Effect of LiClO₄ and LiCl Additives on the Kinetics of Anionic Polymerization of Methyl Methacrylate in Toluene‐Tetrahydrofuran Mixed Solvent

Abstract

The kinetics of anionic polymerization of MMA has been studied at −78 °C in toluene‐THF (9:1 v/v) using 1,1′‐diphenylhexyl lithium as initiator in the presence of lithium perchlorate and lithium chloride as Lewis acid additives. The control of the polymerization is lost in the absence of additives as evident from the non‐linear first‐order time‐conversion plot and polymers with broad multimodal molecular weight distribution. The presence of LiClO4 and LiCl in 10:1 and 5:1 ratio, respectively, over the initiator brings about sufficient control, yielding polymers of narrow unimodal distribution throughout the polymerization. The reaction in the presence of the additives follows first‐order kinetics free of termination and transfer. Moreover, the order with respect to the active centers is found to be almost unity, which signifies a probable disaggregation of ion‐pairs to a single complexed propagating species.GPC elugrams at different conversions for MMA polymerization in the presence of LiClO4.magnified imageGPC elugrams at different conversions for MMA polymerization in the presence of LiClO4.

Ion pairing effects in the zwitterionic ring opening polymerization of δ-valerolactone

“…For the anionic polymerization of MMA, the addition of lithium salts has been shown to influence both the polymerization rate and the molecular weight distribution. [32][33][34] This was proposed to be due to the ability of Li + to complex with the propagating species and break up aggregates of ion pairs. DFT calculations by Van Beylen and coworkers also suggest that LiCl prevents selfaggregation and may even stabilize active sites.…”

N-Heterocyclic olefins as initiators for the polymerization of (meth)acrylic monomers: a combined experimental and theoretical approach

“…7 In combination with further additives (Lewis acids, ligands for the counter ions) and low polymerization temperatures, a controlled polymerization can be conducted. [8][9] In view of these difficulties, a range of alternative initiating systems has been investigated with the overall aim of increasing the livingness of the polymerization and reducing the complexity of the reaction setup. Major contributions include tailoring of the aggregation equilibria by application of coordinating additives (both of the counter ion and the enolate), 10 the development of group-transfer polymerization 11 and the use of metal-free counter ions, [12][13][14][15] as well as discrete organometallic porphyrin- [16][17] or metallocenebased [18][19][20] catalysts.…”

Diastereoselective Alkylation of β-Amino Esters: Structural and Rate Studies Reveal Alkylations of Hexameric Lithium Enolates

“…Alkylation of enolate 9 derived from either ammonium tosylate 2 or free base 6 provides similar diastereoselectivities. However, free base 6 offered considerable advantages for the structural and mechanistic studies by affording solutions of enolate 9 that were free of LiOTs. − Treatment of 6 with 1.0 equiv of LiHMDS effected the quantitative conversion of 6 (1740 cm -1 ) to enolate 9 (1618 cm -1 ) followed by in situ IR spectroscopy . Also, we used BnBr as the electrophile instead of 3 to study the alkylation mechanism.…”

“…Indeed, enolate 9 appeared to form mixed aggregates with a number of lithium salts causing minor autocatalysis and autoinhibition. Nonetheless, such salt effects probably influence the majority of organolithium reactions, − and the scarcity of mechanistic insights is conspicuous…”