In the morphological characterization of polymer materials via transmission electron microscopy the greatest challenge is most often obtaining imaging contrast rather than imaging resolution. The structures of interest are often on a nanometer length scale and thus easily resolvable with TEM provided a contrast mechanism exists. However, the light element composition of most polymers (predominantly C, H, and sometimes N and O) provide no atomic number (Z) contrast. Traditionally, imaging contrast has been obtained for some polymer systems through the use of heavy metal containing stains such as OsO4, RuO4 or uranyl acetate. These methods require differences in reactivity with the stains in different morphological regions due either to differences in chemical functionality (e.g. OsO4 staining of PS-PI block copolymers) or differences in the permeability to the stain (e.g. RuO4 staining of semicrystalline polyolefins). Useful though they are, these staining methods do not work for some important classes of polymers, such as polyurethanes with MDI or TDI hard segments and PEO soft segments. TEM using an in-column, imaging, energy filter provides an alternative to conventional staining and can be used, for instance to resolve the hard and soft segments of polyurethanes based on electron energy loss contrast due to the presence of nitrogen in the hard segments and its absence in the soft segments. New block copolymer materials of poly(isoprene-b-benzofulvene) (PI-PBF) are of interest because of the high Tg of the PBF hard domains, relative to conventional PI-PS materials. However, morphological characterization of PI-PBF is challenging using traditional staining methods since both blocks contain non-aromatic double bonds. The PBF blocks, however, are labile to attack at an acidic proton that allows functionalization with light hetero atoms and this allowing TEM imaging of the morphology with energy filtered TEM.

Energy filtered TEM for element specific imaging of new poly(isoprene-b-benzofulvene) block copolymers

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.