Polyethylene imine (PEI) particles were readily prepared via a simple microemulsion polymerization method using AOT as surfactant in commercially available gasoline with moderately high yield (-75%) depending on the MW of PEI. The aqueous solution of branched PEI crosslinked with divinyl sulfone (DVS), called c-PEI particles were in the size range of tens of nanometers to tens of micrometers and upon filtration the desired size range was readily obtained. The prepared c-PEI particles were highly positively charged depending on the used amounts of crosslinker and the extent of modifying agents such as alkyl halide for different purposes e.g., CH3I that can conveniently be used for the quaternization reaction. The prepared c-PEI particles were demonstrated to be very useful as antimicrobial materials, drug delivery materials, as a template for metal nanoparticle preparation, as a catalysis medium for the reduction of 4-nitrophenol (4-NP) to 4-amino phenol (4-AP), and for hydrogen generation from the hydrolysis of NaBH4. (C) 2013 Elsevier BM. All rights reserved.