Cloud-point titration

The adsorption of block and random copolymers of styrene and methyl methacrylate on to silica from their solutions in carbon tetrachloride/n-heptane, and the resulting dispersion stability, has been investigated. Theta-conditions for the homopolymers and analogous critical non-solvent volume fractions for random copolymers were determined by cloud-point titration. The adsorption of block copolymers varied steadily with the non-solvent content, whilst that of the random copolymers became progressively more dependent on solvent quality only as theta-conditions and phase separation were approached. 

The theta (0) conditions for the homopolymers and the random copolymers were determined in binary mixtures of CCl and CyHw at 25°. The cloud-point titration technique of Elias (5) as moaified by Cornet and van Ballegooijen (6) was employed. The volume fraction of non-solvent at the cloud-point was plotted against the polymer concentration on a semilogarithmic basis and extrapolation to C2 = 1 made by least squares analysis of the straight line plot. Use of concentration rather than polymer volume fraction, as is required theoretically (6, 7 ), produces little error of the extrapolated value since the polymers have densities close to unity. 

Several methods can be used to determine theta solvents. These include phase equilibria studies (see Phase Equilibria in Poor Solvents), determination of second virial coeflJicient (see Problem 3.8), viscosity-molecular weight relationship, and cloud point titration. 

In the cloud point titration method, polymer solutions of different concentrations are titrated with a nonsolvent until the first sign of cloudiness (see Phase Equilibria in Poor Solvents). The logarithm of the nonsolvent concentration at the cloud point is then plotted against the logarithm of the polymer concentration at the cloud point and extrapolated to 100% polymer. The solvent/non-solvent mixture corresponding to the 100% polymer is a theta-mixture. 

The miscibility limits for the furfural-water binary are at A and B. The miscibility boundary (saturation curve) AEPRB is obtained experimentally by a cloud-point titration water, for example, is added to a (clear) 50 wt% solution of furfural and glycol, and it is noted that the onset of cloudiness due to the formation of a second phase occurs when the mixture is 10% water, 45% furfural, 45% glycol by weight. Further miscibility data are given in Table 3.2. 

CP = cloud point titration PE = phase equilibria VM = intrinsic viscosity/molar mass A = virial coefficient... 

The cloud-point titration method (Section 6.6.5) can also be applied to copolymers whose monomeric units are chemically not very different. In this method, solutions of various concentrations are titrated with nonsolvent to the first cloud point. By extrapolation to 100% polymer, a critical volume fraction 3 of the nonsolvent is obtained, which normally depends linearly on the copolymer composition. 

Glass transition and Sometimes No Sometimes calibration via cloud point titrations... 

Other methods used for stereoregularity determinations involve the use of dipole moments, streaming birefringence, rate of saponification, and cloud-point titration. However, all these methods are only applicable to special polymers and/or are only indirect methods, and so they have not found general application. 

The process uses very dilute solutions, normally in the concentration range of 2 between 10" and 10. In what is called the cloud-point titration method, dilute polymer solutions are titrated with nonsolvent at constant temperature to the first cloud point. The volume fraction 3 of nonsolvent to give the first cloud point is plotted against the logarithm of the volume fraction 2 of the polymer at the cloud point. The extrapolated straight line obtained for a hoinologous series at a point on the 2 = 1 axis was found experimentally and theoretically to be equivalent to (3)0 (Figure 6-19). (3)e corresponds to the solvent-precipitant theta mixture for the polymer at this temperature. 

The molar mass distribution can, at least in principle, be determined by the cloud-point titration or turbidimetric titration method. In turbidimetric titration, a precipitant is added continually, with stirring, to a very dilute 0.01%) solution, and the increase in turbidity is observed as a function of the quantity of precipitant added. The turbidity curve which is obtained is a qualitative measure of the molar mass distribution. These curves are difficult to evaluate quantitatively, however, since the turbidity continually changes because of the coagulation of the droplets during titration. The turbidity is therefore not entirely due to the molar mass and concentration of the polymer. 

The determination of the theta temperature by several techniques, such as intrinsic viscosity, phase equilibria, osmometry, light scattering, sedimentation equilibrium, and cloud point titration has been discussed comprehensively in a number of sources [1,14—16]. The influence of... 

The first attempts to use interactive stationary phases for the separation of polyolefins started in 2003. Macko et al. used an isocratic separation system for PE-PP blends [136,137]. For the separation of the two polymers, TCB was used as a thermodynamically good solvent for both components and ethylene glycol monobutylether (EGMBE) as eluent. Dimethylsiloxane-modified silica gel was used as stationary phase. As a result, PE eluted almost irrespective of its molar mass under limiting conditions, while PP eluted in the SEC mode before the PE components. Resolution of this method, however, was rather poor and additionally limited by the poor solubility of the polyolefins. These results triggered some in-depth studies on the solubility of polyolefins in different solvents using cloud point titration [138] and the testing of zeolites as selective stationary phases [139-142]. 

To characterize the obtained biphasic systems, the phase diagrams determined by the cloud-point titration are usually constructed. The binodal has been described by an empirical model developed by Merchuk and coworkers (Merchuk et al., 1998). The mathematical representation of the curves fitted the best to experimental data was the following ... 

Cloud Temperature Titration (CT) In a variation of the cloud point titration method, cloud temperatures may be determined by cooling or heating of dilute polymer... 

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