Chain-length distribution method

Because the higher alcohols are made by a number of processes and from different raw materials, analytical procedures are designed to yield three kinds of information the carbon chain length distribution, or combining weight, of the alcohols present the purity of the material and the presence of minor impurities and contaminants that would interfere with subsequent use of the product. Analytical methods and characterization of alcohols have been summarized (13). 

It has been shown that equivalent information can be obtained by analysis of logfnumbcr chain length distribution) plots (the log CLD method)."4" 7 For the case where termination is wholly by disproportionation or chain transfer, it is possible to show that (eq. 6) applies ... 

Another chromatographic method is pyrolysis/gas-liquid chromatography. The sample is mixed with P205 and heated to 400°C. This technique yields the chain length distribution of the fatty acids initially used [107],... 

Principle. The content of 1,4-dioxane in ether sulfates is determined by headspace gas chromatography according to the standard additions method. The method is suitable for all ether sulfates and gives reliable results independent of chain length distribution and water content. 

A useful alternate to the Mayo plot for determining Cs (as well as other transfer constants) is the chain length distribution (CLD) method based on the molecular weight distributions obtained from size exclusion chromatography (SEC) [Christie and Gilbert, 1996, 1997 Heuts et al., 1998, 1999 Moad and Moad, 1996]. The limiting slope AHIGH of a... 

A simple alternative method was proposed by Gilbert et al. [296, 297] to determine the chain transfer constants based on the chain length distribution (CLD). If the dominant chain termination mechanism is chain transfer to monomer, the instantaneous numerical MWD (the number fraction distribution) is given by ... 

The main feature of polymers is their MMD, which is well known and understood today. However, several other properties in which the breadth of distribution are important and influence polymer behavior (see Figure 1) include physical, the classical chain-length distribution chemical, two or more comonomers are incorporated in different fractions topological, polymer architecture may differ (e.g., linear, branched, grafted, cyclic, star or comb-like, and dendritic) structural, comonomer placement may be random, block, alternating, and so on and functional, distribution of chain functions (e.g., all chain ends or only some carry specific groups). Other properties the polymers may disperse (tacticity and crystallite dimensions) are not of the same general interest or cannot be characterized by solution methods. 

Abstract This article summarizes recent developments in the synthesis of polypeptides and hybrid peptide copolymers. Traditional methods used to polymerize -amino acid-N-carboxyanhydrides (NCAs) are described, and limitations in the utility of these systems for the preparation of polypeptides are discussed. Recently developed initiators and methods are also discussed that allow polypeptide synthesis with good control over chain length, chain length distribution, and chain-end functionality. The latter feature is particularly useful for the preparation of polypeptide hybrid copolymers. The methods and strategies for the preparation of such hybrid copolymers are described, as well as analysis of the synthetic scope of the different methods. Finally, issues relating to obtaining these highly functional copolymers in pure form are detailed. 

To apply the method of moments, the definitions of the /fth moments of the chain length distributions (CLDs) for live and dead polymer, respectively, are invoked ... 

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