Solvation effects and reactivity of free pyridine residues in macromolecules of poly-4-vinylpyridine derivatives

Water-soluble derivatives of poly-4-vinylpyridine (PVP) were prepared by means of quaternization of PVP with ethyl bromide, butyl bromide, hexyl-bromide and bromacetic acid. In addition, hydrolysis of p-nitrophenylacetate (NPA) and 3-nitro-4-acetoxybenzoic acid (NABA) catalyzed by these polymers and 4-ethylpyridine as analogue were studied spectrophotometrically both in water and alcohol-water mixtures at 25° and pH 7·8.The second-order rate of NPA hydrolysis (K_t) was independent of the length of alkyl groups and the salt concentration. While an increase of the degree of quaternization (β) for PVP derivatives resulted in a reduction of the value of K_i in water, in 37–50 vol per cent alcohol-water there was the opposite effect. At large values of β, K_i did not depend on the content of ethanol.The bell-shaped dependence of K_i on β was shown in the case of amionic NABA. The value of K_i proved to be very sensitive to both the nature of salt and the salt concentration in aqueous solution.The use of viscosity, turbidimetry and potentiometry for studying these polymers allowed the role of the quaternized pyridine residue to be elucidated. The peculiarities of the kinetic behaviour of the free basic group were explained by the hydrophilic nature of the quaternized PVP changing as the degree of quaternization is increased so causing an exclusion of the substrate molecules from the polyion.