Elastomeric siloxane polymers

Recently, Kolel-Veetil and Keller have modified this system to produce elastomeric networked polymers. The ambient-condition hydrosilation reactions between monomeric vinyl- or ethynyl-terminated carboranylenesiloxane and three different monomeric branched siloxane cross-linkers in hexane yielding these systems were catalyzed by the Karstedt catalyst.134 The reactions involving the vinyl-carboranylenesiloxane were reported to produce a set of completely hydrosilated networked polymers (105) (Fig. 65). In the case of the ethynyl monomer, the reactions were carried out at two different ratios, yielding a partially (106) and a com-... 

In the interest of producing elastomeric network polymers, Kolel-Veetil et al. reported the modification of the preceding hydrosilation reaction system. They reported the Karstedt catalyst-catalyzed ambient-condition hydrosilation reactions of a monomeric vinyl 14 or ethynyl-containing 17 carboranylenesiloxane with three different monomeric branched siloxane crossUnkers in hexane (Figure 15.19) [36]. The reactions involving the vinylcarboranylenesiloxane were reported to... 

Siloxane polymers have much higher permeability to gases than most other elastomeric materials. For this reason, they have long been of interest for gas separation membranes, the goal being to vary the basic siloxane structure to improve selectivity without decreasing permeability. Polysdoxanes for pervaporation separations have also been of considerable interest. The techniques employed in this area include NMR and fluorescence correlation spectroscopy and inverse gas chromatography. ... 

Silicone elastomers are well known for their superior resistance to elevated (and reduced) temperatures, with little or no loss of properties. Again, the siloxane polymer structure is responsible for properties not seen in carbon-based polymers one reason is the inherent flexibility of the siloxane molecule, and another is its greater resistance to oxidative degradation. When these basic properties are enhanced with appropriate heat-resistant fillers and additives (often iron oxide), a high temperature elastomeric adhesive can be made that will withstand heating in air for up to a year at 400 F without significant property losses. Resistance to even higher temperatures can be achieved for shorter times, as shown in Table 2. 

St. Clair et. al. investigated a series of maleimide and nadimide terminated polyimides and developed LARC-13 [8,9]. Changing the terminal group from maleimide to nadimide, the value of the lap shear strength of a titanium lap shear joint increased from 7 to 19 MPa [9]. They also added an elastomeric component to the adhesive formulation. The introduction of 15 wt% of a rubbery component, ATBN (amine terminated butadiene nitrile polymer) and ADMS (aniline terminated polydimethyl siloxane) enhanced the adhesive properties as follows 19 MPa to 25 MPa (ATBN) titanium T-peel strength 0.2 kN/m to 1.4... 

Incorporation of flexible siloxane spacers into side chain or main chain liquid crystalline polymers have been shown to drastically reduce the transition temperatures 255,267,271,272,277) anc[ aiso increase the response time of the resultant systems to the applied thermal, optical or electrical fields 350-353>. In addition, siloxanes also provided elastomeric properties and improved the processibility (solution or melt) of the resulting liquid crystalline copolymers. 

A typical synthetic route to the incorporation of pendent carboranyl units into a polymer chain is shown in scheme 3. Poly(o-carboranyl-organo-siloxane)s have been successfully prepared through hydrolysis of dimethyldichlorosilane in the presence of carboranedichloromethylsilane. The polymer has some of the elastomeric characteristics of the parent poly(siloxane) however, the thermal-oxidative cleavage of the o-carboranyl pendent group is reported to occurat lower temperatures than that for the thermooxidative cleavage of Si—O and Si—C bonds.10 Thermal studies have... 

Hydrolysis of a reactive silane derivative under the proper conditions first produces a silanol, but except in the case of a few that are exceptionally stable, this product is not isolated, since the acid or alkaline reagents that are normally present cause most silanols to condense rapidly to form siloxanes. The product generally isolated when a dialkyl-or diaryl-substituted silane is hydrolyzed is, of course, a mixture of cyclic polysiloxanes, (R2SiO)n, from which high polymers (often elastomeric) are obtained by catalytic rearrangement and polymerization reactions. 

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