Polymer solutions dielectric constant

By measuring the static dielectric constant of solutions of polar polymers in nonpolar solvents, one may calculate a statistical mean dipole of the macromolecule. With polar solvents interesting information can be obtained concerning the interaction between polymer and solvent molecules. Finally the study of relaxation phenomena, including the accurate determination of the critical frequencies may lead us to a better knowledge of the statistical unit and of its interaction with its environment. 

Effect of copolymer composition on degradation rates of biodegradable polymer nanofibers. Concluded that conductivity or dielectric constant of solution determined fiber morphology. 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

The results obtained demonstrate competition between the entropy favouring binding at bumps and the potential most likely to favour binding at dips of the surface. For a range of pairwise-additive, power-law interactions, it was found that the effect of the potential dominates, but in the (non-additive) limit of a surface of much higher dielectric constant than in solution the entropy effects win. Thus, the preferential binding of the polymer to the protuberances of a metallic surface was predicted [22]. Besides, this theory indirectly assumes the occupation of bumps by the weakly attracted neutral macromolecules capable of covalent interaction with surface functions. 

When the reaction times for Step 1 are 5 min or longer, the samples severely crack, curl, or dissolve. These results suggest that substantial reaction is occurring in the bulk of the polymer. Significant hydrophilization can occur with reaction times as short as 5 s with RTD concentrations of 0.2-0.5 M. However, 0.002-0.02 M solutions of MeTD or PhTD do not allow sufficient reaction rates for surface hydrophilization at the shorter reaction times. Thus, diffusion of MeTD and PhTD into the polymer must occur readily from the acetonitrile solutions. Acetonitrile was used because it does not swell or dissolve the polymer or RTD-polymer adduct, and the RTDs are soluble and stable in it. This solvent is quite polar (dielectric constant, 38) (25), and this is probably a major factor in the partitioning of the relatively nonpolar RTDs between the polydiene film and the solvent. As noted below, more polar RTDs show less tendency to diffuse into the polymer. 

A new method for the syntheses of fluorocarbon polyarylate polymers has been demonstrated. The chemistry utilizes the [2jt+2rr] cyclodimerization of fluorinated olefins and generates polymers of novel composition. The first generation of polymers prepared by this method are polyarylate homopolymers. Theremoplastic polymers of high molecular weight can be achieved via neat or solution polymerization. One example of a thermoset polymer prepared by this method has a high Tg, low dielectric constant and dissipation factor, low moisture... 

Fluorinated poly(imide-ether-amide)s are readily soluble in organic solvents like dimethylformamide (DMF), N-methylpyrrolidone (NMP), pyridine or tetrahydrofu-ran (THF) and give flexible films by casting of such solutions. These polymers exhibit decomposition temperatures above 360°C, and glass transition temperatures in the 221-246° C range. The polymer films have a low dielectric constant and tough mechanical properties. 

Recently the synthesis and characterization of novel fluorinated poly(aryl ether)s containing perfluorophenylene moieties " " was also reported. These fluorinated polyethers were prepared by reaction of decafluorobiphenyl with bisphenols. These polymers exhibit low dielectric constants, low moisture absorption, and excellent thermal and mechanical properties. Tough, transparent films of the polymers were prepared by solution-casting or compression-molding. The fluorinated poly(aryl ether)s containing perfluorophenylene moieties are good candidates for use as coatings in microelectronics applications. 

In the mucosal environment, effects of salt, pH, temperature, and lipids need to be taken into consideration for possible effects on viscosity and solubility. A pH range of 4-7 and a relatively constant temperature of 37°C can generally be expected. Observed solution properties as a function of salt and polymer concentration can be referred to as saline compatibility. Polyelectrolyte solution behavior [27] is generally dominated by ionic interactions, such as with other materials of like charge (repulsive), opposite charge (attractive), solvent ionic character (dielectric), and dissolved ions (i.e., salt). In general, at a constant polymer concentration, an increase in the salt concentration decreases the viscosity, due to decreasing the hydrodynamic volume of the polymer at a critical salt concentration precipitation may occur. 

The fact that X for both salts lies in the range 0.20-0.25 shows that water in the membrane is a less effective solvent for ions than is bulk water i.e. the low-dielectric-constant matrix polymer lies well within the range of the electrostatic fields around the ions. Our value of Xg, the molar distribution coefficient of sodium chloride between polymer and solution, is in good agreement with values obtained by direct measurement (1,5,10, 11,12). This is further evidence in favour of our theories and assumptions. 

We wanted to be able to correct measurements of dielectric loss (conductance) and dielectric constant of polymerizing styrene solutions for whatever contribution arose from the dead polystyrene present in the solutions. What better way to make polystyrene that was free of all catalyst fragments and polar groups than to irradiate pure, dry styrene Using the same exhaustive drying technique that we were developing for our a-methylstyrene studies, we prepared a batch of pure, dry styrene. This was then to be irradiated under such conditions that approximately 15% conversion to polymer would occur. 

The most familiar method of evaluating is by dielectric dispersion experiments, in which the real and imaginary parts of the complex dielectric constant over those of the solvent are determined as functions of frequency. It is the value of referring to the state of vacuum that can be correlated with the molecular structure of the solute. Polymers cannot be dispersed in the gaseous state. Furthermore, solvents effective for polypeptides are usually polar, and only approximate theories are presently available for the estimate of vacuum < 2> from dielectric measurements with polar solvents. Therefore the dipolar information about polypeptides is always beset with ambiguity in absolute magnitude as well as in interpretation. 

Now we consider an experiment in which a static electric field is suddenly applied to a dilute polypeptide solution. If the rates of interconversions between helix and random-coil units are much faster than those of rotational motions of the entire dissolved polymer molecule as well as of local segments of it, there will be an increase in the dielectric constant which approaches a constant value (ds)ch with time t. This relaxation process is a kind of chemical relaxation, because the helix-coil interconversions responsible for it may be regarded as chemical reactions. Its detailed study should provide information about such elementary processes as those illustrated in Eqs. (E-13) and (E-15). This is Schwarz s basic idea. 

Samples of polyd,3-dioxocane) (-Ch OICf lsO-I and poly(1,3-dioxonane) [-Ch OICh lgO-] are prepared, and fractions of both polymers are studied in solution by means of dielectric constant measurements from 20 to 60°C. Mean-square dipole moments thus obtained are compared with theoretical results based on the RIS models of the two chains. Good agreement is obtained. 

Mean-square dipole moments of polylthiodiethylene gycol), an alternating copolymer of ethylene oxide and ethylene sulfide, are determined from dielectric constant measurements on dilute solutions of the polymer in benzene. Since the configuration-dependent properties of one of the parent homopolymers, PES, are unknown, because of its insolubility in ordinary solvents, the results are preferably compared with those of POE chains. It is found that the dipole moments of polylthiodiethylene glycol) are somewhat larger than those of POE. 

---