Studies on thermally induced structural changes in silicon based polymers by positron annihilation

Temperature dependence of positron annihilation lifetime spectra of polysil anes such as, poly(methyl-n-propylsilane) (PMPrS) and poly(di-n-hexylsilane ) (PDHS) has been investigated. The tau(3) in PMPrS is seen to increase mon otonically around the solid-liquid transition temperature. The transition t emperature and free volume are observed to depend on the molecular weight a nd/or packing of the backbones. For PDHS, a sharp change in t3 and I-3 is s een at the solid-solid transition temperature. Free volume radius probabili ty density functions, above and below the transition temperature, are prese nted in PMPrS and PDHS. Positron studies are complimented by conventional t hermal analysis studies. (C) 2000 Elsevier Science Ltd. All rights reserved .