Specific F- binding to phenyl ring of aromatic polymers

Most of the hydrogels deswell more remarkably in F- containing solutions than in other monovalent anion containing solutions. However, significant deswelling followed by abnormal reswelling of polymer gel in KF solutions with increasing F- concentration was observed in a series of polymer gels consisted of phenyl rings, for instance, poly(styrene sulfonic acid) (PSSA), hydroxypropyl methylcellulose phthalate (HPMCP) and poly(4-vinyl phenol) (P4VPh) gel. Driving force of this phenomenon was studied to reveal the specific interactions involved in the aqueous systems of aromatic polymers. Elemental analysis and XPS results suggest that F- is embedded to the gel by the physical adsorption of KF, as well as the interactions between phenyl ring and F-. Further theoretical calculations revealed that the interaction may be (phenyl)CH center dot center dot center dot F-(H2O)(n) interaction, which is stronger than (phenyl)CH center dot center dot center dot(H2O)(n) hydrogen bond. This kind of interaction decreases with the increasing water number and it is invalid when the surrounding water number is more than 5 for the phenol-F-(H2O)(n). system. Therefore, we conclude that F- could bind to phenyl ring via such (phenyl)CH center dot center dot center dot F-(H2O)(n) interaction in solutions with low hydrophilicity. The strong polarization effect of F- and (phenyl)CH center dot center dot center dot F-(H2O)(n) interaction are two important driving forces for the reswelling of gels. (C) 2009 Elsevier B.V. All rights reserved.