Osmometry polymer analysis

Among the techniques employed to estimate the average molecular weight distribution of polymers are end-group analysis, dilute solution viscosity, reduction in vapor pressure, ebuUiometry, cryoscopy, vapor pressure osmometry, fractionation, hplc, phase distribution chromatography, field flow fractionation, and gel-permeation chromatography (gpc). For routine analysis of SBR polymers, gpc is widely accepted. Table 1 lists a number of physical properties of SBR (random) compared to natural mbber, solution polybutadiene, and SB block copolymer. 

ADMET polymers are easily characterized using common analysis techniques, including nuclear magnetic resonance ( H and 13C NMR), infrared (IR) spectra, elemental analysis, gel permeation chromatography (GPC), vapor pressure osmometry (VPO), membrane osmometry (MO), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The preparation of poly(l-octenylene) (10) via the metathesis of 1,9-decadiene (9) is an excellent model polymerization to study ADMET, since the monomer is readily available and the polymer is well known.21 The NMR characterization data (Fig. 8.9) for the hydrogenated versions of poly(l-octenylene) illustrate the clean and selective nature of ADMET. 

We report here the results of our recent studies of poly(alkyl/arylphosphazenes) with particular emphasis on the following areas (1) the overall scope of, and recent improvements in, the condensation polymerization method (2) the characterization of a representative series of these polymers by dilute solution techniques (viscosity, membrane osmometry, light scattering, and size exclusion chromatography), thermal analysis (TGA and DSC), NMR spectroscopy, and X-ray diffraction (3) the preparation and preliminary thermolysis reactions of new, functionalized phosphoranimine monomers and (4) the mechanism of the polymerization reaction. 

Vapor pressure osmometry is slightly less sensitive than membrane osmometry (M < 2 X 10 ) but is not affected by very short chains in the polymer sample which migrate through the semipermeable membrane in the case of membrane osmometry. Therefore, it is in particular valuable for the analysis of oligomeric materials. 

The GPC analysis of block copolymers is handicapped by the difficulty in obtaining a calibration curve. A method has recently been suggested to circumvent this difficulty by using the calibration curves of homopolymers. This method has been extended so that the calibration curves of block copolymers of various compositions can be constructed from the calibration curve of one-component homopolymers and Mark-Houwink parameters. The intrinsic viscosity data on styrene-butadiene and styrene-methyl methacrylate block polymers were used for verification. The average molecular weight determined by this method is in excellent agreement with osmometry data while the molecular weight distribution is considerably narrower than what is implied by the polydispersity index calculated from the GPC curve in the customary manner. 

Son and coworkers also reported the syntheses of hyperbranched poly(carbosilanes) via hydrosilylation. In one report, they prepared a series of AB3 carbosilarylene monomers (5, 6 and 7)173 which polymerized cleanly and rapidly to form soluble hyperbranched polymers in high yields. The polymers, ranging in appearance from sticky solids to oils, were characterized by NMR spectroscopy, thermogravimetric analysis, differential scanning calorimetry and vapor pressure osmometry. The polymers possessed subambient Tg... 

Two other techniques that are also used to measure M are not colligative properties in the strict sense. These are based on end-group analysis and on vapor phase osmometry. Both methods, which are limited to lower molecular weight polymers, are described later in this chapter. Some general details of the various procedures for measuring M directly are reviewed in this section. 

Tivo other techniques are also used to measure Af of relatively low-molecular-weight polymers. These are end-group analysis and vapor phase osmometry. 

The functionality / of low-molecular-weight functionalized prepolymers (e.g., polyether polyols used in the preparation of polyurethanes) is often determined by combining the functional group analysis (which yields the equivalent weight of the polymer. Me) with another suitable method of molecular weight (M ) determination, such as vapor phase osmometry. Note that in this respect the functional groups do not have to be end groups. 

A second important focus of our work is the development of suitable analytical methods for the solid state and in solution. The physical characterization of metallo-supramolecular systems has mainly relied on crystal structure determination. Studies have also been performed on surface layers 40-42). The classical analytical methods (like FAB mass spectrometry) or most polymer methods (like light scattering, vapor pressure osmometry or membrane osmometry) can not be used. In solution, ESI mass spectrometry (43-45) and NMR (27,46) have been succesfully applied. We have explored whether MALDI-TOF mass spectrometry in the solid state (Schubert, U. S. Lehn, J.-M. Weidl, C. H. Spickermann, J. Goix, L. Rader, J. Mullen, K., unpublished data.) and sedimentation equilibrium analysis in the analytical ultracentrifuge for solutions may be employed. Grid-like cobalt coordination arrays ([2 X 2] Co(n)-Grid) were used as model systems in the analytical ultracentrifuge (47). 

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