AN1301: PLGA Molar Mass and Conformation by SEC-MALS-IV

The characterization of PLGA by means of conventional size exclusion chromatography (SEC) is problematic because of the lack of suitable calibration standards. In addition, the linear polyester structure can be modified by the addition of small amounts of polyfunctional monomer to obtain branched chains of differing degrees of branching. The degree of branching becomes an additional parameter that can be used to adjust PLGA properties—all of which renders conventional column calibration an inadequate analytical technique.

In this application note, two commercially available samples were analyzed by SEC coupled to a DAWN^®, Optilab^®, and ViscoStar^®. The MALS and RI signals were combined to determine absolute molecular weight, independently of elution time or column calibration. The ViscoStar was used in order to measure intrinsic viscosity (IV) and uncover additional information about the molecular structure of the analyzed polymers. In addition to molar mass distributions, the SEC-MALS-IV system yields the relationship between intrinsic viscosity and molar mass (Mark-Houwink-Sakurada plot) that can provide deeper insight into the molecular structure of the polymers being analyzed.