Salt-responsive polymers

The continuous phase in the ABS polymer is responsible for most of its chemical properties. Because of the presence of only C-C binding in the polymer chain no hydrolytic reactions can take place. ABS polymers are in general resistant to aqueous salt, base or acid solutions and are not dissolved by paraffinic hydrocarbons. Depend-... 

Salt-responsive polymers, which contain charged groups along the polymer chains, may be classified as polyelectrolytes or polyzwitterions. Polyelectrolytes contain anionic or cationic charges along or pendent to the polymer backbone, whereas polyzwitterions have both anionic and cationic charges (Fig. 3.10) [80]. 

FIGURE 3.10 Generalized structures of salt-responsive polymers. 

FIGURE 3 II Typical monomers for the synthesis of salt-responsive (co(polymers. 

Work on ion-conducting polymers started after it was reported during 1951 that salts can interact with PEO chains (Rg. 11.1) and the properties of polymer salt solutions were studied during the 1960s. Ionic conductivity in a PEO-alkaline metal ion complex was first reported by Wright in 1975. As the concentration of lithium salt was increased in the PEO, a general reduction in both the conductivity and number of lithium transfers was observed. The reduction was attributed to the motion of the polymer chains, responsible for ion mobility, being restricted and also formation of ion pairs. In turn, it lowered the number of free lithium ions available for conduction. Initial work was carried out by Armand as he realized that this... 

We are now in possession of the following information (1) the previously detected complex between and PEO in CD3OD has a pronounced effect on (2) a looser polymer-salt interaction, such as that responsible for salting out , in K2SO4-PEO-D2O solutions, has no apparent effect on (3) the salting-out interaction has a pronounced effect on solution viscosity. Complex formation may also affect polymer viscosity but it is difficult to separate its influence from the salting-out process. 

The results from EQCM studies on conducting polymer films can be ambiguous because the measured mass change results from a combination of independent ion transport, coupled ion transport (i.e., salt transport), and solvent transport. In addition, changes in the viscoelasticity of the films can cause apparent mass changes. The latter problem can be minimized by checking the frequency response of the EQCM,174 while the various mass transport components can be separated by careful data analysis.175,176... 

Another type of gel expands and contracts as its structure changes in response to electrical signals and is being investigated for use in artificial limbs that would respond and feel like real ones. One material being studied for use in artificial muscle contains a mixture of polymers, silicone oil (a polymer with a (O—Si—O—Si—) — backbone and hydrocarbon side chains), and salts. When exposed to an electric field, the molecules of the soft gel rearrange themselves so that the material contracts and stiffens. If struck, the stiffened material can break but, on softening, the gel is reformed. The transition between gel and solid state is therefore reversible. 

The first set of data is for oil production from 22 wells. A quaternary ammonium salt polymer clay stabilizer was utilized in five of the well treatments. Otherwise the 22 well treatment designs were identical. Use of the clay stabilizer in 5 well treatments resulted in a 131% production increase compared to a 156% increase after stimulation of 17 wells without clay stabilizer. Although the initial overall production response of the five clay stabilizer treated wells was less, the overall production decline rate was 4% per year compared to 16%/yr for the treatments which did not include the clay stabilizing polymer. This decline rate was determined for the period 4 to 24 months after well treatment. It is tempting to speculate that the lower initial production response of the five polymer treated wells was due to the formation of an adsorbed polymer layer which reduced formation permeability (particularly of the Wilcox Formation) significantly. 

The few examples of deliberate investigation of dynamic processes as reflected by compression/expansion hysteresis have involved monolayers of fatty acids (Munden and Swarbrick, 1973 Munden et al., 1969), lecithins (Bienkowski and Skolnick, 1974 Cook and Webb, 1966), polymer films (Townsend and Buck, 1988) and monolayers of fatty acids and their sodium sulfate salts on aqueous subphases of alkanolamines (Rosano et al., 1971). A few of these studies determined the amount of hysteresis as a function of the rate of compression and expansion. However, no quantitative analysis of the results was attempted. Historically, dynamic surface tension has been used to study the dynamic response of lung phosphatidylcholine surfactant monolayers to a sinusoidal compression/expansion rate in order to mimic the mechanical contraction and expansion of the lungs. 

Therefore, the coupling of polymer segments to the counterion cloud, which is directly responsible for the term N in the above equation, dominates the collective diffusion coefficient. Since Rg N for salt-free solutions, Df is independent of N. 

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

In a subsequent study by Robertson, Murphy, and coworkers, polymer 23 was synthesized by anodie polymerization on platinum electrodes and eompared to polymer 19 in order to determine the effect of the position of the linkage of the dithiolene to thiophene moieties. In this study, the researchers used the salts [Bu4N][ll] and [Bu4N][16] in MeCN to prepare the respective polymers 19 and 23. Surprisingly, the polymerization of the anion 11 resulted in films exhibiting different electroehemieal response than that observed for 19... 

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