Silanol terminated polydimethylsiloxane

A typical condensation system involves the reaction of a silanol-terminated polydimethylsiloxane with a multi-functional organosilicon cross-linking agent such as Si(RO)4 Figure 29.8). Pot life will vary from a few minutes to several hours, depending on the catalysts used and the ambient conditions. Typical catalysts include tin octoate and dibutyl tin dilaurate. 

The synthesis of oligomeric peralkylated polyaminophosphazenes based upon the P3 and P4 templates is an elegant (but complicated), hazardous, and expensive multi-step process. To exploit catalysts of this type in silicone synthesis on an industrial scale would require a much simplified and lower-cost synthetic protocol. One of the simplest and lowest-cost routes to a conjugated -P=N- template that forms the framework for the synthesis of phosphazene base materials is via phosphonitrilic chloride oligomers (Fig. 3). These are well-known acidic catalysts used in the silicone industry for the condensation polymerization of silanol-terminated polydimethylsiloxanes. Catalysts of this type are most commonly prepared by the reaction of PCI5 with NH4CI or HMDZ,... 

The characterization of polysiloxane-modified mesoporous silica gels derived from the acid catalyzed hydrolysis of tetraethoxysilane and oligomeric silanol terminated polydimethylsiloxane using Si CPMAS NMR has been report. ... 

Polydimethylsiloxane, silanol-terminated. See Dimethicone, silanol-terminated Polydimethylsiloxane, trimethylsiloxy-terminated CAS 9016-00-6... 

Silane, vinyl trichloro-. See Vinyltrichlorosilane Silane, vinyl triethoxy. See Vinyltriethoxysilane Silanol-terminated dimethicone Silanol-terminated polydimethylsiloxane. See Dimethicone, silanol-terminated Silanol-terminated... 

GE foul release coatings are comprised of a silicone topcoat and a silicone oil additive, typically at 10 or 20 weight percent. The silicone topcoat, RTVll (GE Silicones) is a room temperature condensation moisture cure system, which contains a silanol terminated polydimethylsiloxane (PDMS), CaCOj filler, tetraethoxy-orthosilicate (TEOS) crosslinker and dibutyltin dilaurate, a Sn(IV) catalyst. The chemistry of this system is shown below in Figure 1. 

An interesting variation of an ammonium silanolate catalyst was described by Hoffman and Leir40. They prepared tetramethylammonium 3-aminopropyldimethylsilanolate and used it to synthesize 3-aminopropyl terminated Polydimethylsiloxane (PDMS). 

Elastomers and nonsilanol terminated fluids are produced by base-catalyzed polymerization of low-molecular weight siloxanes. Polydimethylsiloxanes are also produced by ring opening polymerization of D3, D4, and D5. In the presence of MM or MDDM (endcapper), silicones MD M are formed otherwise, silanol terminated polysiloxanes may be obtained. 

Many modifications of polydimethylsiloxanes have been made in response to the needs of textiles or of the fabric care industry. Amide-fimctional, amine-functional silicones, and PDMS are key ingredients of fabric softeners and can confer properties such as conditioning, antiwrinkling, ease of ironing, softness, and water absorbency. PDMS and silanol-terminated PDMS confer... 

Low molecular weight, hydroxy-terminated polydimethylsiloxanes may be prepared by hydrolyzing dimethyldichlorosilane in the presence of small quantities of a base, e.g., calcium carbonate. The base is added continuously and neutralizes the hydrochloric acid formed and thus protects the silanol groups from further condensation. 

The thickness profiles of microdroplets of polydimethylsiloxane (PDMS) oligomers deposited on oxidized silicon wafers exhibit equal thickness steps, each 0.7 nm thick (Fig. 5.4). The number of visible steps, their lengths, and their growth d3mamics depend on the surface chemistry of the wafers. The common step thickness is the transverse size of the PDMS chain, which means that each step corresponds to a compact flat monolayer of chains, that is, a 2D nonvolatile liquid. Information on the disjoining pressure, and on the friction coefficients between successive layers, can be extracted. " The d3mamics of adsorption of silanol ends when silanol-terminated PDMS (PDMS-OH) is deposited on the wafer can also be monitored in real time. ... 

Silanol-terminated linear polydimethylsiloxane pol3miers can be crosslinked to elastomers by a variety of reactions. Among these is the reaction with acetoxysilanes, shown schematically in reaction sequence A. The first reaction takes place upon... 

After separation and purification by distillation, the difimctional compound dimethyl di-chlorosilane is then allowed to react with water tQ form a hydrolyzate, which is a mixture of cyclic and linear polydimethylsiloxanes. The linear components are low-molecular weight hydroxyl (silanol) terminated polymers. 

The mesh stracture responsible for elasticity is achieved by the condensation of a mixture of silicone prepolymers on the fabric surface. This mixture may often consist of a terminal silanol (a, co-dihydroxy polydimethylsiloxane), methyl hydrogen silane and a metal salt catalyst (Fig. 12.1). The crosslinking reaction that forms the elastic structure in shown in Fig. 12.2. Some hydrosilane groups can be oxidised by air to silanol groups. Condensation of the silanol groups of neighbouring molecules generates crosslinked structures that are necessary for elasticity. 

Silicone Room Temperature Vulcanizing Gross-Linking. Condensation-cured polydimethylsiloxanes contain terminal silanol groups which condense with the silanols produced by ambient moisture hydrolysis of acyloxysilanes. Methyltriacetoxysilane, ethyltriacetoxysilane, and tetraacetoxysilane are the most commonly used cross-linking agents. 

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