Raw Materials Decide Performance?

The properties of polyurethane potting raw materials that decide performance are those that control stoichiometry, reactivity and electrical behaviour. Small drifts in any of them can change pot life, hardness or insulation even when the product name on the drum stays the same.

For polyols, the key figures are hydroxyl value, which sets how much isocyanate is needed; functionality, which governs crosslink density; viscosity, which affects mixing and flow around components; acid value and residual alkalinity, which can speed up or slow down the cure; water content; and colour. For isocyanates, NCO content and viscosity are the headline numbers, along with acidity and any hydrolysable chlorine that can influence reactivity. For solvents and plasticisers, purity, water content and ionic contamination matter because residues on a board can reduce insulation resistance. Consistent certificates of analysis, checked against the formulator's own incoming tests, are what keep a potting line stable from one batch to the next.

Why Does Feedstock Volatility Matter for EV Battery Electronics?

Feedstock volatility matters to makers of EV battery electronics because the cost and availability of potting compounds move with propylene, benzene and isocyanate markets, which can swing quickly when crude oil prices change or a large plant has an outage.

Propylene and benzene prices follow naphtha, crude oil and the operating rates of crackers and reformers. Propylene oxide and MDI capacity is concentrated in relatively few sites worldwide, so an unplanned shutdown or a force majeure declaration at one plant can tighten supply across a region within weeks. Freight disruption on major sea routes adds a further layer of risk for importing countries. Potting compound makers usually respond by holding safety stock, qualifying more than one grade or supplier for each critical raw material, and agreeing scheduled deliveries with their suppliers. For battery and electronics manufacturers, asking a potting supplier how it secures its polyurethane potting raw materials, and how dependable its petrochemical supply is, should be a standard part of supplier assessment.

How Is India Building Its Own Polyurethane Feedstock Base?

India is building its own polyurethane feedstock base gradually, with strong positions in some links of the chain and continued import dependence in others. For buyers of polyurethane potting raw materials, knowing which is which helps decide where to hold stock and where local supply is reliable.

Domestic refining and cracking capacity supplies benzene, toluene, propylene and ethylene, and India produces glycols, phthalic anhydride and several solvents at scale. Castor oil gives the country a natural polyol advantage that few others share. The weaker links are propylene oxide derivatives and, above all, MDI, where supply still depends heavily on imports from a small number of global producers. Large Indian petrochemical groups have announced or studied new downstream projects, and government roadmaps have identified isocyanates as a priority, but these take years to build.

In practice, Indian formulators of potting compounds for EV battery electronics tend to combine local glycols, solvents and castor-based polyols with imported isocyanates and specialty polyether polyols. That mix makes the isocyanate and polyether inputs the right place to focus safety stock and dual sourcing, while locally produced materials can often be bought on shorter cycles.

How Have Polyurethane Raw Materials Evolved?

Polyurethane raw materials have evolved from a narrow choice of polyester resins after the Second World War to a wide toolkit of engineered polyols and isocyanates, and that evolution is what makes today's specialised potting compounds possible.

Early commercial polyurethanes relied mainly on polyester polyols. During the 1950s, polyether polyols based on propylene oxide became available at scale and quickly took over much of the market, because they were cheaper, easier to process and more resistant to hydrolysis. Polymeric MDI was commercialised in the same period and became the backbone of rigid and cast polyurethanes. In the 1990s, double metal cyanide catalysts allowed producers to make long-chain polyether polyols with fewer unwanted by-products, improving the consistency of flexible and elastomeric grades. More recently, the hydrogen peroxide to propylene oxide (HPPO) process, first operated commercially in Europe in 2008, reduced the by-products of propylene oxide manufacture. Alongside these developments, castor oil has remained a trusted polyol for electrical applications, and interest in bio-based and recycled polyols continues to grow.

How Should Formulators Source Polyurethane Potting Raw Materials?

Formulators should source polyurethane potting raw materials by fixing tight specifications, qualifying more than one supply route for the most concentrated inputs, and planning deliveries around production. The six steps below provide a practical sequence.

1. Define the critical specifications.For each polyol, isocyanate, glycol, solvent and plasticiser, agree limits on the properties that control your process, such as hydroxyl value, NCO content, viscosity, acidity, colour and water content.
2. Map where each material comes from.Identify the producer and country behind every raw material, and mark the inputs, usually MDI and propylene oxide derivatives, that depend on only a few plants.
3. Qualify alternatives before you need them.Trial a second grade or supply route for each concentrated input, comparing pot life, cured hardness, adhesion and electrical results against your standard.
4. Control moisture from delivery to use.Specify packaging and closures that keep water out, test incoming lots, and store hygroscopic materials under dry conditions.
5. Agree scheduled supply.Share forecasts with suppliers and arrange contract or scheduled deliveries for high-volume inputs, which usually improves both price stability and priority during shortages.
6. Keep a documentation trail.File each raw material's CoA, SDS and batch number against the potting lot it went into, so that any field issue can be traced back quickly.

What Are Formulators Asking About Polyurethane Potting Raw Materials?

Continue reading