Differential membrane osmometry

Differential membrane osmometry Degree of substitution Proton charge... 

Tables 3 6 give a survey of literature data for the vapor-liquid equilibrium of aqueous solutions of a single polyelectrolyte with various counterions. Abbreviations (shown in Table 2) are used to characterize the polyelectrolyte and the experimental procedures (MO membrane osmometry DMO differential membrane osmometry VO vapor pressure osmometry ISO isopiestic experiments EMF electromotive force measurements including also measurements with ion-selective electrodes as well as titration FPD freezing point depression GDM gel deswelling investigations). Table 3 gives a survey for aqueous solutions of poly(styrene sulfonic acid).

ADMET polymers are easily characterized using common analysis techniques, including nuclear magnetic resonance ( H and 13C NMR), infrared (IR) spectra, elemental analysis, gel permeation chromatography (GPC), vapor pressure osmometry (VPO), membrane osmometry (MO), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The preparation of poly(l-octenylene) (10) via the metathesis of 1,9-decadiene (9) is an excellent model polymerization to study ADMET, since the monomer is readily available and the polymer is well known.21 The NMR characterization data (Fig. 8.9) for the hydrogenated versions of poly(l-octenylene) illustrate the clean and selective nature of ADMET. 

The samples prepared by this chlorosilane route are characterized by high degrees of molecular and compositional homogeneities, as was confirmed by the exhaustive characterization data provided by SEC, membrane osmometry, low angle laser light scattering, differential refractometry, vapor pressure osmometry, UV-SEC, and NMR. The most important feature of the method is that every step of the reaction is monitored by taking small aliquots from the reaction mixture. 

M.W. was difficult to obtain because of the Insolubility of the polymer In common organic solvent. M.W. was determined either by vapor pressure or membrane osmometry. bDetermlned by differential scanning calorimetry, cseventy-two hours immersion at room temperature Test for reversion resistance. 

The copolymers were characterized by IR, 13-C and 1-H NMR, viscometry, membrane osmometry (MO), and differential scanning calorimetry (DSC) in order to determine their microstructures, molecular weights and thermal stabilities. 

The membrane osmometry method depends upon finding a suitable membrane which will allow solvent to move through the membrane but not allow motion of the solute in the reverse direction. That is, if a solute and solvent are separated by a semipermiable membrane as shown below in Fig. 4.43, the motion of the solvent will create an increase in pressure in the solute which can be measured by the relative difference of the height of the two fluids in their respective capillaries. This pressure differential can be related to the number average molecular weight. 

Measurements performed to determine the molar masses of polymers yield - as a valuable byproduct - information on the pair interaction between the macromolecules [30]. The composition dependence of the osmotic pressure Tiosm observed via membrane osmometry is directly related to the chemical potential of the solvent [cf. (14) of Sect. 2] and provides the second osmotic virial coefficient A2, from which Xo> Ihe Flory-Huggins interaction parameter in the limit of high dilution becomes accessible [cf. (15)]. Such data are particularly valuable because they can be measured with higher accuracy than the x values for concentrated polymer solutions and because they represent a solid starting point for the sometimes very complex function xiV )- In principle, membrane osmometry can also be operated with polymer solutions of different composition in the two chambers (differential osmometry) to gain data for higher polymer concentrations however, little use is made of this option. 

Measurements became easier with rapidly equilibrating membrane osmometers with servo pressure control. The instrament senses differences in osmotic pressure based on the mass transport through the membrane. The pressure differential between solvent and solution is then controlled by increasing the solution level to hydrostatically counterbalance the osmotic pressure 71. The success of the osmometry... 

Isopiestic [33] experiments also offer access to chemical potentials. This method monitors the conditions under which the vapor pressures above different solutions of nonvolatile solutes (like polymers or salts) in the same solvent become identical, where one of these solutions is a standard for which the thermodynamic data are known. These experiments can be considered to be a special form of differential osmometry (cf. Sect. 3.2) where the semi-permeable membrane, separating two solutions of different composition, consists of the gas phase. 

Solvent activities of polymer solutions with polymer concentrations of up to about 30 wt% can be measured by osmometry (membrane as well as vapor-pressure osmometry), light scattering, ultracentrifuge (of course, all these methods can also be applied for polymer characterization and can be extrapolated to zero polymer concentration to obtain the second virial coefficient), and differential vapor pressure techniques. Ciyoscopy and ebulliometry can also be used to measure solvent activities in dilute and semidilute polymer solutions, but with limited success only. 

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