Vapour phase osmometry

The temperature differences found experimentally are less than expected theoretically because of heat losses within the apparatus. As indicated in the earlier part of this chapter, the experimental approach is to measure these temperature differences at a number of different concentrations and extrapolate to c = 0. The apparatus is calibrated using standard solutes of low relative molar mass, but despite this, the technique can be used on polymers up to of about 40 000. 

The technique is useful in that only small amounts of the sample polymer are needed, though experimentally it is time-consuming and may require great patience in use. This is because the technique does not measure equilibrium vapour-pressure lowering, but measures vapour-pressure lowering in a steady-state situation. Thus care must be taken to ensure that time of measurement and droplet size are standardised for both calibration and sample measurement. 

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In which the ratio m/n is close to 3. The silane was produced by free radical copolymerization of vinyltriethoxysilane with N-vinylpyrrolidone. Its number-average molecular weight evaluated by vapour-phase osmometry was 3500. Porous silica microballs with a mean pore diameter of 225 A, a specific surface area (Ssp) of 130 m2/g and a pore volume of 0.8 cm3/g were modified by the silane dissolved in dry toluene. After washings and drying, 0.55% by weight of nitrogen and 4.65% of carbon remained on the microballs. Chromatographic tests carried out with a series of proteins have proved the size-exclusion mechanism of their separation. 

Average of cryoscopy, ebulliometry, 11,000 15,300 18,500 and vapour-phase osmometry Rapid membrane osmometer, first 19,900 22,100 27,900 observable values (5-7 min after sample introduction)... 

Vapour phase osmometry is found satiable for determining Mn of low Molecular weight samples. This... 

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... 

Membrane osmometry Vapour phase osmometry End group analysis... 

In the field of self-assembly of molecular components to generate defined structures which can be used as molecular devices, structural and functional information must be contained at the molecular level. The approach described in 1993 in Lehn s group was to use two complementary components a mesa 5,15-diuracil-substituted porphyrin and an alkyl triaminopyrimidine.- The interaction between the hydrogen-bonded sites of both components led in large part to a bis-porphyrin supramolecular cage structure 6 as evidenced by proton NMR and fluorescence and electrospray mass spectroscopy as well as by vapour phase osmometry (Figure 7). 

Apart from these techniques, conversion of the insoluble poly(p-phenylene) to a soluble derivative has been used. Friedel-Crafts alkylation of PPP, prepared by the Kovacic route, yields a soluble product which upon analysis by GPC and vapour-phase osmometry gives a DP of 15 [182]. The same material has also been hydrogenated by means of a rhodium catalyst at high temperature and pressure. The corresponding soluble cyclohexane has an average number of cyclohexane units per chain of 8 with a maximum of 16 and a minimum of 4 [183]. 

Examination of the of the cyclic product from the polymerization in the presence of 15-crown-5, after short path very high vacuum distillation, showed that it was mostly (90%) a cyclotetrasilane. It shows a MW of 512 by mass spectmm, and the corresponding cyclic material prepared from propylmethyldichlorosilane, a molecular weight of 344. The latter material also gave a molecular weight of 355 ( 15) by vapour phase osmometry. 

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