Polyethyleneimine (PEI) – CAS 9002-98-6

Polyethyleneimine (PEI): Properties and Applications

1. Introduction

Polyethyleneimine (PEI) is a cationic polymer with a high density of primary, secondary, and tertiary amine groups. This unique structure provides strong positive charge, excellent adhesion, and the ability to form stable complexes with negatively charged molecules. PEI is widely used in water treatment, paper manufacturing, adhesives, textiles, and biomedical applications, including gene delivery and enzyme immobilization.

2. Chemical Structure and Types

Molecular formula: (C₂H₅N)ₙ

CAS number: 9002-98-6

Structure: PEI consists of repeating –CH₂–CH₂–NH– units. It is available in two main forms:

• Linear PEI: Contains predominantly secondary amines with primary amines at chain ends.

• Branched PEI: Contains primary, secondary, and tertiary amines, providing higher charge density and different physicochemical properties.

Molecular weight: Ranges from several hundred to several million Daltons, significantly affecting viscosity, solubility, and toxicity.

3. Physicochemical Properties

Appearance: Colorless to yellowish liquid (low MW) or waxy solid (high MW).

Solubility: Highly soluble in water; soluble in alcohols (ethanol, isopropanol) and some polar solvents.

pH: Aqueous solutions are alkaline due to protonation of amine groups.

Hygroscopic: Absorbs moisture from the air due to hydrophilic amine groups.

Cationic nature: At physiological pH, most amine groups are protonated, enabling strong electrostatic interactions with negatively charged surfaces and molecules.

4. Applications

Water treatment: Used as a flocculant and coagulant to aggregate suspended particles and accelerate sedimentation in wastewater treatment.

Paper industry: Improves paper strength by enhancing fiber bonding. Acts as a retention aid for fillers and dyes.

Adhesives and coatings: High amine content provides strong adhesion to metals, glass, and polymers. Used in adhesives, resins, and paints.

Biomedicine:

• Gene delivery (transfection): Branched PEI forms polyplexes with DNA or RNA, facilitating cellular uptake. Used in gene therapy research.

• Enzyme immobilization: Stabilizes enzymes through covalent or ionic binding, improving biocatalyst stability.

• Vaccines and nanoparticles: Acts as a stabilizing and delivery component.

Catalysis and chemical processes: Used as a base for functionalized materials (e.g., nanoporous sorbents for CO₂ capture and heavy metal removal).

Textile industry: Used in textile finishing for improved dye uptake and fabric properties.

5. Mechanism of Action

Flocculation: Positively charged PEI chains adsorb onto negatively charged colloidal particles, causing aggregation and precipitation.

Adhesion: Amine groups form hydrogen bonds and ionic pairs with functional groups on surfaces, enhancing adhesion.

Gene delivery: Forms polyplexes with nucleic acids, protecting them from nuclease degradation and facilitating cellular uptake via endocytosis.

6. Safety and Toxicology

Toxicity: PEI toxicity is related to its cationic nature, which can disrupt cell membranes. Higher molecular weight and branching generally increase cytotoxicity.

Irritation: May cause skin and eye irritation; handle with protective equipment.

Biocompatibility: Modified forms (pegylation, acetylation) are being developed to reduce charge density and toxicity for medical applications.

Occupational safety: Use gloves, safety goggles, and adequate ventilation when handling concentrated solutions.

7. Regulatory Status

PEI is listed under CAS 9002-98-6. It requires Safety Data Sheets (SDS) for industrial use. For biomedical applications (transfection, pharmaceutical development), compliance with GMP standards and regulatory approval is required.

8. Research and Development Prospects

Gene delivery optimization: Development of modified PEI derivatives (block copolymers, nanoparticles) to reduce cytotoxicity and improve cell specificity.

CO₂ capture: PEI immobilized on porous supports for low-temperature CO₂ adsorption in green technologies.

Enzyme stabilization: Continued research on PEI for enzyme immobilization in bioreactors, improving thermostability and pH tolerance.

Smart materials: Combination of PEI with other polymers and nanoparticles for pH-responsive or ion-sensitive coatings.

9. Conclusion

Polyethyleneimine (PEI, CAS 9002-98-6) is a versatile cationic polymer with high amine content, enabling strong electrostatic interactions and complexation with negatively charged molecules. Its applications span water treatment, paper manufacturing, adhesives, and biomedicine, particularly in gene delivery. While PEI offers significant advantages, its toxicity increases with molecular weight and branching, necessitating careful formulation and handling. Ongoing research focuses on reducing cytotoxicity, improving biocompatibility, and expanding its functional capabilities in emerging technologies.