A titration technique has been used to directly measure the proton uptake b
y ion-exchange poly(2-vinylpyridine) coatings as a function of solution pH.
Contrary to the common assumption that each nitrogen in the pyridine ring
is attached to an H+ when the polymer film is fully protonated, the use of
the titration technique has shown that the portion of the pyridine sites ac
tually protonated does not exceed 25% anywhere in the pH range where the co
ating is stable. The pK(a) value for the poly(2-vinylpyridine) coating has
also been estimated to be 4.5 from the titration curve. (C) 2001 John Wiley
& Sons, Inc.