engleski

Analysis of Polymer Molecular Weight Distribution Data Obtained by the Size Exclusion Chromatography Method

The averages of polymer molecular weight distribution (MWD) and the polydispersity index are usually obtained by the size exclusion chromatography (SEC) method. The polydispersity index as a measure of the width of molecular weight distributions (MWD) is theoretically very important. However, it is commonly misinterpreted as a single and unique measure of MWD width. In this work, the origin and solutions of the polydispersity index problem are clearly described via several theoretical distribution functions, i.e., those which are most widely applied for the description of polymer MWDs. The conclusions are confirmed by the analysis of MWDs of real samples, namely styrene-acrylonitrile copolymers. In addition, a complete procedure for the MWD data analysis is presented. The procedure is composed of three different normalization methods. If theoretical distribution functions are to be fitted to the experimental MWD data, the normalization method 1 has to be applied previously. After the choice of the best theoretical function is made, the normalization method 2 is performed to enable comparison of several MWD data sets with respect to the MWD width. For the comparison of MWD shapes, disregarding the distribution width, the normalization method 3 is developed. Such a complex procedure is essential for the correct interpretation and comparison of different molecular weight distributions of polymers. However, the application of the procedure is not limited to the field of polymers, since other distributions may be analyzed as well, e.g., particle size distribution, residence time distribution, etc.

nije evidentirano

nije evidentirano