Colligative Property Measurement

Table 98) correlated with the Hammett acidity function H0 rather than with log [ROH]/[R+]377. However, subsequent spectroscopic analysis and colligative property measurements showed that anils are present in strong sulphuric acid entirely as the monoprotonated species and since reaction is not instantaneous, it must be occurring on some other species, assumed to be diprotonated. For this to be true a plot of log rate versus the acidity function H+ would have to be linear the values of H+ were not known in this medium but were considered to parallel... 

Colligative properties measure average relative molar masses, M, and in the case of osmotic pressure, II, the important relationship is ... 

Theta temperature (Flory temperature or ideal temperature) is the temperature at which, for a given polymer-solvent pair, the polymer exists in its unperturbed dimensions. The theta temperature, , can be determined by colligative property measurements, by determining the second virial coefficient. At theta temperature the second virial coefficient becomes zero. More rapid methods use turbidity and cloud point temperature measurements. In this method, the linearity of the reciprocal cloud point temperature (l/Tcp) against the logarithm of the polymer volume fraction (( )) is observed. Extrapolation to log ( ) = 0 gives the reciprocal theta temperature (Guner and Kara 1998). 

Molecular weight Determination by Colligative Property Measurements... 

The most dramatic effects of Lewis bases in organolithium chemistry are observed in polymerization reactions. Aside from colligative property measurements, there is little direct quantitative information on the nature of the organolithium-base interactions responsible for the observed effects. The calorimetric method has been used also to examine the fundamental nature of the interaction of bases with polymeric organolithium compounds 83,88,89). Information is now available on the ground-state interaction of bases with poly(styryl)lithium (PSLi), poly(isoprenyl)lithium (PILi) and poly(butadienyl)lithium (PBDLi). 

Traditional methods for measuring molecular weight date from the dawn of modem physical chemistry in the 19th century. These relied on so-called colligative property measurements (see box opposite), such as boiling point elevation and freezing... 

End-group analysis is not a colligative property measurement in the strict sense of the concept. It can be used to determine M of polymer samples if the substance contains detectable end groups, and the number of such end groups per molecule is known beforehand. (Recall that a branched molecule can have many ends.)... 

Aiken G. R. and Gillam A. H. (1989) Determination of molecular weights of humic substances by colligative property measurements. In Humic Substances II In Search of Structure, (eds. M. H. B. Hayes, P. MacCarthy, R. L. Malcolm, and R. S. Swift) Wiley, Chichester, pp. 515-544. 

Glover C. A. (1975) Absolute colligative property measurements. In Polymer Molecular Weights (ed. P. E. Slade, Jr.) Dekker, New York, pp. 79-159. 

Number-average data of a polydisperse system are of little value. It is important to use other methods, such as small-angle X-ray scattering, to determine the extent of polydispersity of the system before making conclusions from colligative-property measurements. 

Colligative property measurements imply that R2Mg compounds are monomeric up to high concentrations in the... 

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