Transient catalysts for the polymerization of organosiloxanes

Gilbert, Alfred R.; Kantor, Simon W.

doi:10.1002/pol.1959.1204013603

Cited by 99 publications

(70 citation statements)

References 12 publications

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“…To some extent, in polymerization with complex counter-ions (tetramethylammonium silanolate, tetrabutylphosphonium silanolate [30]), advantage can also be taken of the differences in the' reactivity of D3 and linear or cyclic strainless siloxane molecules, since these bulky counter-ions are not able to be effectively solvated by polydimethylsiloxane molecules. These catalytic systems, lithium silanolates in particular, have very important practical applications, as they permit the synthesis of polydimethylsiloxane polymers and block copolymers, e.g.…”

Section: Kinetically Controlled Polymerizationmentioning

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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Section: Kinetically Controlled Polymerizationmentioning

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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“…Thus, the usual need for catalyst neutralization and removal following polymerization is eliminated. They are often termed "transient" catalysts (34). They found that the rate of copolymer formation, the viscosity of the resulting copolymers, and the equilibrium yield of linear species all decreased regularly as the mole percent of phenyl tetramer was increased in the reaction mixture.…”

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

confidence: 99%

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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“…This time is believed sufficient to decompose the so-called transient catalyst (13) and thus inactivate the equilibration process.…”

Section: Equilibration Polymerization Of Epoxy Functional Disiloxanesmentioning

confidence: 99%

Elastomeric Polysiloxane Modifiers for Epoxy Networks

Riffle¹,

Yilgör

Tran

et al. 1983

ACS Symposium Series

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Novel elastomeric polysiloxane modifiers for epoxy networks have been synthesized and characterized. In addition, curing studies of conventional epoxy resins incorporating these oligo mers have been conducted. Structures were prepared having either epoxide, primary amine and/or secondary amine endgroups. The polymerization step for the siloxanes consisted of a base cata lyzed equilibration of the appropriately functionalized disiloxane and octamethylcyclotetrasiloxane. In the case of hydroxy piperazine terminated modifiers, polymers were first synthesized with epoxy endgroups. These endgroups were then subsequently capped with an excess of piperazine prior to curing. The oligomers were characterized by FTIR, 'H and 13C NMR, GPC, endgroup analysis and vapor pressure osmometry. The secondary amine terminated oligomers basically act as linear modifiers. By contrast, the aminopropyl functional siloxanes produce a crosslinked network. Piperazine terminated oligomers show much better compatibility with the epoxy resins compared to the aminopropyl terminated oligomers. This is especially true if the modifier contains an amide group. The curing reactions of the epoxy resins (EPON resin-828) using these oligomers and a cycloaliphatic diamine (PACM-20) were followed under a variety of conditions by DSC. Percent conversion versus time plots showed that reactivities of the functional siloxanes are higher than the cycloaliphatic amine at comparable temperatures. X-ray photoelectron spectroscopy shows the surfaces of the polysiloxane modified materials to be predominantly siloxane even at quite low bulk levels of the reactive oligomers. Preliminary mechanical property studies are encouraging and detailed morphology-property studies are continuing.

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Transient catalysts for the polymerization of organosiloxanes

Cited by 99 publications

References 12 publications

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

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

An Overview of the Polymerization of Cyclosiloxanes

Elastomeric Polysiloxane Modifiers for Epoxy Networks

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