Quantitative compositional mapping of core-shell polymer microspheres by soft X-ray spectromicroscopy

Core-shell polymer microspheres have been prepared by a two-step precipitat ion polymerization. These microspheres consist of 3.2 mum polydivinylbenzen e-55 (DVB55) cores coated with similar to0.4- 0.9 mum wide shells composed of poly(DVB55-co-EDMA), a random copolymer of DVB55 and ethylene glycol dim ethyl acrylate (EDMA). The chemical composition, core-shell morphology, and porosity of these structured microspheres have been studied quantitatively with scanning transmission X-ray microscopy (STXM) at a spatial resolution of 100 nm. Images recorded at selected energies through the C Is absorptio n region were analyzed using singular value decomposition to obtain quantit ative maps of the DVB55 and EDMA components. The EDMA concentration in the shell determined by STXM was found to be in good agreement with that predic ted from the comonomer composition over the range of 10-90% EDMA. The preci sion of chemical quantification at high spatial resolution is shown to be a dequate for STXM to be useful in guiding the development of structured poly meric systems for particular applications.