Polyethylenimine (PEI) or polyaziridine is a polymer with repeating unit composed of the amine group and two carbon aliphatic CH2CH2 spacer. 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. 

Branched polyethylenimine (BPEI) is a polymer with repeating units composed of ethylene diamine groups. BPEIs contain primary, secondary and tertiary amino groups. Primary amines on the BPEI are used to covalently link BPEI to carboxyl functionalized nanoparticles to generate a robust BPEI surface that is highly positively charged.

Uses

Branched polyethylenimine acts as an auxiliary agent. It is used in paper-making, water treatment, detergents, adhesives and cosmetics. 

It acts as an auxiliary agent intensifying manufacturing processes and improving quality of the final products. Extensively investigated as non-viral vector carriers.