Polystyrene equivalent molecular masses

To apply the universal calibration procedure, it is necessary to make some important assumptions or to carry out extensive preliminary testing with respect to the general applicability of the procedure and on the suitability of 

In fact, SEC is a particularly good technique for simply comparing MMDs of samples and expressing the results as the polystyrene equivalent molecular masses. This avoids the use of possibly questionable assumptions, and emphasizes to the user the comparative nature of the results. It is important to state that there could be considerable differences between the polystyrene equivalent and the actual molecular masses of the samples being considered. 

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Empirical approach. In SEC, a calibration curve of log molecular mass (log M) V. retention volume (Fr) must first be constructed in order to calculate molecular mass averages of the polymers in question. It is usual to report the results as polystyrene equivalent molecular masses, using a calibration curve constructed with polystyrenes of known molecular masses having narrow MMD. For accurate estimation of copolymer molecular weight, one must use a calibration curve for the copolymer in question. Therefore, it is necessary and important to estimate molecular mass of the copolymer species eluted at retention volume i. 

The conductivity behavior of polyelectrolytes does not correspond to either of these low-molecular electrolytes. A considerable amount of experimental work has been carried out with various polyelectrolyte systems. The results of these investigations exhibit a wide diversity of conductivity behavior. Even measurements with the same kind of polyelectrolyte, carried out by different investigators, may differ considerably with regard to the value of equivalent conductivity, as well as to its concentration dependence. The factors that may affect the results are the purity of samples, the molar mass of the polyelectrolyte, and its molecular mass distribution. Polyelectrolytes that have been extensively studied and for which these factors can reasonably be controlled are polystyrene sulphonates (PSS). The acid (HPSS) can easily be prepared from narrow molecular mass polystyrene by sulphonation with concentrated sulphuric acid [25], As it is a strong acid, it... 

The refractometer trace showed a broad peak plus two partially resolved sharp peaks with an overall equivalent carbon number (ECN) range of C13-C96 with a maximum at C43. The equivalent carbon number is that of the n-alkane which elutes at the sample elution volume. In this case, the calibration was extended by the use of low-molecular-mass polystyrenes. The ECN gives a rough measure of molecular size. The two sharp peaks at ECN Cl5 and C19 are seen on the lower molecular mass side of the envelope. No peaks were visible, however, at high elution volumes corresponding to free benzoic, p-coumaric or cinnamic acids. 

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