The dissociation and specific viscosity of polymethacrylic acid

Abstract

Solutions of polymethacrylic acid have been partially neutralized tc different extents, and the p H values and viscosities of the resulting solutions determined. These measurements were carried out at several different potassium ,chloride concentrations, and on several polymer samples. The calculated dissociation constants of the polymer acid were substituted in the equation developed by J. Th. G. Overbeek, which expresses the change in dissociation constant of a polybasic acid as a function of the radius of the molecular coil and of the charge on the molecule. The derivation of this equation treats the polymer molecule as a sphere containing a continuous charge. The radii found are of the right order and change in the expected way with changing ionic strength and ionisation. Substitution of these radii in the Debije viscosity equation gives satisfactory agreement between observed and experimental viscosities at low degrees of ionisation. At higher degrees of dissociation it would seem that the treatment of the polymer coil as a sphere is no longer satisfactory, although a better approximation is obtained if the charge is considered to be entirely on the surface of the sphere.

Dissociation of Carboxyl-Terminated Cascade Polymers: Comparison with Theory

“…The pH of a polyacid solution can be generally described by 23,24 where pK o , the intrinsic dissociation constant, is obtained by extrapolating pK a to R ) 0, and (dG el /dR) is the electrostatic Gibbs free energy change per unit degree of dissociation. where n is the electrolyte concentration, the dielectric constant here set at 78.5, and k the Boltzmann constant.…”

Protonacijske ravnoteže linearnih homopolikiselina

“…2,[22][23][24] Razlike između prividnih konstanti deprotonacije pri različitim α uglavnom su posljedica elektrostatskog odbijanja između nabijenih skupina na polielektrolitnom lancu.…”

“…22,23 Za procjenu ψ 0 pretpostavili su da proton disocira iz unutrašnjosti domene poliiona, koja se može smatrati sferom s uniformno raspoređenim, nabijenim segmentima. U slučaju polikiselina čiju su protonaciju istraži-li (poliakrilna kiselina, polimetakrilna kiselina), 22,23 slaganje predloženog modela s eksperimentalnim podatcima bilo je tek u ispravnom trendu ovisnosti pK ap (α).…”

“…Udjel navedenih regija može se smatrati proporcionalnim ukupnom broju parova neprotoniranih skupina, ukupnom broju parova protoniranih skupina te ukupnom broju parova protoniranih i neprotoniranih skupina. Prema Guggenheimovoj nultoj aproksimaciji za regularne smjese 40 moguće je pokazati da će uz navedene pretpostavke ovisnost prividnih konstanti ravnoteže biti dana jednadžbom (23). Međutim, valja reći da primijenjena približenja predstavljaju zaista gruba pojednostavljena protonacijske ravnoteže na poliionu.…”

“…Za spomenute kiseline pK ap (α) više nije približno linearna, kao u slučaju polikiselina kod kojih se funkcijske skupine nalaze na svakom drugom ugljikovom atomu, [20][21][22][23][24][25][26][27][28]32 već sigmoidalna s točkom infleksije pri α = 0,5.…”