|122. Baskaran, D.; Müller, A.H.E.: Anionic polymerization of methyl methacrylate using tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium (P5+) as counterion in tetrahydrofuran, Macromolecular Rapid Communications 21, 390 (2000) -- DOI: 10.1002/(SICI)1521-3927(20000401)21:7<390::AID-MARC390>3.0.CO;2-B|
A novel metal-free initiator, i.e. the salt of the tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium (P5+) cation with the 1,1-diphenylhexyl (DPH-) anion was prepared by cation metathesis. It initiates a very fast and controlled anionic polymerization of methyl methacrylate in THF. Kinetic investigations between -20 and +20°C using a flow tube reactor provide nearly linear first-order time-conversion plots with half-lives below 0.1 s, a linear dependence of the number-average degree of polymerization, and rather narrow molecular weight distributions (Mw/Mn < 1.2). 13C NMR measurements on a model of the active chain end (the P5+ salt of ethyl isobutyrate) in THF-d8 show 15 and 25 ppm upfield shifts of the a-carbon compared to the dimers and tetramers of the lithium ester enolate, respectively, indicating a non-aggregated structure and an increased charge density on the a-carbon.