Various strategies for the chemical transformation of xanthate-functional chain termini in MADIX copolymers

Although the MADIX process is undoubtedly one of the most promising controlled free radical polymerization technique for an industrial development, one of its potential drawback may lie in the fact that the xanthate terminal group, if not deactivated, is likely to be degraded during the lifetime of the polymer or under some specific application conditions. Several appropriate treatments were developed by our group in order to prevent an uncontrolled degradation over time which may eventually generate low molecular weight malodorous, potentially toxic sulfur-based by-products. For instance, the radical reduction of xanthate terminal groups of PDMS and MADIX polymers was efficiently conducted with peroxide and percarbonate initiators in secondary alcohols, e.g. isopropanol. The thermally-induced elimination of xanthate terminal groups of MADIX polymer chains was also successfully accomplished using five different secondary xanthates. This allowed the generation of terminal thiol groups for PDMS and MADIX polymers.