INTERACTION OF CROSS-LINKED POLY(4-VINYLPYRIDINE) WITH METHYL-ORANGE

Various crosslinked poly(4-vinylpyridine)s (3) having different degrees of crosslinking were prepared by the radical copolymerization of 4-vinylpyridine (1) with N,N'-hexamethylenediacrylamide (2) as a crosslinker. These crosslinked polymers were examined for their ability to bind methyl orange at various temperatures in a buffer solution of pH 7. The first binding constants (K1) and thermodynamic parameters that accompany the binding were evaluated. The values of K1 show bell-shaped curves against both the binding temperature and the degree of crosslinking of 3. Lower temperature and higher degree of crosslinking for the maximum binding in the bell-shaped phenomenon of this binding system were observed, when they were compared with those of the previously reported binding systems, 1/N,N'-methylenediacrylamide copolymers-methyl orange and 1/N,N'-tetramethylenediacrylamide copolymers-methyl orange. The values of enthalpy change and entropy change increase with increasing degree of crosslinking of 3, whereas the absolute magnitude of free energy change is not increased. These results could be accounted for in terms of the temperature dependence of the hole size of 3 rather than the hydrophobic interaction in the binding process.