Study of ion beam induced depolymerization using positron annihilation techniques

Ion beam induced depolymerization of polymers is a special class of ion beam induced chemical reaction which gives rise to catastrophic "unzipping" of macromolecules with production of large amounts of the monomer, of the order of many hundreds monomer molecules per each macromolecule. The possible modification of the density at microscopic level prompted us to undertake a study of this effect utilizing positron annihilation techniques in Poly(methylmethacrylate) (PMMA) before and after bombardment with He(+) 300 keV ions at 200 degreesC. Preliminary results shown here indicate that before bombardment there is a reproducible dependence of nano-hole distribution on the sample history. Moreover at 200 degreesC we do not detect formation of new cavities as a consequence of the strong depolymerization that occurs under the ion beam. The possible correlation of these findings with transport properties of PMMA at temperature higher than the glass transition temperature will be discussed. (C) 2001 Elsevier Science B.V. All rights reserved.