Hyphenation in Polymer Analysis

Polymers are typically complex mixtures in which the composition depends on polymerization kinetics and mechanism and process conditions. To obtain polymeric materials of desired characteristics, polymer processing must be carefully controlled and monitored. Furthermore, one needs to understand the influence of molecular parameters on polymer properties and end-use performance. Molar mass distribution and average chemical composition may no longer provide sufficient information for process and quality control nor define structure-property relationships. Modern characterization methods now require multidimensional analytical approaches rather then average properties of the whole sample [1]. 

Different from low molar mass organic samples, where single molecules are to be determined, for complex synthetic polymers the analytical task is the determination of a distributed property. The molecular heterogeneity of a certain complex polymer can be presented either in a three-dimensional diagram or a 

Using appropriate analytical methods, the type and concentration of the different functionality fractions must be determined and, within each functionality, the molar mass distribution has to be obtained. To do this, two different methods must be combined, each of which is preferably selective towards one type of heterogeneity. For example, a chromatographic method separating solely with respect to functionality could be combined with a molar-mass-selective method. Another approach would be the separation of the sample into different molar mass fractions which are then analyzed with respect to functionality. 

For copolymers, in particular random copolymers, instead of discrete functionality fractions a continuous drift in composition is present (see Fig. 3). To determine this chemical composition drift in interrelation with the molar mass distribution, a number of classical methods have been used, including precipitation, partition, and cross-fractionation [2]. The aim of these very laborious techniques is to obtain fractions of narrow composition and/or molar mass distribution which are then analyzed by spectroscopy and SEC. 

Schematic separation protocol for the analysis of a complex polymer mixture 

---