Reactions of organolithium reagents with siloxane substrates

Frye, Cecil L.; Salinger, Rudolf M.; Fearon, F. W. G.; Klosowski, Jerome M.; Deyoung, T.

doi:10.1021/jo00830a012

Cited by 97 publications

(55 citation statements)

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“…For the n-butyllithium system, k 1 and k 2 (Scheme 2) are very fast [10]. This is corroborated by the data in Figures 3, 4, and 5 since both the n-2p and n-3p track parallel to one another and they are very small relative to n-1p.…”

Section: Resultssupporting

confidence: 66%

“…This difference is believed to be the result of steric hinderence. Efficient nucleophilic attack of the tri-siloxanolate by unreacted organolithium species (Scheme 2) favors the n-butyllithium [10] opposed to the more sterically hindered sec-butyllithium. The ␣-substituted sec-butyllithium slows the rate of s-3 cleavage and facilitates more time for D 3 ring-cleavage.…”

Section: Resultsmentioning

confidence: 99%

“…Frye et al [10] studied the reactions between several organolithium reagents and a series of siloxane monomers in an attempt to identify the lithium siloxanolate initiator species. The gel permeation chromatography results showed that n-butyllithium reacted with D 3 to form three lithium siloxanolate species that are shown in Scheme 2.…”

Section: Inear Polydimethylsiloxane (Pdms) Is Primarilymentioning

confidence: 99%

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Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D₃)

Hawkridge

Gardella

2003

J. Am. Soc. Mass Spectrom.

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Matrix assisted laser desorption ionization (MALDI) was used to study the organolithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D 3 ) in a mixed solvent system. The mass spectral peak intensities were monitored to determine the effects of polymerization time, initiator concentration, and reaction temperature on the formation of the mono, di, and trisiloxanolate initiator species and the extent of chain redistribution. The three initiator species were formed by reacting n-butyllithium and sec-butyllithium with D 3 in nonpolar solvent. The mass spectral results showed that sec-butyllithium and n-butyllithium form different populations of initiator species under the same conditions and that the measured mass spectral peak intensities do not accurately represent the population of siloxanolate initiator species prior to propagation. The changes in peak intensities were attributed to chain redistribution. . The molecular weight and product purity in these systems are difficult to control because both methods are susceptible to side reactions that broaden the polydispersity (M w /M n ). The most common side reactions are chain redistribution and cyclization shown in Scheme 1. Chain redistribution occurs when a propagating chain reacts with another chain to remove a segment of polymer without terminating the reaction. Cyclization occurs when a propagating chain reacts with itself to form cyclic species (D 3 , D 4 , D 5 , etc.). This type of side reaction is commonly referred to as chain backbiting. Lee et al. [3] first reported a new method for producing narrow molecular weight PDMS that was free of cyclic impurities. It was shown that n-butyllithium opened the D 3 ring in nonpolar solvents to form lithium siloxanolate initiators but did not propagate without the addition of a small amount (1-3%) of base promoting solvent (in this case these include polar aprotic solvents such as DMSO and THF). The control of the initiator basicity coupled with the high reactivity of the D 3 monomer significantly reduced chain redistribution and eliminated the formation of cyclic impurities.The reaction between organolithium initiators and D 3 is not well understood due in large part to the unique behavior of the initiators and the lithium counterions in solution. Organolithium compounds associate in nonpolar solvents to form aggregated species of various degrees due to the electron deficient nature of the lithium atom [4]. N-butyllithium, for example, forms a hexameric aggregate [5] whereas sec-butyllithium forms a tetrameric aggregate [6] in hydrocarbon solvents. Studies involving the reaction of organolithium species with styrene [7,8] and dienes [8,9] have shown that the degree of association directly affects the reactivity. The less associated organolithium species are found to be generally more reactive. Upon reacting with D 3 , it has been proposed that the lithium counter ions associate to form lithium siloxanolate aggregates. The degree to which these proposed structures are associated and the mech...

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Section: Resultssupporting

confidence: 66%

Section: Resultsmentioning

confidence: 99%

Section: Inear Polydimethylsiloxane (Pdms) Is Primarilymentioning

confidence: 99%

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Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D₃)

Hawkridge

Gardella

2003

J. Am. Soc. Mass Spectrom.

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“…The initiator lithium sec-butyldimethylsilanolate (sec-BuSi(Me 2 )OLi) was prepared by reacting sec-BuLi (Aldrich, 1.3 mol/L in cyclohexane) with 1/3 equivalent hexamethylcyclotrisiloxane (Aldrich, ú 98%, distilled from CaH 2 ). 8 Chlorotrimethylsilane (ABCR, 99.9%) was used as received. …”

Section: Methodsmentioning

confidence: 99%

Poly[(S)-(+)-2-methylbutyl]pentylsiloxane

Molenberg

Michalke

Möller

et al. 1998

J. Polym. Sci. A Polym. Chem.

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Poly[(S)‐(+)‐2‐methylbutyl]pentylsiloxane has been synthesized by anionic ring opening polymerization of the corresponding strained cyclic trisiloxane \documentclass{article}\pagestyle{empty}\begin{document}$ (D^{\rm{MeBu, Pe}}_{3}) $\end{document} with cryptated lithium (Li+/[211]) as counterion. The polymer did not show the low and high temperature crystalline phases, that are generally found for poly(di‐n‐alkylsiloxane)s. Instead, the material formed a hexagonal columnar mesophase until it melted around 400°C. MAS and solution 13C‐ and 29Si‐NMR, polarizing microscopy and WAXS indicated an unexpectedly regular chain structure. It was tentatively concluded that the steric interaction of the (S)‐(+)‐2‐methylbutyl side chains introduces sufficient regularity of the tacticity and that the chains tend to adopt a defect helix conformation. On the other hand, DSC showed the presence of a glass transition at −113°C, indicating a high flexibility of the backbone. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 169–177, 1998

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“…These side reactions can be either with siloxane bond along the chain, or, much faster, with siloxane bonds in the vicinity of the siloxanolate group [8]. At this point, the reaction does loose some of its simplistic appearance and this is why the model system had to be carefully chosen for the initial mechanistic studies of anionic polymerization to eliminate the effect of the side reactions.…”

Section: D4 -Polymer + Dnmentioning

confidence: 99%

Anionic Polymerization of Siloxanes Non-Trivial Model System for Studies of Common Phenomena

Mazurek

1987

Recent Advances in Anionic Polymerization

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Reactions of organolithium reagents with siloxane substrates

Cited by 97 publications

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Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D₃)

Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D₃)

Poly[(S)-(+)-2-methylbutyl]pentylsiloxane

Anionic Polymerization of Siloxanes Non-Trivial Model System for Studies of Common Phenomena

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Reactions of organolithium reagents with siloxane substrates

Cited by 97 publications

References 0 publications

Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D3)

Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D3)

Poly[(S)-(+)-2-methylbutyl]pentylsiloxane

Anionic Polymerization of Siloxanes Non-Trivial Model System for Studies of Common Phenomena

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Product

Resources

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Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D₃)

Evaluation of matrix-assisted laser desorption ionization mass spectrometry for studying the sec-butyllithium and n-butyllithium initiated ring-opening polymerization of hexamethylcyclotrisiloxane (D₃)