Ring-opening polymerization cyclosiloxane

Chojnowski, J. Ring-Opening Polymerization of Cyclosiloxanes. In Gelest Catalog Arkles, B., Larson, G., Eds. Gelest Inc. Morrisville, PA, 2004, pp 389-105. 

Boileau and coworkers11 have used a novel trimethylsilylmethyl lithium initiator MesSiCTDLi (1), in combination with a cryptand [211], for the ring-opening polymerization of cyclosiloxanes. Initiation of hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4) polymerization has been followed by H, 7Li, 13C and 29Si NMR. 

Sormani PM, McGrath JE (1985) Kinetics and mechanisms of the anionic ring opening polymerization of cyclosiloxanes in the presence of bis(l,3-aminopropyl tetramethyl-disiloxane) In McGrath JE (ed) Ring opening polymerization kinetics mechanisms and synthesis. ACS Symposium Series No 286... 

The reactions of vinylcyclosiloxanes and vinylcyclosilazanes with styrene in the presence of RuHCl(CO)(PCy3)2 opened a new route to functionalized monomers for the ring-opening polymerization of cyclosiloxanes and cyclo-silazanes (Eq. 29) [56]. 

The consumption of cyclosiloxane during polymerization and copolymerization was monitored by GC. The conversion of D3 was nearly 100 % (Fig. 1). In contrast, the ring-opening polymerization of d/ yielded a conversion of about 60 % only (Fig. 2). During the copolymerization with D3 the cyclic vinylsiloxanes showed a similar behavior as observed during homopolymerization. 

If desired, the linear oligosiloxanes, and indeed any linear polydimethylsiloxane, can be converted into cyclosiloxanes by base-catalyzed pyrolysis. If this reaction is carried out under equilibrating conditions and the products are fractionally distilled with removal only of the most volatile compound, D3, the entire mixture can be converted to this valuable intermediate. This procedure is frequently used to obtain pure D3 and D4, useful for polymer synthesis by ring-opening polymerization. 

List II. Typical Cyclosiloxane Monomers Used in Ring-Opening Polymerization ... 

Rates of reaction (Rp) in ring opening polymerizations initiated by alkali metals are typically proportional to a fractional order of the initiator and close to first order in cyclosiloxane ... 

Mechanism of Equilibration. The generally accepted mechanism for the base-catalyzed ring-opening polymerization of cyclosiloxanes involves attack of the basic catalyst at the silicon atom (15). It has been proposed, and generally accepted, that the active species is a partially dissociated siloxanolate anion (13). In the results presented in this chapter, significant differences in reaction rates were observed as the corresponding cation of the siloxanolate species was varied. The more rapid disappearance of D4 and aminopropyldisiloxane in the presence of these catalysts increased in the following order ... 

Acheson process, 566 Acid-initiated ring-opening polymerization comparison widi base-initiated process, 79 kinetics, 79-80 mechanism, 79-81 rate retardation by water, 81 relative reactivities of cyclosiloxanes, 79 step-growth process, 79 Acyclic oligosilanes, photochemical transformations, 432/-433/ Acylsilanes... 

Keywords cyclosiloxanes, ring-opening polymerization, silyloxonium ions... 

The structure of the active propagation center in the cationic ring-opening polymerization (ROP) of cyclosiloxanes is still controversial. Trisilyloxonium ions generated from hexamethyl-cyclotrisiloxane, D3, and octamethylcyclotetrasiloxane, D4, were observed at low temperature by Olah et al. [I] and their participation as intermediates in cationic ROP of cyclosiloxanes was postulated. However, the main objection against this mechanistic concept is a relatively low rate of polymerization when an initiator able to form persistent tertiary oxonium ions is used [2]. 

Summary Phosfdiazene bases represent a new class of highly active non-ionic catalysts that rapidly polymerize cyclosiloxanes with equilibrium attained in very short reaction times at very low catalyst levels. To date, phosphazene base catalysts have been considered an academic curiosity because of the complicated and hazardous synthetic protocol used to prepare them. A facile synthetic process has been developed, which yields ionic phosphazene bases in three steps with an overall yield of qrproximately 75%. This is achieved through nucleophilic substitution of ionic phosphonitrilic chloride oligomers with secondary amines, followed by anion exchange. These ionic phosphazenes were found to exhibit similar reactivity in the ring-opening polymerization of cyclosiloxanes to that of the non-ionic phosphazene base. 

Summary PDMS-6-PEO short-chain diblock copolymers were prepared via anionic ring-opening polymerization of cyclosiloxanes. Applying this method, various well-defined block copolymers with different compositions were synthesized and their phase behavior was investigated. The polymers predominantly showed lamellar phases in aqueous solutions. At small surfactant concentrations, vesicles were formed, as observed via cryogenic TEM. The aggregates of the diblock copolymers were used for the formation of lamellar thin films, applying the evaporation-induced self-assembly approach. 

Cyclosiloxanes, cationic ring-opening polymerization of 85MI16. Cyclosiloxanes, structures of 80UK518. 

Organocatalytic ring-opening polymerization involving lactones, morpholine-2,6-diones, cyclosiloxanes, and oxadisilacyclohexanes as monomers and/or heterocyclic carbenes as catalysts 07CRV5813. 

Organocatalytic ring-opening polymerization of oxadisilacyclohexanes and cyclosiloxanes 07CRV5813. 

Polysiloxanes are a well-established type of polymers with widespread technical applications. One way to obtain such compounds is ring-opening polymerization (ROP) of highly strained cyclosiloxanes [1]. 

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