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

Fetters, L. J.; Balsara, NP; Huang, J. S.; Jeon, Hs S.; Almdal, Kristoffer; Lin, MY

doi:10.1021/ma00118a031

Cited by 58 publications

(106 citation statements)

References 32 publications

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“…In addition, the strong increase of the LS intensity of the living chains in the low-q regime (q < 0:01 nm À1 ) demonstrates the existence of a small amount of large aggregates, as well known for living chains in nonpolar solvents. [8][9][10][16][17][18] These large aggregates should have existed in all living PB solutions examined.…”

Section: Scattering Datamentioning

confidence: 94%

“…These small aggregates coexist with a minor amount of large aggregates with f > 100, as revealed from light/neutron scattering experiments. [8][9][10][16][17][18] Recently, the neutron scattering and 1 H NMR studies were conducted during the polymerization process of PBLi in heptane to reveal an interesting decrease of f with increasing conversion (from f of the order of 100 to f ¼ $ 4 for the main component of the aggregates). This decrease was intimately related to the NMR-determined initiation/polymerization rates.…”

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confidence: 99%

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Dynamics of Monofunctional Polybutadienyl Lithium Chains Aggregated in Benzene

Oishi

Watanabe

Kanaya

et al. 2006

Polym J

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ABSTRACT:Viscosity, 7 Li-NMR, and neutron/light scattering measurements were conducted for living monoanionic polybutadienyl lithium chains of various molecular weights M and concentrations C. In benzene, the living chains aggregated with each other at their Li ends to form star-like tertramers as the major component, as confirmed from the viscosity and scattering measurements. An average time ( dif required for the tetrameric aggregate to diffuse over a distance to a neighboring aggregate was estimated from the viscosity data with the aid of the bead-spring model (valid at the small C and M examined). This ( dif , of the order of 10 À5 -10 À7 s, was much smaller than the Li-Li exchange time ( ex determined from the 7 Li-NMR measurement. The large difference between ( dif and ( ex indicates that the dissociation of the aggregates, occurring through the Li-Li exchange, is much less frequent than the thermal collision of the aggregates. The M, C, and T dependencies of the exchange time (dissociation time) ( ex were satisfactorily described by an empirical equation, ( ex / Q os ( dif expðÁE=RTÞ where R and T were the gas constant and absolute temperature, respectively, and Q os denoted an osmotic barrier for mutual approach of the aggregates carrying the aggregated Li species at the center. The activation energy ÁE (¼ $ 88 kJ/mol) was considerably smaller than the bare energy required for breaking the Li-Li bonds and releasing isolated Li species. These results suggest that the collision of the aggregates (under the osmotic barrier) is required for the dissociation of the aggregates and the dissociation results from a cooperative exchange of Li species occurring through formation of a larger, transient aggregate.

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Section: Scattering Datamentioning

confidence: 94%

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confidence: 99%

Dynamics of Monofunctional Polybutadienyl Lithium Chains Aggregated in Benzene

Oishi

Watanabe

Kanaya

et al. 2006

Polym J

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“…Really, Stellbrink et al [27] exhibited both the dimeric, and the tetramerous associates at studying of the benzene solutions of polystyryl lithium having MW 2600 by the method of small angle neutron scattering. At the same time, Fetters et al [28] exhibited only the dimeric associates by the same method in the solutions of polystyryl lithium having MW about 8600 and 15000.…”

Section: Resultsmentioning

confidence: 91%

Bimodality of molecular mass distribution of polydienes obtained under the action of dilithium initiators in hydrocarbon media: the reasons, mathematical simulations, and their experimental testing

Estrin

2004

Open Chemistry

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Bimodal molecular mass distribution (MWD) of polymers, obtained upon polymerization of hydrocarbon monomers in the nonpolar media under the action of dilithium initiators, is the consequence of separation of the reaction mixture into two phases. Bifunctional /living/ oligomers produce the insoluble sediment due to tetrameric association of the lithium active sites (the swollen gel-fraction). Part of the active site remains in the solution (the solfraction). Di¬erence in the concentrations of the active sites into the phases leads to di¬erence between the propagation rates of the /living/ chains and, as a result, to Bimodal MWD. The mathematical model of polymerization in the two-phase system is proposed. Satisfactory agreement between the calculations and the experiments is shown for butadiene polymerization in heptane under the action of 1,4-dilithiumpentane. Regulation of MWD up to the complete elimination of bimodality is possible via the programmed dosage of monomer and solvent into the reactor.

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“…4,11,15,16 The aggregation occurs not only for the initiators but also for the polymerized anionic chains in nonpolar solvents. Scattering/viscosity experiments revealed that the anionic chains form aggregates with the main aggregation number f being determined by the chemistry of the anionic ends: [1][2][3][4]7,12,[16][17][18][19][20][21][22] For example f ¼ 2 for polystyrenyl lithium chains in the range of the molecular weight 10 < 10 À3 M < 200. The aggregation number has a distribution (for example, ranging mainly from 3 to 5 for polybutadienyl lithium in cyclohexane) 21 and a trace amount of huge aggregates (with the aggregation number !…”

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confidence: 99%

Kinetics of Living Anionic Polymerization of Polystyrenyl Lithium in Cyclohexane

Mishima

Yamago

Watanabe

2008

Polym J

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Living anionic polymer chains polymerized with organolithium initiators usually form aggregates through their Li ends in nonpolar solvents. This aggregation structure strongly affects the anionic polymerization (propagation) kinetics. In the conventional molecular picture, the aggregates are assumed to be chemically inert and the propagation occurs only though the dissociated unimers, which leads to single-exponential decay of the residual monomer fraction ðtÞ with time t. This picture was tested by 1 H NMR measurements for protonated polystyrenyl lithium (hPSLi) polymerized in a nonpolar solvent, deuterated cyclohexane (dCH). The measurements were made mostly at 34.5 C, the theta condition for neutral (non-anionic) high-M hPS. An oligomeric, deuterated styrenyl lithium (oSLi) was utilized as an initiator so that the NMR data exclusively detected the propagation kinetics (no contamination of the initiation process). For hPSLi with the molecular weight ranging from 4:2 Â 10 3 to 276 Â 10 3 , ðtÞ was found to exhibit almost single-exponential decay at short t (where ðtÞ > 10{20%) but the decay slowed at longer t (for smaller ðtÞ). Furthermore, ðtÞ decayed more slowly when the polymerization batch contained neutral, deuterated dPS (not affecting the hPSLi chemistry) at a concentration in the semi-dilute regime. These results indicated the failure of the conventional molecular picture assuming the chemical inertness of the aggregates. Consequently, some (unstable) aggregates appeared to contribute to the propagation, and the osmotic interaction among the aggregates as well as with the coexisting dPS seemed to reduce this contribution at long t thereby giving the non-singleexponential decay of ðtÞ. A simple kinetic model considering this osmotic effect consistently described the behavior of ðtÞ in the absence/presence of dPS for the polymerization of hPS in a range of 10 À3 M ¼ 11{73, although deviations were noted for the polymerization of lower-and higher-M hPS.

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

Cited by 58 publications

References 32 publications

Dynamics of Monofunctional Polybutadienyl Lithium Chains Aggregated in Benzene

Dynamics of Monofunctional Polybutadienyl Lithium Chains Aggregated in Benzene

Bimodality of molecular mass distribution of polydienes obtained under the action of dilithium initiators in hydrocarbon media: the reasons, mathematical simulations, and their experimental testing

Kinetics of Living Anionic Polymerization of Polystyrenyl Lithium in Cyclohexane

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