Studies on Dilithium Initiators. 2. The Bimodal Molecular Weight Distribution in Polyisoprene

Bredeweg, C. J.; Gatzke, A. L.; Lo, Grace Y. S.; Tung, L. H.

doi:10.1021/ma00086a037

Cited by 24 publications

(9 citation statements)

References 2 publications

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“…The major problem is that these initiators are usually highly associated in hydrocarbon solvents, leading to the formation of insoluble products, which are not reactive initiators. One of the most effective difunctional initiators, soluble in hydrocarbon media, is the one formed by the addition reaction of sec ‐BuLi with 1,3‐bis(1‐phenyl‐ethenyl)benzene 56–59 …”

Section: Fundamentals Of Anionic Polymerizationmentioning

confidence: 99%

Anionic polymerization: High vacuum techniques

Hadjichristidis

Iatrou

Pispas

et al. 2000

J. Polym. Sci. A Polym. Chem.

544

142

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Anionic polymerization is a powerful tool for the synthesis of a variety of model materials with well‐defined molecular characteristics. However specially designed apparatuses and appropriate high vacuum techniques are needed in order to exclude from the reaction environment all reactive contaminants with the anionic centers. This review describes the basic principles of anionic polymerization as well as detailed experimental methods for the purification of the reagents usually used for the synthesis of model polymeric materials. In addition a few examples of the synthesis of polymers with complex architecture are given. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3211–3234, 2000

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Section: Fundamentals Of Anionic Polymerizationmentioning

confidence: 99%

Anionic polymerization: High vacuum techniques

Hadjichristidis

Iatrou

Pispas

et al. 2000

J. Polym. Sci. A Polym. Chem.

544

142

View full text Add to dashboard Cite

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“…They assumed that the cyclic associates are considerably less reactive than the intermolecular acyclic ones. The authors of the subsequent works [2][3][4][5], in which this phenomenon was investigated in more detail, accepted this explanation too. Madani and colleagues [6] attempted to calculate the fraction of the cyclic associates depending on the length of the "living" bifunctional macromolecules and described the obtained results based on these calculations.…”

Section: Introductionmentioning

confidence: 93%

“…Authors of the works mentioned above [1][2][3][4][5][6] is easy to show that the concentration of the "living" active sites in such gel is huge at the initial stage of polymerization, i.e. for the very short chains.…”

Section: The¯rst Model Of Polymerization In the Two-phase Reaction MImentioning

confidence: 99%

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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“…Over the last 40 years, many attempts have been made to understand the behavior of dilithium initiators in the polymerization of dienes 8–16. In 1969, Fetters and Morton3 used 1,4‐dilithio‐1,1,4,4‐tetraphenylbutane to prepare ABA triblock copolymers (A: α‐mestyrene and B: isoprene) with low vinyl content for the central block.…”

Section: Introductionmentioning

confidence: 99%

“…In 1994, Tung and coworkers studied the development of bimodality in the polymerization of isoprene, in the absence of polar additives, using PEB‐ and MPEB‐based dilithium initiators 23. After a thorough research, they finally attributed the bimodal MW distribution of polyisoprenes to monofunctional initiating species present in the polymerization solution.…”

Section: Introductionmentioning

confidence: 99%

Influence of (1,3‐phenylene)bis(3‐methyl‐1‐phenyl pentylidene)dilithium initiator concentration on the modality of polybutadiene

Vasilakopoulos

Hadjichristidis

2012

J. Polym. Sci. A Polym. Chem.

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The strong influence of (1,3‐phenylene)bis(3‐methyl‐1‐phenyl pentylidene)dilithium initiator (DLI) concentration on the modality of polybutadiene (PBd) in the presence of lithium s‐butoxide (s‐BuOLi) in benzene, at room temperature, has been studied. The quality of DLI has been evaluated by gas chromatography‐mass spectrometry (GC‐MS) and 1H NMR. Keeping s‐BuOLi/C‐Li ratio (R) close to unity, at relatively high DLI concentrations (C > 7 × 10−4 M), monomodal high 1,4‐PBds with polydispersity index less than 1.07 were obtained, whereas bimodal ones at lower concentrations (C < 6 × 10−4 M). The effect of C‐Li concentration on the modality of PBd has been evaluated using size exclusion chromatography on samples taken during and at the end of the polymerization. Viscosity observations have also been used to further support the results. The bimodality of PBd has been attributed to partially terminated difunctional species because of the inevitable presence of protic impurities in the polymerization solution, although high vacuum technique was used, which becomes more significant at low initiator concentrations. Moreover, the strong influence of s‐BuOLi on the microstructure of PBd has been demonstrated by 1H NMR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

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Studies on Dilithium Initiators. 2. The Bimodal Molecular Weight Distribution in Polyisoprene

Cited by 24 publications

References 2 publications

Anionic polymerization: High vacuum techniques

Anionic polymerization: High vacuum techniques

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

Influence of (1,3‐phenylene)bis(3‐methyl‐1‐phenyl pentylidene)dilithium initiator concentration on the modality of polybutadiene

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