Effect of the polymer matrix structure of reticular poly(vinylpyridines) on their electron‐donor properties

Abstract

SYNOPSISThe effect of the polymeric matrix structure on the acidic-base, coordination, and kinetic properties of reticular poly (vinylpyridines) (RPVPs) obtained by copolymerization of 4vinylpyridine (AH-40) and 2-methyl-5-vinylpyridine (AH-25) with divinyl aromatic compounds has been investigated by potentiometric as well as by IR and EPR spectroscopic met hods.The increase in the content of the crosslinking agent results in a lower pK, of RPVP and in reduced stability constants of their complexes with transient metal ions; therefore, the defectiveness of the coordination centers is increased.The nature of the crosslinking agent determines the flexibility of the polymeric matrix and the availability of electron-donor groups in them affects the structure of the average statistical coordination center, thus bringing about a change in the RPVP electron-donor properties and in the stability constant of the polymeric complex. 309

Factors driving the protonation of poly(N‐vinylimidazole) hydrogels

“…The complexity of a swollen hydrogel is probably quite distant from ideality, but given the difficulty of calculating the activity coefficients, it is usually thought that (1) a highly swollen hydrogel may be approximated by a dilute polymer solution2 in such a way that γ Im is assumed to be equal to 1 and (2) log(γ ImH+ ) depends on the square root of the ionic strength and, in solutions without supporting electrolytes, approaches zero; therefore, the term log(γ Im /γ ImH+ ) is not taken into account in eq 5 38, 40. pH g may be substituted2, 3, 32–34, 37–39 by pH S , the equilibrium pH measured in the bath because pH g may not be determined. By the extrapolation of p K a values to α = 0, p K 0 , the negative logarithm of the intrinsic dissociation constant of the protonated form, can be determined: where R is the gas constant and T is the temperature.…”

“…The acid–base properties of soluble polymers, measured by p K a , have been broadly studied,14–31 and a few of these studies have been focused on sPVI 14–18. On the contrary, studies on p K a of swellable crosslinked polymers in centimeter‐size slab gel samples32–37 or microspheres38–40 are rarely found, and as far as we know, there is no study with respect to the basicity of hPVI. We consider first several well‐established facts concerning p K a of soluble polymers, including sPVI, to later summarize what is currently known about the ionization of crosslinked polymers.…”

“…If the ionization of soluble polyelectrolytes is a complex phenomenon, the protonation of a crosslinked swellable but insoluble hydrogel is even more complex. An increase in the crosslinker ratio ( C ) lowers p K a of basic crosslinked copolymers32 and increases p K a of acid crosslinked copolymers 33, 36. Crosslinked copolymers of acrylic acid33 or methacrylic acid34 are much less acidic (larger p K a ) than linear soluble copolymers.…”

Acrylic three-dimensional networks. II. Behavior of different acrylic ion exchangers in the retention and elution processes of some metal cations

“…From the literature data the chelating properties of the primary, secondary, and tertiary amine groups grafted on linear and crosslinked polymers are well known 2–8…”