Primary amine groups of branched poly(ethylene imine) (PEI) were functionalized with quaternary ammonium groups, alkyl chains of different length, allylic and benzylic groups in a one-step reaction, using a carbonate coupler. The structure of the obtained amphiphilic polymers was determined by means of 1H and 13C NMR spectroscopy. Depending on their hydrophilic/hydrophobic balance, the obtained polymers can be used as water-soluble disinfectants and for antimicrobial coating materials. The bactericidal properties of some of the amphiphilic polymers against Gram-negative and Gram-positive bacteria were investigated. Minimal inhibitory concentrations (log 4 reduction of bacterial growth) against Escherichia coli and Bacillus subtilis were determined in the range of 0.3-0.4 mg/mL and 0.03-0.04 mg/mL for water-soluble polymers. Glass slides coated with functionalized PEIs showed a reduction of colony forming units of at least 95%, at best 99.9%, against E. coli and B. subtilis.

Branched poly(ethylene imine) (PEI) with primary, secondary and tertiary amine groups in a ratio of 1:2:1 was specifically functionalized at the primary amine groups with quaternary ammonium groups and C 12 alkyl chains. This reaction was performed by treatment of PEI with functional cyclic carbonates, i.e. trimethyl-(2-oxo-[1,3]dioxolan-4-ylmethyl)-ammonium iodide (1) and (2-oxo-1,3-dioxolan-4-yl)methyl dodecylcarbamate (2), under mild conditions in aprotic dipolar solvents. For determination of the reaction conditions model reactions of the functional carbonates with primary amines were performed in different solvents including water. In the presence of water side-reactions, such as hydrolysis of the ethylene carbonate ring, take place and have to be avoided. The structure of the obtained polymers was studied by means of 1 Hand 13 C-NMR spectroscopy, and the thermal properties were determined by means of DSC and TGA measurements. The PEI-functionalized polymers with long alkyl chains and quaternary ammonium groups are suitable for coating negatively charged surfaces by polyelectrolyte interaction. Also, the bacteriostatic properties of some amphiphilic model compounds were determined; a total inhibition of Escherichia coli by 0.01 wt% aqueous solutions was observed.

Cationic amphiphilic polymers were prepared from PEI and functional ethylene carbonates bearing cationic, hydrophobic or amphiphilic groups. The polymers are designed to exhibit antimicrobial properties. In a one-step addition, different functional ethylene carbonates were added to react with the primary amine groups of PEI. The water soluble polymers were studied regarding their ability to form soluble aggregates. Their hydrodynamic radii, their inhibition potential against proliferation of E. coli and their hemolytic potential were determined. A structure-property relationship was established by analyzing the antimicrobial activity as a function of the ratio of alkyl to cationic groups, length of the alkyl chains, and molecular weight of the PEI.

Cover: Cationic amphiphilic polymers were prepared from poly(ethylene imine) (PEI) and functional ethylene carbonates bearing cationic or hydrophobic groups. These polymers are designed to exhibit antimicrobial properties. Further details can be found in the article by N. Pasquier, H. Keul, E. Heine, M. Moeller,* B. Angelov, S. Linser, and R. Willumeit on page 903.