Polyacrylates Fractionation

Water-soluble polymers and polyelectrolytes (e.g., polyethylene glycol, polyethylene imine polyacrylic acid) have been used successfully in protein precipitations, and there has been some success in affinity precipitations wherein appropriate ligands attached to polymers can couple with the target proteins to enhance their aggregation. Protein precipitation can also be achieved by using pH at ustment, since proteins generally exhibit their lowest solubility at their isoelectric point. Temperature variations at constant salt concentration allow for fractional precipitation of proteins. 

Hydration of polymeric membranes may be influenced by the chemical identity of the polymers. A hydrophilic polymer has a higher potential to hydrate than a hydrophobic one. Sefton and Nishimura [56] studied the diffusive permeability of insulin in polyhydroxyethyl methacrylate (37.1% water), polyhydroxy-ethyl acrylate (51.8% water), polymethacrylic acid (67.5% water), and cupro-phane PT-150 membranes. They found that insulin diffusivity through polyacrylate membrane was directly related to the weight fraction of water in the membrane system under investigation (Fig. 17). 

Figure 17 Effect of weight fraction of water on insulin permeability of highly swollen polyacrylate membranes. (Reprinted with permission from Ref. 56.)...

The humates present in soil are polyelectrolytes and bear some similarity to polyacrylic acid and polymethacrylic acid (49, 50). The molecular weight distribution for the humates is considerable fulvic acid fractions of 1,000 daltons have been isolated (51) while humic acid molecular weights obtained by gel chromatography are in the range 17,000 to 100,000 daltons according to the type of soil from which it was extracted (52). However, ultracentrifugation analysis indicates a molecular range of 2,000 to 1,500,000 daltons for humic acids (55). 

A polyelectrolyte solution contains the salt of a polyion, a polymer comprised of repeating ionized units. In dilute solutions, a substantial fraction of sodium ions are bound to polyacrylate at concentrations where sodium acetate exhibits only dissoci-atedions. Thus counterion binding plays a central role in polyelectrolyte solutions [1], Close approach of counterions to polyions results in mutual perturbation of the hydration layers and the description of the electrical potential around polyions is different to both the Debye-Huckel treatment for soluble ions and the Gouy-Chapman model for a surface charge distribution, with Manning condensation of ions around the polyelectrolyte. 

A series of slurries of high solids, dispersed ground calcium carbonate were prepared. Firstly, a sample of Carrara marble was ground without dispersant to a mean size of 0.5 fim. This was then filtered to a solids level of 76% (volume fraction 46%), before being thoroughly mixed with the required dose of sodium polyacrylate dispersant and adjusted to a constant solids level of 70%. Doses ranged from zero to 25mgg (2.5%) of calcium carbonate. Samples were then left for two days to reach a steady-state adsorption level. After this they were sheared and their viscosity (Brookfield RV, 100 rpm, spindle 3) was measured. 

It was reported53> that a PEO sample with Mw = 1.37 10 and Mw/Mn = 1.23 is not fractionated by polyacrylic acid. Obviously, even if some change in MWD does take place upon the binding part of such a narrowly distributed polymer in a polycomplex, it is difficult to be estimated. 

By what fraction would the specific volume of polyacrylic acid have to change keep the same degree of order, s, as a change of temperature from 140 to 145 °C ... 

It seems, however, that only polyanions are chiefly concerned in the interferon induction. Further polymers having anionic groups have been investigated besides poly(nucleic acid)s and co-(cyclopolymers) 8, for which a partial hydrolysis of the anhydride moiety is supposed. Thus, poly(vinylsulfonate)s or polyacrylates have been found to be active, but, polymethacrylates inactive. It has been shown that in the case of acrylic acid copolymers the molecular weight is also of importance in addition to the structure of the polymer chain and the fraction of carboxy groups. The influence of these various parameters has been discussed in detail by De Somer (45). 

In aqueous solutions of poly(acrylic acid), for instance, the carboxyl groups of the polymer can be neutralised by the hydroxide ions of sodium hydroxide. The fraction of the carboxyl groups neutralised is called the degree of ionisation a . For = 1, the polymer is called sodium polyacrylate. 

Fig. 20. The heats of mixing of 50/50 mixtures of a chlorinated paraffin with various oligomeric polyacrylates, plotted against the weight fraction of C=0 groups in the polyacrylate. Those polyacrylates with very low and very high C=0 group content are positive (unfavourable) which corresponds to the immiscibility of the respective polymers...

For another synthetic ( conventional") vinyl polyelectrolyte, sodium polyacrylate, Takahashi and Nagasawa (42) have measured the intrinsic viscosity of a number of fractions under G conditions (1.056 N NaBr at 15° C) and report 11.0 as the characteristic ratio value of that polymer [using the value 0 — 2.87 10 for the universal parameter in equation (1)]. Both the polyvinylsulfonate and polyacrylate samples used by Eisenberg and Woodside and by Takahashi and Nagasawa were however of the conventional type, and thus composed of chains of unknown tacticity. This fact makes it more difficult to compare the experimental values with those dedudble from theories based on... 

Polyacrylic acid was purchased from Polysciences, Inc., and used with no further purification. HA was obtained from lake sediments (Lake Bradford, FL), and isolated and purified as described earlier (72). Two different size fractions of HA were obtained by ultrafiltration, as described below. All kinetic studies were performed at 0.10 M ionic strength (adjusted by the addition of NaC104), and were buffered by the addition of acetate (acetic acid and sodium acetate, pH 4.2). Buffer concentrations were 0.01 M. TES (N-tris[hydroxymethyl]methyl-2-aminoethane sulfonic acid, pH 7.0) buffer was used to maintain hydrogen ion concentrations during humate fractionation. 

Solid-phase extraction devices and applications are evolving rapidly, and novel techniques that stretch the classical definition of SPE are becoming routine. Pawliszyn introduced solid-phase micro extraction (SPME) in 1989,5,14 and a commercial apparatus is available from Supelco (Bellefonte, PA). The SPME apparatus is merely a modified syringe that houses a fused silica optical fiber coated with an immobilized polymer film. The fiber can be exposed for extraction and then retracted for insertion or removal from the sample vial or instrument. Both manual and autosampler devices are available and each can be adjusted for proper fiber depth. Several coatings are available with varying thickness including polydimethylsiloxane, polyacrylate, polydimethylsiloxane/divinylbenzene, and carbowax/divinylben-zene. In contrast to SPE, which is an exhaustive extraction approach, SPME will extract only a fraction of an available analyte, hence it is not suitable for the isolation of impurities and degradants in most applications.15... 

MgAl,04 Darvan 821 A, derivative of polyacrylic acid volume fraction... 

This difference in solubility has been exploited to fractionate protein solutions. Polyacrylic acid was used to partially fractionate a mixture of four enzymes (2). Whey protein fractions have also been isolated by precipitation with CMC (3). 

Dosage. Protein Removal increases with polyelectrolyte dosage to an optimum, then decreases with further addition of polymer (6, 12, 13). The dosage requirement depends on the nature of the polyelectrolyte, the degree of ionization and the protein (1-3, 5, 12). Sternberg and Hershberger (2) have used the different affinities of proteins for polyacrylic acid to fractionate a mixture of four enzymes by successive addition of polymer. 

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