KINETIC INVESTIGATION ON METAL-FREE ANIONIC-POLYMERIZATION OF METHYL-METHACRYLATE USING TETRAPHENYLPHOSPHONIUM AS THE COUNTERION IN TETRAHYDROFURAN

The anionic polymerization of methyl methacrylate using tetraphenylpho sphonium triphenylmethanide as an initiator proceeds in a living manne r even at room temperature. The rate constants of propagation were mea sured between -20 and +20 degrees C using a flow tube reactor. At 0 de grees C the reaction half-lives range from 0.3 to 1 s. The polymerizat ion follows first-order kinetics with respect to monomer conversion (w ith a short induction period) and shows a linear dependence of the num ber-average degree of polymerization on conversion with high initiator efficiencies and narrow molecular weight distributions (M(w)/M(n) < 1 .1). The dependence of the measured rate constants on the active cente r concentration is consistent with the coexistence of ion pairs and fr ee ions. The Arrhenius parameters obtained in the temperature range ho m -20 degrees C to +20 degrees C (activation energy, E(a) = 28 kJ mol( -1) and frequency exponent, log A = 7.9) are similar to those for the Li+ cation. The determined rate constants for the ion pairs are 1-2 or ders of magnitude smaller than those expected for such a large cation, indicating a large fraction of dormant species. NMR and quantum-mecha nical studies of a model compound confirm the presence of a dormant yl ide in equilibrium with a small amount of enolate ion pairs.