Polymer structure and complexes in the lithium alkyl initiated polymerization of isoprene in the presence of 1,2-dipiperidinoethane

Bres, Philippe; Viguier, Michel; Sledz, J.; Schué, François; Black, P. E.; Worsfold, D. J.; Bywater, S.

doi:10.1021/ma00159a007

Cited by 11 publications

References 5 publications

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Anionic Polymerization

Quirk¹

2002

Encyclopedia of Polymer Science and Technology

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This article presents the fundamental principles of living anionic polymerization, including polymerizable monomers, kinetics and mechanism, stereochemistry, and copolymerization. The importance of anionic polymerization for preparation of model polymers with well‐defined structures and low degrees of compositional heterogeneity is illustrated with respect to molecular weight, molecular weight distribution, copolymer composition and comonomer distribution, stereochemistry, chain‐end functionality, and molecular architecture. Practical aspects of anionic polymerization are considered such as polymerizable monomers, solvents, and initiators. General kinetics, mechanisms, and stereochemistries of anionic polymerizations of styrenes, dienes, acrylates and methacrylates, vinylpyridines, epoxides, thiiranes, lactones, cyclic carbonates, and siloxanes are discussed. Effects of aggregation of the initiator and of the chain‐end on the kinetics of alkyllithium‐initiated polymerizations of hydrocarbon monomers are detailed. Experimental conditions that can cause chain transfer and chain‐termination reactions are presented. Copolymerization behavior, monomer reactivity ratios, and copolymer microstructure for styrenes and dienes are detailed to understand the syntheses of tapered block copolymers and random copolymers.

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Anionic Polymerization

Quirk¹

2002

Encyclopedia of Polymer Science and Technology

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Alkyllithium-initiated polymerization of butadiene in presence of a bi-1,3-dioxane derivative

1989

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Some results are reported on the alkyllithium-initiated polymerization of butadiene in cycle pentane in presence of 2,2'-bis(4,4,6-trimethy1-1,3-dioxane). The effect of this lithium chelating agent on one-unit model active centres is also reported. Comparisons are made with another highly efficient polymer structure modifier, 1 ,2-dipiperidinoethane. Conclusions are reached on the reasons why both are particularly effective in inducing the formation of polydienes having extremely high vinyl content.The large effect of solvent on the structure of polydienes produced by alkyllithium initiation was noted early in the development of anionic polymerization. The production of highly 1,4 polymers, when non-polar solvents or bulk conditions were used, was of great interest commercially'.2). Use of polar solvents such as tetrahydrofuran (THF) or diethyl ether results in polymers having a high proportion of vinyl structur e~~~~) .Relatively large fractions of such polar solvents have to be added to a nonpolar base before this change occurs, but a number of chelating compounds such as tetramethylethylenediamine (TMEDA)') or 1,2-dipiperidinoethane (DIPIP)6s7 are quite effective when added at ratios to lithium (R) around unity. Oxygen-based alkali metal ion complexing agents such as cryptands*) or diglymeg. lo) can also be used. It is, however, uncommon to obtain polymers with over 85

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Active centre structure and the stereoregulation process in anionic polymerization

Bywater

1992

Makromolekulare Chemie. Macromolecular Symposia

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The mechanism of stereoregulation in the anionic polymerization of butadiene and isoprene is discussed in terms of what is known about the structure of the active centres. This includes the effect of the presence of cis and trans isomers and the dynamics of their interconversion and in the isoprene case, the effect of two distinct types having 1.4 and 4.1 structures.The difflcult task of elucidation of the stereoregulation process is made much easier in anionic polymerization because of the good stability of the active centres under most conditions. Particularly important is the ability to characterize them by NMR spectroscopy in the form of oligomeric models but also by optical spectroscopy during actual polymerization processes. The first indication of interest mechanistically from N M R spectroscopy was the appearance of cis and trans forms of the model compounds t.bu. CH&H-CHz CH, Li+ (1) and t.bu. C--CHZC(CH,)~CH-~ L i ' (2) which mimic the active centres in butadiene and isoprene polymerizatioqrespectively. A cross-check with optical spectroscopy revealed that generally the two forms absorb at different wavelengths (trans at longer h) so that isomerization can be monitored during actual polymerization. The relative amounts of each depend on counter-ion and solvent but allylic lithium compounds generally, largely independent of the hydrocarbon chain attached, prefer the trans form in hydrocarbon solvents and cis form in polar solvents.This observation is of obvious interest in terms of the classic recipe for the preparation of highly cis-1.4 polyisoprene in non-polar solvents by lithiumbased initiation (3). One might expect that the predominant trans active centres would lead to a polymer rich in trans units. Since the exact opposite is observed then it is clear that the equilibrium state is not attained under most conditions. A study of the early stages of isoprene addition (4). together with measurements of the cis + trans isomerization rates, showed that the 0 1992 Huthig & Wepf Verlag, Basel

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Polymer structure and complexes in the lithium alkyl initiated polymerization of isoprene in the presence of 1,2-dipiperidinoethane

Cited by 11 publications

References 5 publications

Anionic Polymerization

Anionic Polymerization

Alkyllithium-initiated polymerization of butadiene in presence of a bi-1,3-dioxane derivative

Active centre structure and the stereoregulation process in anionic polymerization

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