MORPHOLOGY AND ELECTRON-IRRADIATION BEHAVIOR OF POLY(DIMETHYL SILYLENE)

We have obtained and studied the first single crystals of the important silicon-backbone polymer, poly(dimethyl silylene) (PDMS), by dissolution in alpha-chloronaphthalene at 251-degrees-C and growth at 238-degrees-C. The crystals consist of molecularly folded, rhombic-shaped lamellae, analogous to those of carbon-based polymers. Electron diffraction patterns revealed a weak positional disorder in the intermolecular packing along the b crystallographic axis. The sensitivity of PDMS to electron irradiation was found to be substantially higher than that of typical polymers (e.g. polyethylene), with early structural changes seen at doses as low as 6 C m-2. By examining changes in composite electron diffraction reflections with radiation dose, we obtained evidence for two competing mechanisms in PDMS and showed that chain scission is much more extensive than crosslinking.