Direct imaging of polyethylene crystallites within block copolymer microdomains

Ruthenium tetroxide (RuO4) is a versatile agent for imparting mass density contrast to saturated hydrocarbon polymers. We have successfully employed R uO4 to examine the microdomain and crystallite morphologies of poly(ethylen e-block-vinylcyclohexane) semicrystalline-glassy diblock copolymers via tra nsmission electron microscopy (TEM). Ultrathin sections cut from blocks sta ined with RuO4 showed excellent contrast in TEM, revealing the individual p olyethylene crystallites that formed within the preexisting block copolymer microdomains. The size and orientation of the crystallites, which previous ly could only be inferred from scattering data, are readily apparent in the micrographs. Moreover, such imaging directly reveals the lateral extent of the crystallites and the number of crystallites lying within the cross sec tion of each microdomain. (C) 2000 John Wiley & Sons, Inc.