Transmission electron microscopy of saturated hydrocarbon block copolymers

Contrast for transmission electron microscopy (TEM) of microphase‐separated saturated hydrocarbon diblock copolymers has been obtained using ruthenium tetroxide (RuO4). This technique exploits differences in the rate of transport of the oxidizing stain in rubbery amorphous versus semicrystalline, or glassy, microdomains. Rapid quenching from above the melting (Tm), or glass transition (Tg) temperature is shown to preserve the equilibrium melt morphology in poly(ethylene)‐poly(ethyl‐ethylene) (PE‐PEE), poly(ethylene)‐poly(ethylene‐propylene) (PE‐PEP), and poly(vinylcyclohexane)‐poly(ethyl‐ethylene) (PVCH‐PEE) diblock copolymers; PE melts at 108°C, PVCH is glassy up to about 140°C, while PEE and PEP remain rubbery down to approximately‐20°C and −56°C, respectively. Treatment of ultrathin sections of the quenched specimens with RuO4 vapor led to welldefined TEM images, that revealed microdomain type and order. These results are consistent with SANS data taken under equilibrium conditions.