Study of the Propagation Center in the Anionic Polymerization of (Meth)acrylic Monomers:  NMR and MNDO Study of the Complexes of Di-tert-butyl 2-Lithio-2,4,4-trimethylglutarate and of the Living Poly(tert-butyl methacrylate) Oligomers with Lithium Chloride

Abstract

Interactions of living oligomers of tert-butyl methacrylate (tBuMA) with a Li counterion and of the model living dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) with LiCl (B) were studied in tetrahydrofuran-d 8 (THF-d8) solution by 7 Li, 6 Li, 1 H, and 13 C, 1D and 2D, NMR spectroscopy. Di-tertbutyl 2-lithio-2,4,4-trimethylglutarate is shown to form a 1:1 complex with lithium chloride in THF. 1 H, 7 Li NMR results suggest that a rapid equilibrium between free LiCl and the mixed complex takes place when the molar ratio LiCl:lithiated dimer is higher than 1. From 13 C relaxation times, a dimeric aggregation (i.e. A2B2) of the complex is deduced, in full accord with MNDO calculations. Preliminary results are presented for living tBuMA oligomers prepared by initiation with diphenylhexyllithium in the presence of various amounts of lithium chloride. Fast-acquired 13 C NMR spectra of the living ends were recorded using 13 C-enriched monomer added at the end of the polymerization. Their structure is shown to be affected by the amount of LiCl added and to correspond to an equilibrium between free lithium chloride and a complexed end group. A higher excess of LiCl apparently does not change the nature of the complexed living end. The oligomers exhibit marked self-termination in THF at 273 K. Finally, a correlation of the structure of the living chain ends with the macromolecular parameters of the resulting polymer is attempted.

Anionic polymerization of methacrylic monomers: characterization of the propagating species

“…Measurements of 13 C relaxation times agree with the dimeric aggregation (i.e. Dimer 2 LiCl 2 ) of the (1:1) complex, consistent with MNDO calculations [94]. Fig.…”

“…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]. LiCl has been reported to affect the tacticity of PtBMA.…”

“…In case of acrylates, however, the addition of LiCl has no favorable effect on the selftermination rate [95]. The structure of the actives species complexed by LiCl has been analyzed by Zune et al [94] Rapidly acquired 13 C NMR spectra have been recorded for living tBuMA oligomers initiated by DPHLi in the presence of various amounts of LiCl and terminated by a few 13 C-enriched monomers. The structure of the lithium ester enolate is affected by the amount of LiCl and fits an equilibrium between free lithium chloride and complexed active endgroups.…”

Recent developments in anionic polymerization

“…For these reasons, living poly(tert-butyl-methacrylate) (PtBMA), stable at 0°C, and its dimeric model, di-tert-butyl 2-lithio-2,4,4'-trimethylglutarate (DBTMGLi), have been recently studied [31,32]. The last monomer units of PtBMA have also been selectively labeled by 13 C) of both the dimeric model and the growing chains has been conducted in the absence and presence of μ-and μ/σ-type ligands [33,34], the main conclusions of which are as follows:…”

Controlled Anionic Block Copolymerization with N,N‐Dialkylacrylamide as a Second Block

“…[15] The influence of LiCl on the polymerization of acrylates and methacrylates has been described in a number of experimental [15][16][17][18][19] and theoretical [20] papers. In general narrower MWD were obtained when using LiCl as additive.…”