In the group-transfer polymn. (GTP) of Me methacrylate with dimethylketene Me trimethylsilyl acetal (I) [31469-15-5] or trimethylsilyl nitrile [7677-24-9] as initiator in MeCN, tris(dimethylamino)sulfonium difluorotrimethyl silicate [59218-87-0] was preferred as coinitiator in comparison to Et4NCN because it did not react with the monomer. Furthermore, there was a reaction between the solvent and I and probably also the propagating chains, diminishing the active centers in polymn. Therefore MeCN was unsuited as solvent in the GTP. With an unreactive solvent the living character of GTP would become clearer.