Stereochemical control in anionic polymerization of 2‐vinylpyridine and related vinyl monomers

Abstract

The alkylation, silylation and other electrophilic reactions of l-lithio-l,3-bis(2-pyridyl)butane (2a) in THF at -78 "C leads to meso-like products that may be accounted for by intramolecular coordination of Li ion with the penultimate 2-pyridyl group. This is also demonstrated by proton-transfer equilibria between l-lithio-2ethylpyridine and 2a, allowing the determination of the AH and AS of intramolecular chelation in 2a. The AS of chelation is nearly zero, probably as a result of chelation-induced desolvation of Li ion. Surprisingly, however, the corresponding addition of 2-vinylpyridine to 2a and higher P2VPLi homologs in THF is not stereoselective. In toluene at -78 "C the t-BuLi-initiated polymerization of 2-VP is actually somewhat syndiotactic (rr=0.44). The presence in this polymerization of at least one equivalent of t-BuOLi or other tertiary ROLi surprisingly leads to isotactic P2VP. SEC viscometric and other studies indicate that both the P2VPLi-and P2VPLi-ROLi complexes are monomeric in toluene. The stereochemistry is apparently due to a 1 : 1 P2VPLi-ROLi complex that discriminates between the two pro-chiral faces of the anion by preferential coordination of the (ROLi,) moiety to the meso-prochiral face. Isotactic-like addition now occurs by electropbilic attack of 2-VP that is syn with respect to the (ROLi,) 'counter ion.'

A Mechanism for Electropolymerization of 2-Vinylpyridine Coatings on Metal Surfaces

“…Electropolymerization of vinylpyridines has attracted considerable attention due to important applications in modified electrodes, − microelectronic transistors, , matrixes for incorporating electroactive groups at electrode surfaces, , polyelectrolytes, , and corrosion inhibitors. − Most of the research so far, however, has focused on these new materials and the measurement of their polymer and coating properties. − Little research has been carried out to study the mechanisms of coating formation by electropolymerization. This lack of understanding of the mechanisms may have contributed to poor-quality coatings and poor reproducibility. ,, …”

“…[11][12][13] Most of the research so far, however, has focused on these new materials and the measurement of their polymer and coating properties. [14][15][16][17][18][19][20] Little research has been carried out to study the mechanisms of coating formation by electropolymerization. This lack of understanding of the mechanisms may have contributed to poor-quality coatings and poor reproducibility.…”

Living tert‐butyllithium initiated anionic polymerization of 2‐vinylnaphthalene in toluene‐tetrahydrofuran mixtures

“…It is possible that this is because of the relatively long lifetime of these oligomer anions that, in its own turn, may be the result of the interaction of the propagating ion pair with a penultimate 2‐naphthyl unit. The stabilization of the propagating ion pair by cation coordination with penultimate pendent groups is well known,10, 11 although the coordination of hydrocarbon‐pendent groups to our knowledge has not been reported.…”

Controlled radical polymerization catalyzed by CuCl/BDE complex in water medium. II. Polymerization of methyl methacrylate and formation of PMMA with bimodal molecular weight distribution

“…Multi‐MWD of polymers induced by multiactive species in systems were observed to be rather common in anionic polymerizations 15–17. In the BDE/CuCl system, based on the corresponding “coordinated radical cage” mechanism,12 the reversible equilibrium of coordinated radical cage species {R • + CuCl 2 /BDE} (I) and the common free radical (II) could coexist (Scheme ).…”

“…Multi-MWD of polymers induced by multiactive species in systems were observed to be rather common in anionic polymerizations. [15][16][17] In the BDE/CuCl system, based on the corresponding "coordinated radical cage" mechanism, 12 the reversible equilibrium of coordinated radical cage species {R • ϩ CuCl 2 /BDE} (I) and the common free radical (II) could coexist (Scheme 1). Based on Scheme 1, increasing the catalyst concentration of BDE/CuCl will shift the equilibrium to the right side, i.e., benefit to the formation of species (II), which implicates the relative content of species in emulsion circumstance should be affected.…”