Characterization of Branched Polymers by Multi-Angle Light Scattering and Related Techniques

Long-chain branching belongs to crucial structural characteristics of synthetic and natural polymers affecting many of their important properties. The knowledge of branching also brings information about the kinetics of polymerization reactions or side reactions that may occur during polymerization. The importance of branching is evident from thousands of scientific papers focused on the methodology of branching characterization and synthesis of various branched structures. The key analytical techniques for the characterization of branching are multi-angle light scattering (MALS) and viscometry of dilute polymer solutions. Although both of them can be used in a batch mode without prior sample separation, more information in much shorter time can be obtained by coupling the two techniques with an analytical separation. Size exclusion chromatography (SEC) is one of the most frequently used analytical methods used for the characterization of synthetic and natural polymers. However, SEC separation of branched polymers is often affected by their tendency to get anchored in the pores of column packing. In addition, many branched polymers contain ultra-high molar mass fractions that are prone to shear degradation in SEC columns. Asymmetric flow field flow fractionation (AF4) eliminates the anchoring and thus offers more efficient separation of branched polymers. In addition, AF4 reduces significantly the shear degradation of polymer chains. AF4-MALS thus becomes an ideal analytical tool for the characterization of polymers containing high-molar mass branched fractions such as acrylic emulsion copolymers or elastomers, while SEC-MALS remains the method of choice for smaller branched macromolecules such as for instance polymers for drug delivery, various synthetic resins, and polyamides. Both methods can be completed with an online viscometer which increases sensitivity of branching detection and extends branching studies to small polymer molecules.