Results of group transfer polymn. of Me acrylate (I) in MeCN with 1-methoxy-1-propenyloxytrimethylsilane (II) as initiator and tris(dimethylamino)sulfonium difluorotrimethylsilicate, tris(piperidino)sulfonium difluorotrimethylsilicate, tris(dimethylamino)sulfonium bifluoride, tris(piperidino)sulfonium bifluoride, Bu4NF.3H2O, and Et4NCN as catalysts are presented. Difluorotrimethylsilicate- and bifluoride-derived catalysts are more active than fluoride- and cyanide-derived ones, and lead to higher but in no case complete conversion. Polymers with no.-av. mol. wts. (-Mn) ?10,000 and polydispersity indexes (.hivin.Mw/.hivin.Mn) >= 1.3 can be prepd. Mol. wt. control is poor and not possible without calibration of reaction conditions, since all catalysts activate side reactions of I (to low-mol.-wt. compds. and oligomers) of II and (as is assumed) also of growing chains with the solvent MeCN under termination.