Kinetics of the Polymerization of a Cyclic Dimethylsiloxane<sup>1</sup>

Grubb, W. T.; Osthoff, Robert C.

doi:10.1021/ja01611a003

Cited by 124 publications

(29 citation statements)

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“…They result from the hydrolytic polycondensation of dimethyl dichlorosilane or from the equilibration of poly(dimethyl siloxane)s. D 3 is the thermodynamically least stable and most reactive cyclosiloxane, and detailed studies of its cationic polymerization were published. [1][2][3] Numerous studies deal with the acidic [4][5][6][7][8][9][10][11][12][13][14] or basic equilibration [15][16][17][18][19][20][21][22][23][24][25] of D 4 . Concentrated sulfuric acid and triflic acid were the most widely used acidic catalysts but SbCl 5 [4] or the combination of FeCl 3 and HCl [12] were also applied.…”

Section: Introductionmentioning

confidence: 99%

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

Yashiro

Kricheldorf

Schwarz

2010

Macro Chemistry & Physics

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Hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5) were equilibrated with potassium tert‐butoxide or triflic acid in bulk at 100 °C to elaborate the 1H NMR and 13C NMR spectra, SEC elution curve, and MALDI‐TOF (MT) mass spectrum of a fully equilibrated poly(dimethylsiloxane). Surprisingly, triflic acid did not effect complete equilibration (even after 360 h), seemingly because cleavage of Si–C bonds eliminates the acidic proton. Large amounts of D4 and D5 together with small amount of D6 were formed in the early stage of the polymerization in contrast to potassium alkoxide‐catalyzed polymerizations. The usefulness of numerous metal triflates as polymerization catalysts of D3 was explored, and only the most acidic ones were active. Bismuth and hafnium triflate catalyzed a polymerization mechanism similar to that of triflic acid but were more active despite their poor solubility. BiCl3 and HfCl4 were considerably less reactive and the polymerization kinetics were quite different from those of the metal triflate catalyzed polymerizations. The decisive role of acidic protons was revealed by addition of a proton scavenger. Bismuth triflate proved to be an interesting and useful catalyst because it combines the highest activity with poor solubility and low toxicity.magnified image

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Section: Introductionmentioning

confidence: 99%

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

Yashiro

Kricheldorf

Schwarz

2010

Macro Chemistry & Physics

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“…A principal area of interest was the effect of catalyst type and concentration on the rate at which aminopropyl-terminated polysiloxane oligomers of well-defined end groups and controlled molecular weight are formed. Previous workers in this area have focused on the reaction kinetics either in the absence of an end blocker (13) or in the presence of a nonfunctionalized end blocker such as hexamethydisiloxane (12). The reaction scheme for the preparation of aminopropyl-terminated difunctionalized oligomers is illustrated in Scheme II.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Fractionation Studies of Functionalized Organosiloxanes

Elsbernd

Spinu

Krukonis

et al. 1989

Advances in Chemistry

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The synthesis of difunctionalized aminopropyl-terminated poly-(dimethylsiloxane) via equilibrium polymerization of the cyclic tetramer in the presence of the functionalized disiloxane was demonstrated. The use of tetramethylammonium and tetrabutylphosphonium siloxanolate anionic catalysts for these reactions was studied. The reactions of the tetramethylammonium and tetrabutylphosphonium catalysts were limited to ~80 °C because of the known transience of these species at higher temperatures. The disappearance of the cyclic tetramer and disiloxane was monitored by HPLC (high-pressure liquid chromatographic) and GC (gas chromatographic) techniques, which indicated that the tetramethylammonium and tetrabutylphosphonium catalysts were much more efficient than the potassium catalyst, even when the potassium catalyst was used at much higher (e.g., 160 °C) temperatures. This behavior may be related to the higher degree of dissociation and, possibly, the enhanced solubility of the tetramethylammonium and tetrabutylphosphonium catalysts relative to the much more studied potassium catalyst. The number-average molecular weight was independent of the catalyst concentration and was influenced only by conversion and the molar ratio of the tetramer to the disiloxane. GPC (gel permeation chromatographic) characterization was also possible by derivatizing 1 Current address: 3M Center, St. Paul, MN 55144 2

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“…At equal molar concentrations, the rates using the hydroxide or siloxanolate of the same metal have been found to be similar (30).…”

Section: S and Stockmayer's Equation For Cyclization Equilibrium Consmentioning

confidence: 88%

An Overview of the Polymerization of Cyclosiloxanes

McGrath

Riffle

Banthia

et al. 1983

ACS Symposium Series

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A review of the polymerization of cycloorgano siloxanes is provided. Cycloorganosiloxanes such as octamethyl cyclotetrasiloxane are the principal intermediate for the formation of high molecular weight polyorganosiloxane polymers. The ring open ing reaction can be initiated through the use of suitable basic or acidic catalysts. The transforma tion of the cyclosiloxanes into linear chains is an equilibrium process characterized by a very low heat of polymerization. At equilibrium conversions one produces 12-15% of cyclic oligomers, which are pre dominantly but not exclusively the cyclic tetramer. Equations from the literature which define these equilibrium are reviewed. The principal mechanisms involved in the anionic ring opening polymerization via initiators such as potassium hydroxide are discussed. A host of other related initiator types have also been used, including the so-called transient catalysts which are based upon quaternary silanolates. The transient catalysts are so described since they rapidly decompose above 130°C to yield inactive byproducts. The anionic polymeri zation of siloxanes is relatively well understood and currently accepted mechanisms are presented. Cationic polymerization of organosiloxanes is also well known but is much less understood. In general, molecular weight vs. conversion curves for the two processes are considerably different and these as pects are reviewed. Molecular weight is often con trolled by disiloxane or low molecular weight siloxane molecules terminated with triorganosiloxy groups. These materials (which are known as end blockers) control the molecular weight due to the 0097-6156/83/0212-0145$08.00/0

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Kinetics of the Polymerization of a Cyclic Dimethylsiloxane¹

Cited by 124 publications

References 4 publications

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

Synthesis and Fractionation Studies of Functionalized Organosiloxanes

An Overview of the Polymerization of Cyclosiloxanes

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Kinetics of the Polymerization of a Cyclic Dimethylsiloxane1

Cited by 124 publications

References 4 publications

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

Synthesis and Fractionation Studies of Functionalized Organosiloxanes

An Overview of the Polymerization of Cyclosiloxanes

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Kinetics of the Polymerization of a Cyclic Dimethylsiloxane¹