Effect of Lithium Chloride on the "Living" Polymerization of tert-Butyl Methacrylate and Polymer Microstructure Using Monofunctional Initiators

Abstract

The effect of LiCl on the anionic polymerization of tert-butyl methacrylate (tBuMA) initiated with monofunctional alkali metal-based carbanionic species was investigated at -78 °C in THF. The propagation rate of the polymerization process was determined by gas chromatography and by gravimetry. It was found that, in the presence of LiCl in a molar ratio of 5 with respect to the initiator, the rate constant, k9, is 20 times lower than that in the absence of LiCl. The polymers and oligomers were analyzed by size exclusion chromatography (SEC) and 13C NMR spectroscopy. The polymers obtained in the absence of LiCl had broad molecular weight distributions and contained significant amounts of oligomers, while those obtained in the presence of LiCl were monodisperse, without any noticeable oligomers. 13C NMR showed that the isotactic content of the polymers increased significantly when the molar ratio of LiCl to the initiator was higher than 2. The effect of LiCl on the rate constant and on the microstructure of the polymers was attributed to complex formation between LiCl and the living polymer chains.* To whom all correspondence should be addressed. 1 This article is dedicated to Professor Ph. Teyssié on the occasion of his retirement from academic life.

Anionic polymerization of methacrylic monomers: characterization of the propagating species

“…However, at LiCl/RLi molar ratios higher than 2, k p decreases as the LiCl content is increased. The same observation was reported by Varshney et al for the anionic polymerization of tBMA in presence of LiCl [96], the effect of LiCl being however more drastic in this case (Table 6). Müller et al [97] have suggested that a 1:1 adduct would coexist with a less active 2:1 adduct (Scheme 15) [95], which has been recently debated [94].…”

“…Indeed, the content of isotactic placements is increased by 10% when a threefold molar excess LiCl is added to RLi. [96] No effect is however observed in case of PMMA, which remains unexplained. LiCl leads to a decrease in chain polydispersity when MMA and tBMA are polymerized in THF at low temperatures, and the mechanism is apparently living.…”

Linking reactions of living polymers with bromomethylbenzene derivatives: Synthesis and characterization of star homopolymers and graft copolymers with polyelectrolyte branches

“…Polymerization of tert-butylmethacrylate in THF at Ϫ78°C resulted in polymers with fairly broad (by the standards of anionic polymerization) molecular weight distributions 51 (M w /M n ϭ 1.3), making it difficult to resolve the SEC peaks corresponding to the star and arm. The chromatogram exhibited rather broad peaks, where the different polymeric species could not be separated easily.…”

“…LiCl can be used to control the polymerization reaction by avoiding undesirable side reactions and to reduce the molecular weight distribution as demonstrated in previous studies. 51,52 LiCl also has another effect: It reduces the rate of the linking reaction. [51][52][53][54][55] It is documented that in the case of PtBuMA, LiCl forms -type complexes with the living polymer chains, reducing the propagation rate by a factor of 20 when compared to the rate in its absence.…”

“…51,52 LiCl also has another effect: It reduces the rate of the linking reaction. [51][52][53][54][55] It is documented that in the case of PtBuMA, LiCl forms -type complexes with the living polymer chains, reducing the propagation rate by a factor of 20 when compared to the rate in its absence. LiCl has little effect on the polymerization rate of MMA, probably because the -complexes formed are not as stable.…”