Vapour pressure osmometry

GPC/SEC, MALDI-MS, membrane osmometry, vapour pressure osmometry, viscometry, light scattering, TDFRS, SAXS, SANS, SEC-HPLC, SEC-MS, SEC-IR, FFF, ultracentrifugation, MALDI-TOF-MS, NMR, capillary electrophoresis... 

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... 

Molecular weights were determined by vapour pressure osmometry in benzene solution using a Knauer apparatus. 5 concentrations over the range 1 - 5 g/ were employed and the molecular weight was obtained by extrapolation to infinite dilution. 

Using Rotating Autoclave Determined by vapour pressure osmometry... 

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. 

Methods for the determination of Molecular weight based on colligative property are vapour-pressure lowering, boiling point elevation (ebulliometry), freezing-point depression (cryoscopy), and the Osmotic pressure (osmometry). 

Analytical procedures The molecular weights of the polyisobutylenes (Systematic name poly(l,l-dimethylethylene) and of the polynorbornadienes (Systematic name poly(3,5-tricyclo[2.2.1.02, b]heptylene) were determined by membrane osmometry in toluene solution and those of the polystyrenes were determined by vapour-pressure osmometry in chloroform. 

The use of our equations will be illustrated by applying them to a few systems from the literature showing simple kinetic behaviour. However, before starting the calculations we must ascertain how reliable the literature data are. There seems little reason to doubt the soundness of the rate data, but almost all the DP data, essential for the calculation of [Pn ], are suspect because in most researches the DP is obtained by GP chromatography (GPC) with a polystyrene (PSt) calibration. The extent of the uncertainty is revealed by two sets of measurements Cho and McGrath [19] found that for poly(nBVE)(PnBVE) the DP determined by vapour pressure osmometry (VPO), which one would favour as closest to the real DPn, is related to that found by GPC, DP(PSt), as... 

Vapour pressure osmometry Requires very small sample size Several concentrations necessary restricted to mol. wt. < ca. 2 x 104 calibration constant must be established with solute of known mol. wt. 1-2... 

Solid state investigations have been generally corroborated by solution studies. The X-ray structure of lithium N-methyl pscudoephedrates102 indicates the tetrameric aggregation in which the lithium atoms are chelated between oxygen and nitrogen (Figure 6). The structure in solution has been demonstrated to be tetrameric in benzene by means of vapour pressure osmometry (VPO, 37 °C) and cryoscopy (5.5 °C). 

The two methods of elaborating DP s give slightly different results which may indicate specific orientation effects, however the two are within 10% and show an excellent correlation with DP s determined by vapour pressure osmometry and this is shown in Fig. 19. 

M(fod)3, where M = Pr or Eu, have been shown278 to undergo association in carboi tetrachloride solution, doubtless of a similar nature to that observed269 in the case o [Pr2(dpm)6], Vapour pressure osmometry on carefully dried solutions showed association int< dimers and trimers, with association quotients as follows (mol-1) Pr2(fod)6, 140 8 Pr3(fod)9 45 5 Eu2(fod)6, 367 22 Eu3(fod)9, 12 2 all at 37 °C. Controlled addition of traces o water was observed to reduce these values presumably it coordinates and splits th< /8-diketonate bridge. This association in solution is in contrast to the more highly hinderet M(dpm)3 complexes which are monomeric in carbon tetrachloride.279... 

Further important information about these products comes from measurements of their molar masses. Of the available methods, vapour pressure osmometry (VPO) and gel permeation chromatography (GPC) are the most widely used, but, because of its sensitivity to low-molar-mass components, VPO tends to yield results which are too low. In contrast, GPC provides a detailed picture of the molar mass distribution. 

Vapour pressure osmometry - in which the molecular weight measured is that of the dimer. 

The up to now most frequently used techniques as, for example, vapour pressure osmometry (VPO) or freezing point depression (with its limitation regarding the solvent dependent measuring temperature) are based upon the colligative properties of the system the classical absolute light-scattering and ultracentrifugation techniques are only occasionally and approximately applicable with respect to the determination of CMC values. Evaluation of critical micelle concentrations which are based on these latter methods suffer considerably from the insensitivity of these techniques if measurements below the CMC, i.e., below about 10-3 mol dm-3, are carried out. More sensitive methods will be discussed below. 

Both vapour pressure osmometry and depression of the freezing point are the standard techniques probably most frequently used to determine the apparent number average molecular weight of the aggregates. The former method is preferred since the temperature of the sample is easily varied, thus allowing the investigation of the temperature dependence of the aggregate size. The accuracy of the commercially available equipment is rather different, and this has to be carefully considered below... 

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. 

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