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Polyethylenimine is produced on an industrial scale and finds many applications usually derived from its polycationic character.
Polyethylenimine is a synthetic polymer composed of repeating ethylene amine units with a high density of amine groups along the backbone.
Polyethylenimine is commonly abbreviated as PEI and exists in branched and linear forms, which differ in molecular architecture and reactivity.
CAS Number: 106899-94-9
Molecular Formula: C6H18N4
Molecular Weight: 146.24
Synonyms: Aziridine, ETHYLENEIMINE, Ethylenimine, Ethylene imine, Azacyclopropane, Dimethyleneimine, Azirane, Aziran, Dihydroazirene, Dihydroazirine, 1H-Azirine, dihydro-, Dihydro-1H-azirine, Dimethylenimine, Aethylenimin (German), Aziridin (German), Ethyleenimine (Dutch), Etilenimina (Italian), Everamine, Montrek 6, Epamine 150T, Epomine 150T, Tydex 12, EI, UN 1185, EINECS 205-793-9, CAS 151-56-4, CHEBI:30969, DTXSID8020599, RefChem:596749, CCRIS 296, HSDB 540, BRN 0102380, UNII-54P5FEX9FH, MFCD00039669, SCHEMBL2267, SCHEMBL4070, CHEMBL540990, NSC-124034, NSC-124035, NSC-124036, NSC-134422, NSC-196335, STL168030, STR07159, Q409141, WLN /T3MTJ/, Poly(ethyleneimine), Polyethylenimine, Ethylene imine polymer, Polyethyleneimine solution, Polyethylenimine linear, Polyethylenimine branched, Poly(ethyleneimine) solution (50% water), Polyethylenimine, 50% (w/v) aqueous solution, Polyethylenimine Linear (MW 25,000), Polyethylenimine Linear (MW 40,000), Polyethylenimine branched (Mw 2,000), PEI, PEI-1, PEI-2, PEI-6, PEI-12, PEI-18, PEI-100, PEI-400, PEI-600, PEI-1000, PEI-1120, Dow PEI-6, Dow PEI-18, Dow PEI-600e, Montrek PEI-6, Montrek PEI-18, Montrek 1000, Epomine 1000, Epomine P 1000, Everamine 50T, Everamine 210T, P-1000, 49553-93-7Epomin=Polyethyleneimine;EPOMIN SP-006;Aziridine polymer with N-(2-aminoethyl)-1,2-ethanediamine;Nippon Shokubai Epomin SP-110;Nippon Shokubai Epomin SP-003;Nippon Shokubai Epomin SP-006;1,2-Ethanediamine, N-(2-aminoethyl)-, polymer with aziridine;1,2-Ethanediamine, N1-(2-aminoethyl)-, polymer with aziridine
Polyethylenimine or polyaziridine is a polymer with repeating units composed of the amine group and two carbon aliphatic CH2CH2 spacers.
Linear polyethyleneimines contain all secondary amines, in contrast to branched PEIs which contain primary, secondary and tertiary amino groups.
Totally branched, dendrimeric forms were also reported.
Polyethylenimine is typically supplied as a viscous liquid or solid depending on molecular weight and degree of branching.
Commercial products may be listed as PEI solution, Branched PEI, Linear PEI, or Polyamine resin in industrial catalogs.
Registry identifiers vary by grade, but common CAS numbers include 9002-98-6 for general PEI polymers.
Typical physical properties include strong alkalinity due to Polyethylenimine amine groups and high water solubility for low and medium molecular weights.
Density is usually around 1.03–1.10 g/cm³ for aqueous solutions, and viscosity increases sharply with molecular weight and concentration.
Thermal stability is moderate, with degradation generally starting above 200 °C depending on structure and impurities.
Polyethylenimine is widely used as a flocculant and coagulant in water and wastewater treatment to remove suspended solids and heavy metals.
It is used in surface modification, adhesion promotion, and as a primer layer to improve coating or nanoparticle attachment.
In biotechnology, PEI is commonly applied as a transfection agent for gene delivery due to its strong interaction with DNA and RNA.
In papermaking, PEI improves wet strength, retention of fillers, and fixation of dyes and pigments.
It is also used in CO₂ capture research as an amine-rich sorbent for gas adsorption and separation technologies.
In battery and materials research, PEI is applied as a binder, dispersant, or surface functionalization agent for electrodes and catalysts.
Polyethylenimine is corrosive and can cause severe skin and eye irritation due to its strong alkalinity.
Inhalation of aerosols or vapors may irritate the respiratory tract and prolonged exposure can cause chemical burns.
It is toxic to aquatic organisms and should not be released into the environment without proper treatment.
Protective gloves, goggles, and lab coats are required when handling PEI in laboratory or industrial environments.
Spills should be neutralized and absorbed with appropriate materials, and waste should be disposed of according to chemical regulations.
Storage should be in tightly closed containers away from acids, oxidizers, and reactive metals to prevent hazardous reactions.
The linear PEI is a semi-crystalline solid at room temperature while branched PEI is a fully amorphous polymer existing as a liquid at all molecular weights.
Polyethylenimine is soluble in hot water, at low pH, in methanol, ethanol, or chloroform.
Polyethylenimine is insoluble in cold water, benzene, ethyl ether, and acetone.
Polyethylenimine has a melting point of around 67 °C.
Both linear and branched Polyethylenimine can be stored at room temperature.
Polyethylenimine is able to form cryogels upon freezing and subsequent thawing of its aqueous solutions.[3]
Polyethylenimine is a water-soluble polymer made by the polymerization of ethyleneimine.
Polyethylenimine is not an entirely linear polymer; it has a highly-branched structure that contains primary, secondary, and tertiary amines.
Its features are listed below.
Polyethylenimine finds many applications in products like: detergents, adhesives, water treatment agents and cosmetics.
Owing to its ability to modify the surface of cellulose fibres, PEI is employed as a wet-strength agent in the paper-making process.
Polyethylenimine is also used as flocculating agent with silica sols and as a chelating agent with the ability to complex metal ions such as zinc and zirconium.
There are also other highly specialized PEI applications:
Polyethylenimine was the second polymeric transfection agent discovered, after poly-L-lysine.
Polyethylenimine condenses DNA into positively charged particles, which bind to anionic cell surface residues and are brought into the cell via endocytosis.
Once inside the cell, protonation of the amines results in an influx of counter-ions and a lowering of the osmotic potential.
Osmotic swelling results and bursts the vesicle releasing the polymer-DNA complex (polyplex) into the cytoplasm.
If the polyplex unpacks then the DNA is free to diffuse to the nucleus.
Polyethylenimine is a highly cationic polymer because almost every repeating unit contains a primary, secondary, or tertiary amine group.
The pKa values of these amine groups are distributed over a wide range, which allows PEI to remain partially protonated across a broad pH window.
This buffering capacity is known as the “proton sponge effect,” which is especially important in gene delivery applications.
Branched polyethyleneimine contains primary, secondary, and tertiary amines in roughly a 1:2:1 ratio.
Linear polyethyleneimine mainly contains secondary amines along the backbone with primary amines at chain ends.
These structural differences strongly influence toxicity, reactivity, solubility, and complexation behavior with metals and biomolecules.
Polyethylenimine forms strong complexes with metal ions such as Cu²⁺, Ni²⁺, Co²⁺, Fe³⁺, and rare-earth elements through chelation.
Because of this, it is used in hydrometallurgy, ion-exchange resins, and selective metal recovery from industrial effluents.
It is also applied in catalyst preparation to anchor metal nanoparticles onto oxide or carbon supports.
In polymer chemistry, Polyethylenimine is used as a crosslinker and reactive intermediate to synthesize epoxy curing agents, polyurethanes, and hydrogels.
It can be chemically modified by acetylation, alkylation, quaternization, or grafting to tune hydrophobicity and biocompatibility.
Such derivatives are used in drug delivery systems, antimicrobial coatings, and stimuli-responsive materials.
Polyethylenimine is effective as an antimicrobial agent because its positive charge disrupts negatively charged bacterial cell membranes.
It is incorporated into coatings, packaging films, and water filtration membranes to reduce biofouling.
However, this same mechanism contributes to cytotoxicity in mammalian cells at high concentrations.
In textile processing, Polyethylenimine is used to fix reactive dyes and improve color fastness on cotton and synthetic fibers.
In leather processing, it acts as a retanning and dye-fixing agent to improve softness and durability.
In oil and gas operations, PEI derivatives are used as scale inhibitors and corrosion inhibitors.
Polyethylenimine solutions are hygroscopic and readily absorb moisture and carbon dioxide from air.
Long-term exposure to air can change viscosity and pH due to CO₂ absorption and partial neutralization.
For this reason, containers should be tightly sealed and preferably stored under inert atmosphere for sensitive applications.
From a regulatory perspective, Polyethylenimine is not classified as a carcinogen, but it is considered hazardous due to corrosivity and aquatic toxicity.
Safety data sheets typically classify it as Skin Corr. 1B and Eye Dam. 1 under GHS.
Environmental discharge limits are strict because cationic polymers are particularly harmful to aquatic ecosystems.
Uses:
Polyethylenimine is a synthetic, water-soluble, linear or branched polyamine, cationic organic polymer for carbon dioxide capture, electronic and biomedical applications.
Polyethylenimine modified mesoporous adsorbents can be used to adsorb carbon dioxide.
It is considered a typical carrier material and is widely used in gene delivery systems for its ability to build complexes with DNA and support the release of endosomes through the "proton sponge effect".
Polyethyleneimine is used in water and wastewater treatment as a flocculant and coagulant to remove suspended solids, dyes, and heavy metal ions.
It improves solid–liquid separation and is effective even at low dosages because of its strong cationic charge density.
Polyethylenimine is also applied in sludge dewatering processes to increase filtration efficiency.
Polyethyleneimine is widely used in biotechnology and pharmaceutical research as a non-viral gene delivery and transfection agent.
It forms stable complexes with DNA and RNA, protecting nucleic acids and facilitating cellular uptake.
Polyethylenimine is commonly used for transient transfection in mammalian cell culture, especially in HEK and CHO cells.
Polyethyleneimine is used as an adhesion promoter and surface primer to enhance bonding between coatings and substrates such as metals, glass, and polymers.
Polyethylenimine is applied to modify surfaces of nanoparticles, carbon nanotubes, graphene, and oxide powders to improve dispersion.
It is also used as an interlayer in thin-film deposition and membrane fabrication.
Polyethyleneimine is used in paper and packaging industries to improve wet strength, filler retention, and fixation of pigments and inks.
It enhances paper durability and reduces loss of fine particles during processing.
It is also applied in cardboard and specialty paper products for strength enhancement.
Polyethyleneimine is used in textile and leather industries as a dye-fixing agent to improve color fastness and uniformity.
It enhances binding of anionic dyes to fibers and leather surfaces.
It also improves resistance to washing and abrasion.
Polyethyleneimine is used in gas separation and carbon capture research as an amine-rich sorbent for CO₂ adsorption.
It is often impregnated into porous supports such as silica or activated carbon to improve capture efficiency.
It is studied for low-temperature and low-pressure CO₂ capture systems.
Polyethyleneimine is used in catalysis and materials synthesis to stabilize metal nanoparticles and control particle size.
It acts as a chelating and capping agent during synthesis of catalysts and functional nanomaterials.
It is also used to anchor catalytic species onto supports.
Polyethyleneimine is used in battery, supercapacitor, and fuel cell research as a binder, dispersant, or surface functionalization agent.
It improves adhesion of active materials to current collectors and enhances electrode stability.
It is also used to modify separators and catalysts for improved electrochemical performance.
Polyethyleneimine is used in water purification membranes to introduce positive surface charge and improve rejection of negatively charged contaminants.
Polyethylenimine is applied in layer-by-layer (LbL) assembled membranes to control pore size and surface functionality.
It also enhances antifouling performance by reducing organic and microbial attachment.
Polyethyleneimine is used in drug delivery systems as a carrier for small molecules, proteins, and nucleic acids.
It can be conjugated with targeting ligands or biodegradable polymers to reduce toxicity and improve selectivity.
It is studied in cancer therapy, vaccine delivery, and intracellular protein transport.
Polyethyleneimine is used in antimicrobial coatings for medical devices, food packaging, and air filtration systems.
Its cationic nature disrupts bacterial membranes and reduces biofilm formation on surfaces.
It is often grafted onto polymers or surfaces to provide long-term antimicrobial activity.
Polyethyleneimine is used in inkjet inks, pigment dispersions, and paints as a dispersant and charge control agent.
It stabilizes nanoparticles and prevents aggregation of pigments in aqueous formulations.
It also improves print quality and color uniformity.
Polyethyleneimine is used in mineral processing and flotation as a selective collector or depressant for certain ores.
It interacts strongly with mineral surfaces, improving separation efficiency.
It is studied for recovery of rare earth elements and critical metals.
Polyethyleneimine is used in enzyme immobilization to attach enzymes onto solid supports for biocatalysis.
It provides multiple functional groups for covalent bonding and improves enzyme stability and reusability.
This is important in biosensors and industrial bioreactors.
Polyethyleneimine is used in epoxy and resin systems as a curing accelerator and amine hardener component.
It improves crosslink density and mechanical strength in some adhesive formulations.
It is also used in corrosion-resistant coatings.
Polyethyleneimine is used in soil stabilization and dust control by binding fine particles and reducing erosion.
It improves mechanical cohesion of soils in construction and mining areas.
Polyethylenimine is also studied for immobilization of heavy metals in contaminated soils.
Safety profile:
Polyethyleneimine is strongly alkaline and can cause severe skin burns and serious eye damage on contact.
Direct contact may lead to redness, blistering, and permanent tissue injury if not washed immediately.
Eye exposure can result in corneal damage and possible vision loss.
Inhalation of Polyethylenimine aerosols or mists can irritate the respiratory tract and cause coughing, sore throat, and shortness of breath.
High concentrations may lead to chemical pneumonitis due to corrosive effects on lung tissue.
Repeated inhalation exposure can increase the risk of chronic respiratory irritation.
Ingestion of polyethyleneimine is harmful and can cause burns to the mouth, throat, and gastrointestinal tract.
Symptoms may include nausea, vomiting, abdominal pain, and difficulty swallowing.
Severe cases may require immediate medical intervention.
Polyethyleneimine is toxic to aquatic organisms and can cause long-lasting effects in aquatic environments.
Its strong cationic nature disrupts cell membranes of fish, algae, and invertebrates.
Release into waterways without treatment is considered environmentally hazardous.
Polyethyleneimine can react violently with strong acids, oxidizing agents, and acid chlorides.
Such reactions may generate heat and potentially hazardous by-products.
Improper mixing can lead to container rupture or chemical splashing.
During thermal decomposition, Polyethylenimine may release toxic nitrogen-containing fumes.
These gases can include ammonia and other irritating vapors.
Proper ventilation is required when heating or processing the material.
