Vinylpyridine oxide copolymers: viscosity/pH relationship of aqueous solutions

Abstract

Complex variations with pH in the viscosity of poly(2-vinylpyridine 1-oxide) in aqueous solution have been observed and large changes in viscosity with small changes in pH at certain pH values have been related to conformational changes. A viscometer is described that allows the viscosity changes to be followed with greater accuracy. The new observations indicate that at some pH values the viscosity readings are not reproducible, probably because the change in viscosity is large over a pH range that is too small to measure accurately. This suggests that in passing from one extreme conformation to another the polymer passes through a highly unstable conformation. The variation of viscosity with pH has been studied for certain vinylpyridine oxide copolymers, namely poly(2-vinylpyridine 1-oxide- co-4-vinylpyridine 1-oxide), poly(2-vinylpyridine 1-oxide- co-2-methyl-5-vinylpyridine 1-oxide) and poly(4-vinylpyridine 1-oxide- co-2-methyl-5-vinylpyridine 1-oxide). The shapes of the viscosity/pH curves are interpreted in terms of the curves of the polymers formed from each comonomer.