Influence of the concentration of growing chains on the polymerization rate of butadiene and the microstructure of the polymer formed in the polybutadienyllithium‐butadienealiphatic hydrocarbon system

Шаманин, В. В.; Melenevskaya, E. Yu.; Sgonnik, Vladimir

doi:10.1002/actp.1982.010330303

Cited by 22 publications

(4 citation statements)

References 13 publications

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“…This, in turn, seemingly demonstrates that aggregates are reactive in their own right, an event for which evidence and suggestions are available. 52,53,[86][87][88][89] Generally, the potential for the existence of aggregation states other than dimers and tetramers has not been considered. A noteworthy exception to this is contained in the 1966 results of Makowski and Lynn.…”

Section: Discussionmentioning

confidence: 99%

Aggregation in Living Polymer Solutions by Light and Neutron Scattering: A Study of Model Ionomers

Fetters¹,

Balsara²,

Huang³

et al. 1995

Macromolecules

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Small angle neutron scattering in combination with dynamic and static light scattering has been used to evaluate the association behavior of the styryl-and dienyllithium head groups in benzene. Both types of lipophobic active centers were found to aggregate as dimers which in turn can self-assemble to yield large scale structures. For the dienyllithium systems no evidence for the presence of tetrameric aggregates was found. The assay of the large scale structures revealed them to be prolate ellipsoids. Thus, these model ionomer systems exhibit diblock copolymer and surfactant style behavior in their capacity to generate cylindrical micelles.

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Section: Discussionmentioning

confidence: 99%

Aggregation in Living Polymer Solutions by Light and Neutron Scattering: A Study of Model Ionomers

Fetters¹,

Balsara²,

Huang³

et al. 1995

Macromolecules

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“…Aggregates are the predominant species in anionic polymerization in nonpolar solvents. It is assumed that propagation occurs predominantly 34,35 or exclusively 36 via nonaggregated species; i.e. aggregated polymers are much less active or even inactive.…”

Section: Scheme 1 Two-state Mechanism With Unimolecularmentioning

confidence: 99%

General Kinetic Analysis and Comparison of Molecular Weight Distributions for Various Mechanisms of Activity Exchange in Living Polymerizations

1997

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The molecular weight distributions in many living (e.g. anionic, group transfer, cationic, and radical) polymerizations strongly depend on the dynamics of various equilibria between chain ends of different reactivity. A very important special case is equilibria between active and dormant centers. Various mechanisms including uni- and bimolecular isomerization (or activation/deactivation), aggregation, and direct bimolecular activity exchange (“degenerative transfer”) are discussed and compared. For all these mechanisms (and for both fast and slow monomer addition), the averages of the molecular weight distribution and the polydispersity index (DPI), P̄ w/P̄ n, are derived in a unified way. Their dependencies on three universal parameters are analyzed: (i) on the reactivity ratio of the two species, λ = k‘p/k*p, (ii) on the fraction of the more active species, α = P*/I 0, which is determined by the initial concentrations of reagents, and (iii) on a generalized exchange rate parameter, β, which quantifies the rate of exchange relative to that of propagation. The dependence of β on the initial concentrations of reagents is defined by the mechanism of exchange and can be used as a mechanistic criterion to distinguish between various possible mechanisms. For the typical case β > 1, the PDI decreases with monomer conversion, which is a common observation in many living polymerizations where 10 ≤ β ≤ 100 was determined. At full conversion, a simple relation, P̄ w/P̄ n ≈ 1 + ϑ/β, is valid, where ϑ depends on α and λ. For the common case where one species is dormant this simplifies further to P̄ w/P̄ n ≈ 1 + 1/β. Generally, the molecular weight distribution is narrower if monomer is added slowly.

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“…Furthermore, the notion of aggregate unreactivity no longer seems tenable. 63,[66][67][68][69][70] This receives support from the observations that freeze-dried SLi and SBdLi readily react 63,71,72 at room temperature with gaseous CO 2 , dienes, and ethylene oxide. The aggregates are directly involved in these reactions since facile dissociation at room temperature is not feasible for vitrified polystyrene chains.…”

Section: Discussionmentioning

confidence: 90%

“…This is in agreement with previous conclusions pertaining to these diene-based systems.The increase in polymer molecular mass and concentration seemingly leads to dimeric aggregates: a finding in accord with the melt 50 and concentrated solution viscosity results 56-58 and the SANS data for an SBdLi(33) chain. , The self-assembling behavior of these headgroups is similar to that observed for surfactant and ionomer systems and is compatible with generic polymer brush behavior 1 . Furthermore, the notion of aggregate unreactivity no longer seems tenable. ,− This receives support from the observations that freeze-dried SLi and SBdLi readily react ,, at room temperature with gaseous CO 2 , dienes, and ethylene oxide. The aggregates are directly involved in these reactions since facile dissociation at room temperature is not feasible for vitrified polystyrene chains.…”

Section: Discussionmentioning

confidence: 96%

Self-Assembling Behavior of Butadienyllithium Headgroups in Benzene via SANS Measurements

Stellbrink¹,

Willner²,

Richter³

et al. 1999

Macromolecules

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The self-assembling behavior of butadienyllithium (−CH2−CHCH−CH2−Li) headgroups in benzene has been studied via the use of small-angle neutron scattering (SANS). The carrier polystyrene chain molecular mass was 2.6K. Previous work has shown that the styryllithium headgroup can simultaneously form aggregated architectures encompassing tetramers and dimers along with a small number, ∼0.1%, of chains engaged in the formation of large scale mass fractal aggregates. That aggregation behavior contradicts the long entrenched belief that the sole self-assembled state of styryllithium headgroups is dimeric. This study shows that the butadienyllithium active centers exhibit more complicated aggregation tendencies than their styryllithium counterparts. For example, the butadienyllithium headgroup can form star-shaped structures with mean functionalities as large as 10 in addition to dimers. This structural versatility is in obvious conflict with the current propagation model that requires tetramers as the solitary aggregation state.

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Influence of the concentration of growing chains on the polymerization rate of butadiene and the microstructure of the polymer formed in the polybutadienyllithium‐butadienealiphatic hydrocarbon system

Cited by 22 publications

References 13 publications

Aggregation in Living Polymer Solutions by Light and Neutron Scattering: A Study of Model Ionomers

Aggregation in Living Polymer Solutions by Light and Neutron Scattering: A Study of Model Ionomers

General Kinetic Analysis and Comparison of Molecular Weight Distributions for Various Mechanisms of Activity Exchange in Living Polymerizations

Self-Assembling Behavior of Butadienyllithium Headgroups in Benzene via SANS Measurements

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