Polymers vapour pressure osmometry

Chain Length Properties of the Modified Polymers. A number of partially hydrogenated and hydroxymethyl ated polybutadienes were analyzed using vapour pressure osmometry, dilute solution viscometry and gel permeation chromatography. The parent polybutadiene had Mn in the range of 9,000 to 50,000. In the case of vapour pressure osmometry, the data were reproducible for polymers with Mn less than 20,000. All the polymers obtained (hydrogenated and... 

The intrinsic viscosities and Mn (from vapour pressure osmometry) of a number of chemically modified polymers are listed in Table I. Figure 11 shows a plot of intrinsic viscosity versus... 

Vapour pressure osmometry is the second experimental technique based on colligative properties with importance for molar mass determination. The vapour pressure of the solvent above a (polymer) solution is determined by the requirement that the chemical potential of the solvent in the vapour and in the liquid phase must be identical. For ideal solutions the change of the vapour pressure p of the solvent due to the presence of the solute with molar volume V/1 is given by... 

Experimental considerations Sample preparation and data evaluation are similar to membrane osmometry. Since there is no lower cut-off as in membrane osmometry, the method is very sensitive to low molar mass impurities like residual solvent and monomers. As a consequence, the method is more suitable for oligomers and short polymers with molar masses up to (M)n 50kg/mol. Today, vapour pressure osmometry faces strong competition from mass spectrometry techniques such as matrix-assisted laser desorption ionisation mass spectrometry (MALDI-MS) [20,21]. Nevertheless, vapour pressure osmometry still has advantages in cases where fragmentation issues or molar mass-dependent desorption and ionization probabilities come into play. 

UV spectroscopy shows that quaternary phosphonium ions are present but, of course, does not prove that they are joined to polymer chains. The authors fractionated their polymers with a THF/water solvent-non solvent combination. They had found that the model compound described above could be quantitatively separated from phosphorus free poly(methylenemalonie ester). After fractionation the phosphorus content fell, but when the molecular weight was determined by vapour pressure osmometry, it was found that there was approximately one phosphonium group per chain. The absorption coefficient of the model compound was used to calculate the phosphorus content of the product. 

Direct evidence for the adsorption of both enantiomorphs of 7-benzyl-glutamate NCA on to the L-polymer in dioxan was obtained by Williams et al. [62] using vapour pressure osmometry to monitor the free-monomer concentration. The results are shown in Table 3. It is of interest that the D-monomer is adsorbed preferentially by an L-polymer (Kld/Kll 1-4). The authors do not state that the amine end-group of the polymer was deactivated in this work if not, complications which might eirise from in situ polymerization appear to have been disregarded. 

Hunt, B. J. James, M. I. (1999) Vapour pressure osmometry/ membrane osmometry/ viscometiy, in Pethrick, R. A. Dawkins, J. V. (Eds.) Modern Techniques for Polymer Characterisation, Chichester John Wiley and Sons. 

The technique described as vapour pressure osmometry is really nothing to do with proper osmometry. The basis of the method depends on the fact that there is a vapour pressure difference between a polymer solution and the pure solvent, i.e. there is a difference in the chemical potential of the solvent in the solution and the pure state. Two matched thermistors are placed in a thermostatted environment which is saturated with the vapour of the solvent used to dissolve the polymer (see Figure 2.19). The thermistors are connected... 

The value of vapour pressure osmometry is that the technique is particularly good for low molecular weight polymers, i.e. for molecular weights less than approximately 20000. Membrane osmometry is subject to error at low molecular weight because of solute diffusion through membranes, which are not perfectly semi-permeable as required by the theory. This makes vapour pressure osmometry a convenient method for obtaining M for low molecular weight polymers. 

The polyacrylate (6) with a pendant dimeric carbazole unit, l,2-trans-bis(9H-carbazol-9-yl)cyclobutane (DCZB), does not show excimer fluorescence and exhibits improved hole drift mobility [52]. It is obtained by free-radical polymerization of the corresponding acrylate [53], The molecular weight of the polymer (6) established by vapour pressure osmometry is 46,000. The hole drift mobility of polymer (6) is more than ten times higher than that of PVK or poly(9-ethyl-3-vinylcarbazole). 

Molar masses of the samples were determined by field-desorption mass spectrometry (FD-MS), vapour pressure osmometry (VPO), and GPC. GPC was calibrated with PVFc. Both, calibration via an oligomer sample in which oligomers from = 3 through n = 11 could be identified and via polymers produced by living anionic polymerization (characterized by VPO or FD-MS), gave similar results and excellent agreement with theoretical values. 

An alternative to membrane osmometry is vapour pressure osmometry, in which the lowering of solvent vapour pressure due to polymer solute is exploited. If one drop of pure solvent and one of solution are placed close together, solvent from the vapour will condense on the solution drop because of the vapour pressure difference. This causes the temperature of the solution drop to rise, which can be measured with a sensitive thermometer. Vapour pressure osmometry is useful for low molar mass polymers where membrane osmometry cannot be used because the polymer molecules are small enough to be able to pass through the membrane. 

Vapour pressure osmometry involves the indirect measuring of the lowering of the vapour pressure of a solvent due to the presence of a solute. It is based on the measurement of the temperature difference between droplets of pure solvent and of polymer solution maintained in an isothermal atmosphere saturated with the solvent vapour. Calibration is by the analysis of standards of known molecular weight and should be over the entire range of molecular weights of interest to ensure the best results. The technique is useful for polymers that have molecular weights in the 500-50,000 range. 

The experimental measurement of these averages has largely been performed on polymers in solution (Hunt and James, 1999). Since M depends on the measurement of the number of polymer chains present in a given mass, colligative properties such as vapour-pressure depression AP (measured by vapour-phase osmometry) and osmotic pressure (measured by membrane osmometry) relative to the pure solvent, can in principle provide the molar mass through an equation of the form... 

Vapour pressure depression and membrane osmometry are the most common methods to determine the polyer-solvent interaction parameter. The latter method will be described briefly. In a membrane osmometer a dilute polymer solution has been separated from pure solvent by means of a membrane. The membrane is penneable for solvent molecules but not for polymer molecules. Due to a chemical potential difference solvent molecules will diffuse from the diluted phase to the concentrated phase and this results in a pressure increase which is called the osmotic pressure ti (see also section VI - 2 for a more detaUed description of osmosis). The osmotic pressure is given by... 

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