Hydrogen-bonded multilayers of poly (carboxybetaine)s
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abstract
Using a layer-by-layer (LbL) sequential adsorption technique, we studied the construction of hydrogen-bonded multilayers of a weak polycarboxybetaine (poly-N--carboxypentyl-4-vinylpyridinium bromide (PCB5)) with poly(N-vinylcaprolactam) (PVCL). Self-assembly occurred at low pH values where carboxylic groups of PCB5 units were protonated and capable of binding with hydrogen-accepting groups of PVCL. Multilayers could not be constructed, however, in 0.01 M buffer solutions at pH 2.5, and potassium halide salts were required to promote multilayer deposition. Concentrations of halide salts at which deposition of PCB5/ PVCL multilayers occurred decreased in the series KCl > KBr > KI, following the Hofmeister series for binding of anions with PCB5 chains. Using a N-vinylcaprolactam copolymer which contained amino groups (PVCL-NH2), PCB5/PVCL-NH2 multilayers were constructed and covalently cross-linked, producing surface-attached hydrogels. The hydrogels showed typical polyelectrolyte salt-induced contraction at pH 2.5, where PCB5 units were cationic, but "antipolyelectrolyte" behavior, i.e., swelling in salt solutions at pH 7.5, where PCB5 units were zwitterionic. PCB5/PVCL-NH2 surface hydrogels were resistant to adsorption of negatively charged proteins and heparin at pH 7.4 in 0.15 M NaCl solutions. The produced PCB5/PVCL films and cross-linked PCB5/ PVCL-NH2 surface hydrogels might find applications as erasable films or as zwitterion-containing bioinert coatings, respectively. 2007 American Chemical Society.
