COUNTERION EFFECTS IN THE ANIONIC-POLYMERIZATION OF METHYL-METHACRYLATE - MECHANISTIC RELEVANCE TO GTP

The room temperature polymerization of methyl methacrylate (MMA) by th e cesium or tetrabutylammonium salt of 9-methylfluorenide proceeds in an uncontrolled fashion. To understand these results, we have studied the structure of the propagating chain-ends using polymer microstructu re and stopped-flow FT-IR spectroscopy of model compounds. Deprotonati on of methyl isobutyrate with the cesium salt of 1,1,4,4-tetraphenylbu tane dianion afforded the corresponding cesium enolate (mu=1645 cm(-1) ). The deprotonation of methyl 2,2,4-trimethyl-4,6-dicarbomethoxyhept- 6-en- 1-oate (the trimeric ester of MMA) was accompanied by a rapid (2 -4 s) intramolecular cyclization. Comparison of group transfer polymer ization (GTP) to anionic polymerization reveals that the counterion is important but probably not the sole mechanistic feature responsible f or the Living behavior of GTP.