Vapor pressure osmometry molecular weights measured

However, because of the high price, MALDI-TOF mass spectrometers have not come into wide use. Vapor pressure osmometry (VPO), an old and traditional method for estimating molecular weight, is useful in the field of CPO chemistry. The experimental error of this measurement is approximately 10% however, the obtained data are sufficiently useful to estimate the number of porphyrins in a molecule. 

Molecular weights of the products as measured with vapor pressure osmometry were in good agreement with the calculated ones. Interestingly, resins based on hexahydrophthalic anhydride and diisopropanolamine with tertiary amines as functional groups are soluble in water without quaternization of the... 

Analysis of Defined Fractions. Quantitative infrared analysis was used for those fractional groups that have definitive bands average absorptivities were estimated using model compounds (12, 16, 17). Table I lists the infrared bands and the apparent integrated absorption intensities (B) used. Quantitative IR spectra were measured in methylene chloride with 0.05 cm sodium chloride cells, using a Perkin-Elmer 521 infrared spectrophotometer. Peak area was measured by planimetry. Molecular weights were determined by vapor-pressure osmometry in benzene. 

To confirm the occurrence of the polymorphic transition predicted in the section 4 and to elucidate the mechanism, it is primarily necessary to clarify the enantiomeric assembly mode in the first-formed metastable crystal prior to the polymorphic transition and compare it with the stable crystal structure after the polymorphic transition with respect to a compound showing Preferential Enrichment. Since it is very possible that the stable molecular assembly structure in solution would be retained in the crystalline phase first-formed by crystallization from the same solvent,20 at first, we have investigated the enantiomeric association mode in solutions of the racemates showing Preferential Enrichment. Consequently, in our case, the variable temperature H NMR technique proved to be inapplicable to deciding which molecular association mode is more stable in solution, homochiral or heterochiral.21 Instead, the combined use of the solubility and supersolubility measurements under various conditions and the number-averaged molecular weight measurement by vapor pressure osmometry turned out to become a potent tool for this objective. 

Figure 10. Number-averaged molecular weight measurement of the racemate and nonracemic sample of ST in CHC13 at 30°C by vapor pressure osmometry. (Reprinted with permission from ref 18. Copyright 2003 American Chemical Society.)...

Molecular weight determination of carbosilane dendrimers is best accomplished with electrospray or MALDI-TOF mass spectroscopy, but is also possible with vapor pressure osmometry measurements. In many cases, MALDI-TOF data is sufficiently accurate to indicate slight structural imperfections in dendrimers due to incomplete reactions. Gel permeation chromatography is generally not an effective means of measuring molecular weights of carbosilane dendrimers due to the substantial differences in hydrodynamic volume between spherical dendrimers and linear polystyrene standards. 

Brzezinski J, Glowala H, Kornas-Calka A (1973) Note on the molecular weight dependence of the calibration constant in vapor pressure osmometry Eur Polym J 9 1251-1253 Burge DE (1979) Calibration of vapor pressure osmometers for molecular weights measurements J Appl Polym Sci 24 293-299... 

Hansen, E.H. and Schnitzer, M. Molecular weight measurements of polycarboxylic acids in water by vapor pressure osmometry. Anal Chim. Acta 46, 247-254 (1969). 

Molecular weights were based on polystyrene standards. Vapor pressure osmometry and light-scattering measurements indicate that the true molecular weights are approximately 2 times larger. 

Bruceton coal was depolymerized in refluxing phenol using p-toluenesulfonic acid (HOTs) catalyst (29). The products were 91% extractable into pyridine and had a number average molecular weight of 400 in pyridine, measured by vapor pressure osmometry. Yet most of the materials in this solution have molecular weights above 2500. 

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