Anionic Polymerization of (Meth)acrylates in the Presence of Tetraalkylammonium Halide−Trialkyl Aluminum Complexes in Toluene. 3. Kinetic Investigations on Primary Acrylates

Abstract

The polymerization of n-butyl acrylate initiated by ester enolates in the presence of tetraalkylammonium halide−trialkylaluminum complexes, R4N[Al n R‘3 n X] (n = 1, 2), in toluene has a controlled character at −78 °C only for selected combinations of the complex. Quantitative monomer conversions are usually reached with Me4N[Al n Bui 3 n Cl] leading to polymers with narrow molecular weight distributions (M w/M n < 1.2). Kinetic investigations show a complex mechanism of the polymerization, implying an equilibrium between at least two active species. Besides, various acrylate homopolymers and block copolymers (PMMA-b-polyacrylate) can be synthesized with this new initiating system.

Chain Termination and Transfer Reactions in the Acrylate Polymerization by a Monometallic Chiral Zirconocenium Catalyst System

“…Increasing the steric protection of the carbonyl carbon of alkyl acrylates apparently does not play a measurable role in suppressing the backbiting cyclization in the current system because the polymerization of tert -butyl acrylate behaves similarly to that of the n -butyl acrylate polymerization. The acrylate-derived cyclic β-ketoester structure exists predominately in its enol form, and the proton of such an enol form in cyclic structures B or C produced in the current system can be readily identified in the 1 H NMR spectrum of the P( n -BA) produced with two small peaks at 12.21 and 12.46 ppm. , Reinitiation of a cyclic β-ketoester-terminated polyacrylate chain end ( B -type structure) and subsequent formation of multiple cyclic β-ketoester-terminated polyacrylate chain ends ( C -type structure) have been previously observed in the anionic polymerization of n -BA by a three-component system consisting of ethyl α-lithioisobutyrate/tetralkylammonium halide/trialkylaluminum . What needs to be further confirmed in this overall mechanism, however, are the products of the backbiting cyclization and the reaction involving resting intermediate D and ROH.…”

“…20,21 Reinitiation of a cyclic β-ketoester-terminated polyacrylate chain end (B-type structure) and subsequent formation of multiple cyclic β-ketoesterterminated polyacrylate chain ends (C-type structure) have been previously observed in the anionic polymerization of n-BA by a three-component system consisting of ethyl R-lithioisobutyrate/ tetralkylammonium halide/trialkylaluminum. 22 to be the thermodynamic products. To determine the products of the reaction between resting intermediate D and ROH, an authentic sample of cationic zirconocenium tert-butoxide complex 3 was prepared, and a model reaction was carried out (Scheme 4).…”

Ligand Effects in Organoaluminum Catalysts for the Tacticity Control in the Synthesis of Isotactic Poly(methyl methacrylate)

“…7 Chiral metallocene complexes have been used by several groups to promote the isospecific polymerization of MMA. 8 More recently, Mu ¨ller and co-workers completed an elegant series in which additives such as cesium 9 and tetraalkylammonium halides 10 and lithium salts 11 were used to modify kinetics and resulting polydispersity of the organoaluminum-mediated anionic polymerization of methacrylates.…”

Syndio-rich poly(methyl methacrylate) from the anionic polymerisation of methyl methacrylate in the presence of novel organoaluminium amides

“…The strong influence of the Lewis acidity of the aluminium species was demonstrated by Schlaad and Mu ¨ller, 10 and also by Bolig and Chen. 5 More recently, Mu ¨ller and coworkers undertook a study in which additives such as caesium 11 and tetraalkylammonium halides 12 and lithium salts 13 were used to modify the kinetics and resulting polydispersity of the organoaluminium-mediated anionic polymerizations of methacrylates. A Density Functional Theory (DFT) study taking into account solvation effects in THF showed that solvated dimers were the most stable state of lithium ester enolates except when a cryptand ligand was present in which case the ligand-separated triple ion pair was of comparable stability.…”