Critical viscosity molecular weight

Since pc 1/2, we observe that Me 2Mg, as commonly observed. Mg is determined from the onset of the rubbery plateau by dynamic mechanical spectroscopy and Me is determined at the onset of the highly entangled zero-shear viscosity law, T) M. This provides a new interpretation of the critical entanglement molecular weight Mg, as the molecular weight at which entanglement percolation occurs while the dynamics changes from Rouse to reptation. It also represents the... 

The concept of chain entanglements influencing the line-widths, or T2 s, can be examined more directly by studying the influence of molecular weight. It is well established that the zero shear bulk viscosity of all amorphous polymers is directly proportional to the molecular weight below a critical low molecular weight, M., and above this molecular weight increases as the 3.5 power of M. ( ) ( ) (50) M, represents approximately... 

It is important to note that there is a critical threshold molecular weight below which there is little if any entanglement of polymer chains. Melt viscosity is a measure of the tendency (speed) of melted materials to flow. 

Today, there is more emphasis on quality of excipients. For example, some inherent quality variability may occur in the natural products magnesium stearate and sodium starch glycolate. What is the impact of the variability of these excipients on product quality attributes Also, excipient viscosity, molecular weight, and particle size relative to API particle size could be critical factors to some formulations. An optimal dissolution method can only be developed on the basis of knowledge of the dmg product. 

Other averages for boiling points are used in evaluating K and the other physical properties in this Appendix. (Refer to Danbert or Maxwell S for details.) This factor has been related to many of the other simple tests and properties of petroleum fractions, such as viscosity, molecular weight, critical temperature, and percentage of hydrogen, so that it is quite easy to estimate the factor for any particular sample. Furthermore, tables of the UOP characterization factor are available for a wide variety of common types of petroleum fractions as shown in Table K.l for typical liquids. 

The development ofand new trends in the determination of molecular weights and molecular weight distribution of aliphatic unsubstituted linear polyamides (nylons) are reviewed here. Critically discussed are intrinsic viscosity - molecular weight relationships and the conformational regidity of nylon chains. Attention is also given to some peculiarities in the behavior of nylons in multicomponent solvents. 

Normal boiling point K Standard specific gravity Molecular weight kg/lunol Liquid viscosity at 100°F mm /s Liquid viscosity at 2iO F mm /s Critical temperature K Critical pressure bar... 

Once the value of the constant and the a value in Eq. (2.36) have been evaluated for a particular system, viscosity measurements constitute a relatively easy method for determining the molecular weight of a polymer. Criticize or defend the following proposition Since viscosity is so highly dependent on molecular weight for M > M, a 10% error in 17 will result in a 34% error in M above M, but only a 10% error in M below M, . 

Among the complications that can interfere with this conclusion is the possibility that the polymer becomes insoluble beyond a critical molecular weight or that the low molecular weight by-product molecules accumulate as the viscosity of the mixture increases and thereby shift some equilibrium to favor reactants. Note that we do not express reservations about the effect of increasing viscosity on the mobility of the polymer molecules themselves. Apparently it is not the migration of the center of mass of the molecule as a whole that determines the reactivity but, rather, the mobility of the chain ends which carry the reactive groups. 

For prediction of the vapor viscosity of pure hydrocarbons at low pressure (below Tr of 0., the method of Stiel and Thodos is the most accurate. Only the molecular weight, the critical temperature, and the critical pressure are required. Equation (2-97) with values of N from Eqs. (2-98) and (2-99) is used. 

If critical pressure and critical temperature are given in Pa and K, respectively, viscosities in centipoise result. The variable Io is either the low pressure pure component or mixture viscosity according to whether a pure component or mixture is being considered. For mixtures, simple molar average pseiidocritical temperature (Kay s rule), pressure, and density, and molar average molecular weight are used. The vapor density can be predicted by the methods previously discussed. Errors of above 5 percent are common for hydrocarbons and their mixtures. Experimental densities will reduce the errors slightly. 

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