Fractionation and molecular weight

Flow field - flow fractionation has been used to fractionate polystyrene and Kirkland and Rementer used thermal field flow fractionation using Mark Houweq constants to determine the molecular weight distribution of polystyrene and poly methylstyrene. 

Desorption chemical ionization mass spectrometry has been used to determine the molecular weight distribution of polystyrene.. The liquid chromatographic behaviour has been studied of polystyrene homopolymers on a C4 pore diameter reversed phase column. Separation was achieved on a molecular weight basis using a tetrahydrofuran- 

Hancock and Synovec have carried out rapid characterization of linear and star branched polystyrene by gradient detection using methylene dichloride solutions of the polymers. This technique measures weight average molecular weights and is more specific than results obtained using a refractive index detector. 

Time of flight secondary ion mass spectrometry has been used to determine the molecular weight distribution of polystyrene.  

didecyl phthalate on diatomaceous earth. O, silicon grease on diatomaceous earth. 

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The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

Notice the similarity in form of Eq. (4.65) with Eq. (4.7), which used the packing fraction to estimate the viscosity. In this case, however, the dependences are the inverse of packing fraction and molecular weight to those in Eq. (4.7). In other words, whatever factors that change viscosity will have the opposite effect on diffusion. As viscosity goes up, diffusivity goes down the inverse is true as well. This relationship is stated... 

Fractionating and Molecular Weight Determination. Another approach to obtain more information on the nature of the responsible... 

Here x, and Mi are the mole fraction and molecular weight of species i in the gas mixture of n species and /x, is the viscosity of pure species i at the system temperature and pressure. 

Because ASPEN is to be used with coal conversion processes, its streams can be designated to carry an arbitrary number of solids or solid phases. This is done by specifying any number of substreams. In fact, the conventional vapor/liquid stream is normally assumed as a substream and solids can comprise other substreams. For the conventional vapor/liquid substream, process data is carried on component molar flows, total molar flow, temperature pressure, specific enthalpy, specific entropy, density, molar vapor fraction, molar liquid fraction, and molecular weight. For solid substreams, which are called "non-conventional substreams," the characterizing data is not as deterministic. The information associated with these substreams is called "attributes". Such attributes may be particle size distribution, ultimate and proximate analyses, or other material specific information. Another type of substream is an "informa-... 

Calculated from mole fractions and molecular weights of SRC-II-Acid (M — 210) and Et3N (M = 101) assuming no complex formation. 

Fig. 8. Equilibrium morphologies attainable in di-block copolymers as a function of weight fraction and molecular weight of species...

An insoluble rhodium catalyst [(nbd)Rh(acac)] has been used to synthesize polyphenylacetylene in the presence of liquid and SCCO2 (82). The catalyst is solubilized in the reaction mixture by addition of a perfluoroalkyl-substituted triph-enylphosphine ligand. Polyphenylactylene formed in good yields (60-75%) had a molecular weight of about 4 x 10 g/mol for THF soluble fractions, and molecular weight distributions in the range of 8-10. 

P(MOBH(14)-TBMA) and P(MOBH-tBOSt), when irradiated (50 mJ/cm ) at room temperature (see Table I ). The photoinduced insolubilization of the polymers increased with MOBH unit fraction and molecular weight. No significant insolubilization was observed for P(MOBH(14)-TBMA) and P(MOBH-tBOSt) because of low fractions of MOBH units (14 -15 mol%). The insoluble fraction of the present polymers was increased by the postexposure-baking (PEB) treatment at relatively lower temperatures (60-120 C). Although, after the irradiation (50 mJ/cm ) at room temperature, the insoluble fractions for P(MOBH(14)-TBMA) and P(MOBH-tBOSt) were negligibly low, the insoluble fraction became 60 and 40%, respectively, after PEB treatment at 90 C for 30 min. No insolubilization was observed when unirradiated polymer films were baked at 90 C for 30 min. 

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