Octamethyl cyclotetrasiloxane

The a,oo-difunctional PDMS is obtained by cationic polymerization of octamethyl-cyclotetrasiloxane (D4) in the presence of a known amount of tetramethyldisiloxane, acting as a functional transfer agent. Hydrosilylation reaction is carried out in toluene solution at 90 °C with a platinum catalyst. 

Silica is also deposited by the decomposition of diacetoxy-ditertiarybutoxy silane (DADBS) at 450-550°C and low pressure (< 1 Torr) and by the decomposition of octamethyl-cyclotetrasiloxane in ozone at 400°C at low pressure.P ]P 1... 

Figure 12.14 Pyrogram of the silicone coating from Mello s Tavolo erba. Peak assignments I, hexamethyi cyclotrisiloxane 2, octamethyl cyclotetrasiloxane 3, decamethyl cyiclopenta siloxane 4, dodecamethyl cyclohexasiloxane 5, tetradecamethyl cyclooctasiloxane...

Hazardous Ingredients Octamethyl cyclotetrasiloxane (1 -5%) Hazardous Decomp. Prods. Thermal decomp. COx, traces of incompletely burned carbon compds., SiOs, formaldehyde... 

Chem. Descrip. Reactive silicone resin (36%) in water and octamethyl-cyclotetrasiloxane (15%)... 

The van der Waals bonds between monomer molecules are replaced by covalent bonds between the monomeric units in polymerization. Since van der Waals bond lengths are about 0.3-0.5 nm and covalent bond lengths are, in contrast, about 0.14-0.19 nm, a general contraction occurs. The contraction increases with decreasing monomer molecule size, since more van der Waals bonds per unit mass must be eliminated. Thus, ethylene contracts by about 66%, vinyl chloride by about 34%, styrene by about 14%, and W-vinyl carbazole by as little as about 7.5%. Polymerization of ethylene oxide leads to a volume contraction of 23%, of tetrahydrofuran to one of about 10%, but that of octamethyl cyclotetrasiloxane, however, to a contraction of only 2%. Some strained bicyclic ring systems even polymerize with an expansion. With polycondensation, the volume contraction is smaller with decreasing size of eliminated residue. Polycondensation of hexamethylene diamine with adipic acid leads to a contraction of 22% (water elimination), that of hexamethylene diamine and dioctyl phthalate, on the other hand, to one of 66% (elimination of octanol). 

Figure 16 4. Experimentally obtained equilibrium constants Kcof cyclization as a function of the number N of ring atoms for bulk polyreactions of cyclooctene (PCO) at 25° C, terephthalic acid and ethylene glycol (PET) at 270 C, and octamethyl cyclotetrasiloxane (PDMS) at 110° C. The dotted lines give the theoretically calculated dependence according to Equation (16-49), with the slope —5/2.

Tfie results demonstrated that cyclohexane in the nanoscale slit space between the carbonaceous solids freezes when the distance comes down to 4 nm, even at 8.4 C, which is above the bulk freezing point of 6.4°C. Measurements with octamethyl-cyclotetrasiloxane, bulk freezing point being 18°C, also detected the freezing behavior at an elevated temperature of 22°C. The detected elevation of a few d ee C mi t be felt as a matter of less significance, but we believe that the finding of the definite existence of the elevation would be of much importance in the research field of the phase behavior in nanospaces. 

Pure dichlorsilanes or their precursors, such as the cyclic tetramer, octamethyl cyclotetrasiloxane, are required in order to produce the high molecular weight gums (c. 0-5 x 10 ) which are usually needed. Where the tetramer is used it is equilibrated with a trace of alkaline catalyst for several hours at 150-200 C in order to provide the necessary rearrangement to high molecular weight polymer. 

REACTION OF BENZOVL PEROXIDE WITH OCTAMETHYL-CYCLOTETRASILOXANE... 

Linear polysiloxane can be synthesized by both anionic and cationic polymerizations of cyclic siloxanes such as hexamethylcyclotrisiloxane (n = 3) and octamethyl cyclotetrasiloxane (n = 4). Anionic polymerization is initiated by hydroxide, alkoxides, phenolates, silanolates and siloxoano-lates. The active species in the polymerization is the silanolate anion. Cationic polymerization is initiated by strong protonic acids such as sulfuric acid, trifluoromethane sulfonic acid and trifluoro-acetic acid (equation 53). Both the anionic and the cationic species undergo backbiting reactions during polymerization, such that an equilibrium exists between linear chains and rings. ... 

An important group of polysiloxanes that is used in the medical, pharmaceutical and cosmetic industries are polydimethylsiloxanes (PDMS). Polydimethylsiloxane molecules consist of two functional groups [R Si-Oj, where R represents a methyl group. Polydimethylsiloxanes used in those fields are either linear (methyl silicon oils) or cyclic molecules (Figure 16.1) [9-12]. The cyclic PDMS include hexamethylcyclotrisiloxane (D3), octamethyl-cyclotetrasiloxane (OMCTS, D4), decamethylcyclopen-tasiloxane (D5), and dodecamethylcyclohexasiloxane (D6). A scheme for the classification of linear and cyclic... 

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