Weak polyacid

This potential reflects itself in the titration curves of weak polyacids such as poly(acrylic acid) and poly(methacrylic acid) [32]. Apparent dissociation constants of such polyacids change with the dissociation degree of the polyacid because the work to remove a proton from the acid site into the bulk water phase depends on the surface potential of the polyelectrolyte. 

Weak polyacid-Strong scattering, Turbidity, IR 9/1 1/1 Low pH, High p... 

Weak polyacid-Weak analysis, X-ray diffraction, Various High and low pH,... 

Under acidic conditions, weak polybases (P2VP or PEI) are almost all protonated but a weak polyacid (PMAA) is scarcely dissociated. Thus, the complex of PMAA with the proton-accepting polymers (PEO or PVPo), which may form hydrogen bonds with PMAA, is preferentially formed. 

At neutral pH, both a weak polyacid and a weak polybase are partially ionized, resulting in the formation of the polyelectrolyte complexes. 

In one example polymer segment density profiles of weak polyacid brushes consisting of polymethacrylic acid (PMAA) chains were investigated as a function of the pH of the environment by means of multiple-angle ellipsom-etry [68]. The polymer brushes were prepared by surface-initiated polymerization of methylacrylic acid as described above. 

Fig. 21 Profiles of a surface-attached weak polyacid brush as obtained from FT analysis of ellipsometric data at different pH. The pH is given in the figure. Analysis of the same ellipsometric data by Fresnel modeling. Best fits to complementary error functions at different pH given in the figure. For more details see text...

Information about physicochemical and complexation properties of polyvinylsulfonic acid (PVSH) or, more correctly, polyethylenesulfonic acid (PESH) [11] is much less available than that of the polyamines. PVSH (or PESH) is a simple, strong polyacid (see Fig. 6.6), so that partial ionization and possible hydrolysis effects, encountered with weak polyacids and their salts (e.g., polyacryfic acid and its salts), do not complicate the picture [76]. Commercially available sodium salt, PVSNa, is a brittle hygroscopic solid, soluble in water, but insoluble in organic solvents (methanol, dioxane, etc.) [77]. Viscosity behavior of the alkali metal salts was studied by several groups [28, 52, 75-77], but data are too scattered to be trustworthy. The PVS polyanion shows a definite selectivity in ion binding with alkali Li, Cs metals in the presence of Na, K hah des [78]. 

In Figure 4 we first present some typical adsorption data as a function of time. These data, taken from Paris and Cohen Stuart [25] are for the adsorption of a hydrophobically modified, weak polyacid (carboxypullulan modified with 12% hydrophobic dodecyl groups) onto the neutral, hydro-phobic substrate polystyrene. Measurements were made at low pH (where the polymer carries hardly any charge) and in the absence of salt. In Figure 4 we plot T(f) as a function of cbt as explained above, this will make curves measured at varying cb coincide, provided the adsorption resistances do not explicitly depend on time. As can be seen, this is an adequate assumption over a range of polymer concentrations from 5 mg L 1 to 100 mg L 1 and and within experimental error the curves coincide nicely. 

In case the host chain is a weak polyacid or weak polybase, similar effects can be induced by changes of the pH value, suppressing the ionization of the single stranded blocks. For example, a PEC between Na-poly(meth-... 

The potential difference between the surface of a polyion and the region in which the potential is measured during pH measurements in the course of neutralization of a weak polyacid with standard base provides an experimental evaluation of this deviation term (0.8686 Zw) in such polymeric systems. The deviation from ideality of mobile ions at the site of the neutralization reaction is obtained from the well-known equation given below ... 

Spontaneous formation of interpolymer complexes with a weak polyacid (like PAA) can be observed below a certain pH value (critical pH). Aqueous solutions of both polymers were mixed. At a pH below 4.0 complexes were formed. Irradiation of the diluted complex-containing solution results in an intermolecular cross-linking of the complexes at low radiation doses. Irradiation at higher doses generates simultaneously more than one radical on a chain. The formation of covalent bonds... 

Biesalski M, Johannsmann D, Ruhe J. Synthesis and swelling behavior of a weak polyacid brush. J Chem Phys. 2002 117(10) 4988-94. 

The phase diagrams (Figure 56.4) made by Tsuchida for a weak polyacid poly(methyl acrylic acid) (PMAA) and a strong polycation shows the effect of the concentration of the PEC. At low pH, the PEC formation is more favorable in dilute solution, but not in concentrated solution. This is assumed... 

Tsuchida showed that in the case of PECs formed between weak polyacids and polybases, the hydrophobicity can influence the formation of PEC. The PEC formed between PMAA and 10,10-ionene was more than the PEC formed between polyfacrylic acid) (PAA) and 10,10-ionene as the PMAA is more hydrophobic than PAA. 

In the case of weakly ionizable PEs, the fraction of charged monomer units, a, is controlled by an ionization equilibrium and is affected by the local proton concentration and ionic strength. Weak polyacids such as poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA), or polybases such as PVP and poly(dimethyl-aminoethyl methacrylate)(PDMAEMA) are typical examples of these pH-sensitive or annealing PEs. 

Each monomer of a weak polyacid can be ionized via the dissociation of a hydrogen ion,. The degree of dissociation of such acidic monomer, a(r), depends on the local concentration of hydrogen ions, c + (r), via the mass action law ... 

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