Index of polydispersity

Thus, the index of polydispersity M /M becomes 1 + p, as shown below ... 

Thus, when p = I, the index of polydispersibility for the most probable distribution for stepwise polymerizations is 2. 

Even with some high yield catalytic systems, the index of polydispersity was inversely proportional to the hydrogen concentration. ... 

For the crystalline polymer obtained with a-TiClj—Al(C2Hj)2Cl at Ti/Al ratio 1, a slight decrease in the index of polydispersity was found between 0 and 3000 minutes. This has been ascribed both to possible diffusion phenomena, even for low conversions, and to the kinetic behaviour of two different types of active centres. 

Areas of application of reaction calorimetry include determination of calorimetric data for reactions and process design, for the kinetic characterization of chemical reactions and of physical changes, for on-line monitoring of heat release and other analytical parameters needed in subsequent process development as well as for the development and optimization of chemical processes with the objective, for instance, to increase yield or profitability, control the morphology or degree of polymerization and/or index of polydispersity, etc. 

The initial structure of die globular or bicontinuous microemulsion is not preserved during polymerization the final system consists in both cases of a dispersion of spherical latex particles with a fairly low index of polydispersity 1.15), as seen from QELS and TEM experiments [48,53,61]. Several factors are responsible for this structural change ... 

The index of polydispersity d can be used to characterize the width of molecular weight distributions, which is defined by... 

Size exclusion chromatography coupled with HPLC (SEC-HPLC or HPSEC) permits not only the determination of the molecular weight, hut also its statistical distrihution, hence the index of polydispersity [49]. Separation of the polymCT species takes place according to their molecular size, or more strictly, their hydrod5mamic volume. This method is claimed to he rapid, reproducible and simple compared with light scattering, osmometry or ultracentrifugation. 

The simplest form of postcorrelation analysis is called the method of cumulants and provides for a mean particle size together with an index of polydispersity. If a defined a priori form of a distribution (as recommended in ISO 13321) is now assumed, the cumulants result can now be expressed as a mean size Xpcs and standard deviation of a size distribution. 

The molecular weights of the hemicelluloses and their carboxymethylated derivatives were determined by GPC on a PL aquagel-OH50 column (3007.7 mm. Polymer Laboratories Ltd.). Detection was achieved with a Knauer differential refractometer. The weight of carboxymethylated hemicelluloses became lower than that of native hemicelluloses (26800 g.moP), as the Mw range from 12213 to 15312 g/mol. In addition, carboxymethyl hemicelluloses had a relatively low index of polydispersity (2.75-2.87), which indicated that the molecular weights of hemicellulosic derivatives were more uniform [72]. 

If k R )j is larger than 4 and if the index of polydispersity is high (M /M > 2), then the extrapolated value of cl at k = 0 gives a molecular weight average between M and Mn- The slope also provides an intermediate value of the average squared radius ... 

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