Temperature dependence of the binding of methyl orange by crosslinked poly(4-vinylpyridine)

Abstract

Various crosslinked poly(4-vinylpyridines) (CP4VP) with different degrees of crosslinking were prepared by radical copolymerization of 4-vinylpyridine with N, N′-tetramethylenebisacrylamide as crosslinker. The binding abilities of these crosslinked polymers were investigated at various temperatures in a buffer solution of pH 7. The first binding constant ( K 1) and thermodynamic parameters were evaluated from the equilibrium amounts of binding. The first binding constants showed bell-shaped curves when plotted against both the binding temperature and the degree of crosslinking. Lower temperature and higher degree of crosslinking at maximum binding in these bell-shaped curves were observed for this binding system when compared with those of the previously reported binding system (CP4VP/methyl organe) containing CP4VP prepared using N, N′-methylenebisacrylamide as crosslinker. The values of the enthalpy and entropy change increased on increasing the degree of crosslinking and decreasing the binding temperature, whereas the absolute magnitude of the free-energy change was not increased. These results could be accounted for in terms of the temperature dependence of the hole size of CP4VP in addition to the hydrophobic interactions in the binding process.