Tris(2,4,6-trimethoxyphenyl)phosphine (TTMPP) as Potent Organocatalyst for Group Transfer Polymerization of Alkyl (Meth)acrylates
Résumé
Several commercial trialkyl phosphines were tested as organic catalysts for the group transfer polymerization (GTP) of methyl methacrylate (MMA) and tert-butyl acrylate (tBA). Among them, only tris(2,4,6-trimethoxyphenyl)-phosphine (TTMPP) was able to bring about the "controlled/living" GTP of both monomers at room temperature, in bulk and/or in THF solution, using 1-methoxy-2-methyl-1-[(trimethylsilyl)oxy]prop-1-ene (MTS) as initiator. However, control of the polymerization appeared to be more difficult in the case of tBA compared to MMA. Poly[alkyl(meth)acrylate]s exhibiting dispersities <1.37 in bulk and <1.45 in THF, and molar masses in good accordance with the initial [monomer](0)/[MTS](0) molar ratio could thus be obtained in quantitative yields. Poly(methyl methacrylate)-b-poly(tert-butyl acrylate) block copolymers, with final dispersity <1.2 and controlled molar masses, were also synthesized by sequential TTMPP-catalyzed GTP. First order kinetics plot of the GTP of MMA revealed an induction period of a few hours, which strongly depended on the initial polymerization conditions. The tacticity of the final PMMA's (mm/mr/rr = 0.06/0.42/0.52) were very similar to that of an anionically derived PMMA. These data are in favor of the occurrence of a dissociative mechanism, forming minute amounts of true enolate-type propagating species, during the TTMPP-catalyzed GTP of MMA in THF. Analyses by C-13 and Si-29 NMR spectroscopy at room temperature of 1/1 molar MTS/TTMPP mixtures did not show the formation of enolate-type species.