High Resolution Dark Field of Poly(p-Phenylene Benzobisthiazole)

Abstract

The resolution attainable in polymer samples is limited by radiation damage causing crosslinking or chain scission with subsequent loss of mass. Molecules containing aromatic groups have been found to have improved resistance to beam damage, presumably due to resonance stabilization of radicals generated by the electron beam. Poly(p-phenylene benzobisthiazole) (PBT), a wholly aromatic, heterocyclic polymer used in high modulus, high strength fibers and films has been studied by tilted beam dark fieldSamples thin enough for TEM were prepared from bulk films by extraction replication with collodion and examined in a JEOL 100 CX operated at 100 KV using Kodak 4463 film. Figure 1 shows the decay of the 2nd, 3rd and 4th equatorial reflections as a function of electron dose. The intensity was assumed to be proportional to the current on the isolated observation screen when the microscope was operated in the diffraction mode and the appropriate reflections selected with a 2.8 mrad objective aperature (see Figure 1).