Various types of polysiloxanes studied by positron annihilation lifetime spectroscopy

In the work, linear poly(vinylsiloxanes) with regular distributions of vinyl groups along chains, the networks obtained by their hydrosilylation with various hydrogensiloxanes, products of pyrolysis of such networks as well as the networks prepared via reaction of low-molecular siloxanes have been studied by positron anihilation lifetime spectroscopy (PALS). on free volume sizes determined by this method, relations between cross-link densities in the investigated systems have been established. They have been compared with the results of swelling experiments conducted in the work and to efficiency of cross-linking reaction evaluated in our previous FTIR investigations of the systems. It has been found that PALS and swelling measurements lead to the same conclusions concerning cross-link densities in the networks prepared from low-molecular siloxanes. Discrepancies have been observed in the case of polymer-derived systems. Additionally, it is demonstrated that PALS is capable of revealing the presence of free carbon phase in SiCO materials formed upon pyrolysis of polysiloxane networks.