Kinetics and mechanism of group transfer polymerization of N‐butyl acrylate catalyzed by Hgl₂/(CH₃)₃Sil in toluene

Abstract

The group transfer polymerization (GTP) of n-butyl acrylate (nBuA) using 1-methoxy-1-(trimethylsiloxy)-2-methyl-l-propene (MTS) as an initiator, mercuric iodide (Hg ) as a catalyst in toluene at room temperature gves a vely good control of molecular weiat and narrow molecular weight distribution. (q, < 1.2). Kinetic studies in this system reveal that this reaction is rather slow, half-lives bemg in the range of hours. The kinetic order of the apparent rate constant of propagation with respect to initiator and catalyst concentrations were found to be near to unity. However, the first-order timeconversion plots exhibit considerable induction periods. Upon addition of trimethylsilyl iodide (TMSI) the induction periods vanish and the rates are increased by two orders of magnitude. The reaction is first-order with respect to TMSI indicating that it takes part in the reaction by activating the catalyst. The complex from HgI and TMSI acts as a nucleophilic catalyst, similar to oxyanions in the GTP of MMA in kF. It is proposed that the induction periods are due to the formation of TMSI from MTS and Hg12.

Polymerization of Polar Monomers Mediated by Main-Group Lewis Acid–Base Pairs

“…Brønsted acids are also included in this discussion as they serve as a reagent or precatalyst to generate an LA (R 3 Si + ) as the true catalyst upon protonation of the SKA initiator (vide infra). In the early stage of the GTP development, inorganic LAs such as zinc halides, aluminum halides, and oxides were used to activate the SKA initiator for the polymerization of more reactive acrylates, with higher catalyst loadings (typically 10–20 mol % relative to the monomer). , The living polymerization of acrylates with low catalyst loadings was achieved by the HgI 2 /Me 3 SiI system (5.2 mol % HgI 2 and 2.1 mol % Me 3 SiI relative to the initiator). − …”

B(C6F5)3-Catalyzed Group Transfer Polymerization of Acrylates Using Hydrosilane: Polymerization Mechanism, Applicable Monomers, and Synthesis of Well-Defined Acrylate Polymers

“…To date, the GTP catalyzed by Lewis and Brønsted acids has been one of the most efficient methods for synthesizing well-defined acrylate polymers, especially when acidic organocatalysts are used, though basic catalysts of some organic N -heterocyclic carbenes could afford moderate control over molecular weight and molecular weight distribution of alkyl acrylate polymers. − The GTP of acrylate monomers using conventional Lewis acids, such as ZnX 2 (X = Cl, Br, and I), − organoaluminums, ,, HgI 2 + R 3 SiI, − CdI 2 + R 3 SiI, Yb­(OTf) 3 , and Sc­(OTf) 3 , produced defect-free acrylate polymers. However, a significant amount of the catalyst (10–20 mol % relative to monomer) was required though the polymer products with low molecular weights were formed, e.g., usually no greater than 10000 g mol –1 , due to the low Lewis acidity of such transition metal compounds.…”

Organocatalyzed Group Transfer Polymerization

“…Given that the initiation and propagation reactions during a GTP process are in principle rooted in the iteration of the elementary organic reaction, i.e., the Mukaiyama–Michael reaction,22–24 either a Lewis base or a Lewis acid has to be utilized as the catalyst of the GTP. Prior to 2007, the conventional Lewis bases of anionic nucleophiles, such as SiMe 3 ,22,25,26 ,22,25–27 CN − ,22,25,28,29 ,22,28 F − ,26,28,29 oxyanions,30,31 and hydrogen bioxyanions31,32 featuring a sterically hindered bulky counter cation like tris(dialkylamino)sulfonium or tetraalkylammonium, and the Lewis acids of transition‐metal compounds, such as ZnX 2 (X = Cl, Br, and I),27,29,33,34 organoaluminums,27,29,35 HgI 2 + R 3 SiI,24,36–42 CdI 2 + R 3 SiI,34 Yb(OTf) 3 ,43 and Sc(OTf) 3 ,43 dominated. Notably, the anionic nucleophiles associated with bulky non‐metallic cations are actually metal‐free, and can in a sense be viewed as the initial organocatalysts used in the GTP field.…”