Size exclusion chromatography branching measurement

A viscosity online detector in a size exclusion chromatography (SEC) instrument allows for a universal calibration for polymers with known K- and a-values. For polymers that are only soluble at high temperature, e.g., polyolefines, high-temperature detectors are available, which can be operated up to 200°C. In addition to molar mass measurements, viscosity detectors have also been employed successfully to obtain structural information of branched polymers [28]. 

The experimental techniques for the study of conformational branched properties in solution are the same as used for linear chains. These are, in particular, static and dynamic light scattering, small angle X-ray (SAXS) and small angle neutron (SANS) scattering methods, and common capillary viscometry. These methods are supported by osmotic pressure measurements and, nowadays extensively applied, size exclusion chromatography (SEC) in on-line combination with several detectors. These measurements result in a list of molecular parameters which are given in Table 1. 

The calibration standards included sodium form polystyrene sulfonates obtained from Pressure Chemical Co., Pittsburgh, Pa., and sodium toluene sulfonate. Measurements were taken at 0.5 to I.Oml/mln flow rates. The logarithm of the molecular weight of the standards was linear it suggests a framework for approaching an interpretion of the structure of the scission products. This application of size exclusion chromatography measurements must be viewed as a first approximation because of the unmeasured differences between the chromatographic behavior of the linear standards and the expected branched structure of the scission products. 

These dendrimers have branch cell segments which are approximately one-half the dimensions of the PAMAM series (5 A versus 10 A) and possess chemical linkages which have much greater chemical and physical stability. A comparison of theoretical molar masses, number of terminal groups, CPK predicted diameters, and measured diameters (size exclusion chromatography, SEC) as a function of generation is shown in Table 3. 

One dilute solution property of practice interest is exclusion chromatography, widely used for characterization of molecular wei t and its distribution. It is generally assumed that separation is governed by the size of the polymer molecule, the smaller molecules eluting later. Branched polymers are in fact retained on the column longer than their linear counterparts of the same molecular weight. Benoit and coworkers have suggested empirically that the elution volume is a unique function of the hydrodynamic volume as measured by the product Confirmation of... 

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