Surface properties of polyamidines

Aromatic and aliphatic polyamidines of the common structure -(R-1-N = C(R-2 )-NH)(n)- were investigated by electrokinetic measurements in dependence on the pH value. It could be evidenced, that all polyamidine surfaces show Br onsted basic behaviour. pK(A) values of the surfaces between 7 and 11 were calculated. Particularly, the aliphatic polyamidines (R-1, R-2 = alkyl) has proven to be strongly basic. The surface properties correlate well with th e basic behaviour of the polyamidines in solution. Furthermore, the surface charge density of the different solid substances was determined. It was fo und that in the case of aromatic polyamidines (R-1 = aryl) the charge densi ty is dependent on specific interactions of the amidine groups in the solid phase. Especially, in polyformamidines mutual shielding of the amidine gro ups by hydrogen bonds resulted in reduced charge densities on the surface. (C) 2001 Elsevier Science B.V. All rights reserved.