Ethylene imine polymer (polyethyleneimine, PEI) is a versatile cationic polymer with reactive amine groups. It is widely used as a flocculant in water and wastewater treatment to remove suspended solids, oils, and organic matter. In paper manufacturing, it serves as a dry-strength agent and retention aid to improve paper quality. In the textile industry, it enhances dye fixation and fabric finish. It is applied in oil recovery processes to facilitate the separation of oil from water. Additionally, it functions as an additive in adhesives and coatings, and as a crosslinking agent in resins, leveraging its reactive amine groups for improved adhesion and chemical resistance. PEI exhibits biocidal properties, making it suitable for antimicrobial treatments in industrial systems. In the chemical industry, it acts as an intermediate for synthesizing other chemicals requiring amine-functionalized structures. It is also employed in polymer synthesis to bind biomolecules such as proteins or nucleic acids, with applications in biological research and biotechnology, including gene delivery and the development of vectors for gene therapy.