Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

Abstract

The anionic polymerization of methyl methacrylate using tetraphenylphosphonium triphenylmethanide as an initiator proceeds in a living manner even at room temperature. The rate constants of propagation were measured between −20 and +20 °C using a flow tube reactor. At 0 °C the reaction half-lives range from 0.3 to 1 s. The polymerization follows first-order kinetics with respect to monomer conversion (with a short induction period) and shows a linear dependence of the number-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 center concentration is consistent with the coexistence of ion pairs and free ions. The Arrhenius parameters obtained in the temperature range from −20 °C to +20 °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 orders of magnitude smaller than those expected for such a large cation, indicating a large fraction of dormant species. NMR and quantum-mechanical studies of a model compound confirm the presence of a dormant ylide in equilibrium with a small amount of enolate ion pairs.

Anionic polymerization of methyl methacrylate using tetrakis[tris(dimethylamino)phosphoranylidenamino] phosphonium (P5+) as counterion in tetrahydrofuran

“…5 shows the Arrhenius plot of the propagation rate constants, k p , compared to other counterions. The rate constants in presence of the P 5 + cation are much higher than those obtained with metal cations 1) and even higher than for the tetraphenylphosphonium ion where dormant ylides have been shown to be the majority of species 36) . Ylide formation is not possible for the P 5 + cation.…”

“…Zagala and Hogen-Esch 35) successfully used the tetraphenylphosphonium (TPP + ) counterion in the polymerization of MMA and obtained polymers with narrow molecular weight distribution at ambient temperature. Our kinetic studies 36) supplemented by NMR evidence 37) revealed that TPP + ion pairs are in a dynamic equlibrium with dormant ylides.…”

“…All experiments were carried out in a specially designed flow-tube reactor with a mixing time of a 1 ms and reaction times of 4 ms f s f 0.6 s 23,36,45) . The effective temperature, T eff , of each experiment was determined using Eq.…”

“…One possibility is the use of various ligands in conjunction with classical anionic initiators. r-Ligands, such as crown ethers 6) , cryptands 7,8) , tertiary amines 9,10) ; l-ligands, such as alkali alkoxides 11,12) halides 2, 13) , perchlorates 14,15) , aluminum alkyls [16][17][18][19] , and r, l-ligands, such as alkoxyalkoxides [20][21][22][23] , aminoalkoxides 24) , and silanolates [25][26][27] have been used with much success.…”

The effect of TMEDA on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran using lithium as counterion

“…All experiments were carried out in a specially designed flow-tube reactor with a mixing time of a 1 ms and reaction times of 2 ms f s s 20 s. [15,[33][34][35] The effective temperature, T eff , of the each experiment was determined using Eq. (1) [36] T eff = T m + 0.55 DT…”