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

Various crosslinked poly(4-vinylpyridine)s (3) having different degree s of crosslinking were prepared by the radical copolymerization of 4-v inylpyridine (1) with N,N'-hexamethylenediacrylamide (2) as a crosslin ker. These crosslinked polymers were examined for their ability to bin d methyl orange at various temperatures in a buffer solution of pH 7. The first binding constants (K1) and thermodynamic parameters that acc ompany the binding were evaluated. The values of K1 show bell-shaped c urves against both the binding temperature and the degree of crosslink ing of 3. Lower temperature and higher degree of crosslinking for the maximum binding in the bell-shaped phenomenon of this binding system w ere observed, when they were compared with those of the previously rep orted 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 increa sing degree of crosslinking of 3, whereas the absolute magnitude of fr ee energy change is not increased. These results could be accounted fo r in terms of the temperature dependence of the hole size of 3 rather than the hydrophobic interaction in the binding process.