Polyethylene Mark-Houwink constants

The original Mark-Houwink constants for polyethylene in ODCB were measured at 135°C by Pollock and Kratz (16), by comparing the intrinsic... 

Kirkland and co-workers have used this technique to determine the MWD of water-soluble polymers including polyethylene oxide in the 10 -2 x 10 molecular weight range, including sodium PS sulfates and dextrans [238]. Also, they applied the techniques using Mark-Houwink constants to PS, polyisoprene, poly-a-methylstyrene, polyacrylates, polyvinyl pyrrolidone, and PVC [238]. 

Ki, a2 = Mark-Houwink constants for polyethylene Ml = molecular weight of polystyrene M2 = molecular weight of polyethylene... 

Universal Calibration In the conventional calibration (described above), there is a problem when a sample that is chemically different from the standards used to calibrate the column is analyzed. However, this is a common situation for instance, a polyethylene sample is run by GPC while the calibration curve is constructed with polystyrene standards. In this case, the MW obtained with the conventional calibration is a MW related to polystyrene, not to polyethylene. On the other hand, it is very expensive to constmct calibration curves of every polymer that is analyzed by GPC. In order to solve this problem, a universal calibration technique, based on the concept of hydrodynamic volume, is used. As mentioned before, the basic principle behind GPC/SEC is that macromolecules are separated on the basis of their hydrodynamic radius or volume. Therefore, in the universal calibration a relationship is made between the hydrodynamic volume and the retention (or, more properly, elution volume) volume, instead of the relationship between MW and elution volume used in the conventional calibration. The universal calibration theory assumes that two different macromolecules will have the same elution volume if they have the same hydrodynamic volume when they are in the same solvent and at the same temperature. Using this principle and the constants K and a from the Mark-Houwink-Sakurada equation (Eq. 17.18), it is possible to obtain the absolute MW of an unknown polymer. The universal calibration principle works well with linear polymers however, it is not applicable to branched polymers. 

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