Polysiloxane fibers

Alkoxysilanes undergo hydrolysis, condensation (catalysts for alkoxysilane hydrolysis are usually catalysts for condensation), and a bond formation stage under base as well as under acid catalyzed mechanisms. In addition to this reaction of silanols with hydroxyls of the fiber surface, the formation of polysiloxane structures also can take place. 

The unique surface characteristics of polysiloxanes mean that they are extensively used as surfactants. Silicone surfactants have been thoroughly studied and described in numerous articles. For an extensive, in-depth discussion of this subject, a recent chapter by Hill,476 and his introductory chapter in the monograph he later edited,477 are excellent references. In the latter monograph, many aspects of silicone surfactants are described in 12 chapters. In the introduction, Hill discusses the chemistry of silicone surfactants, surface activity, aggregation behavior of silicone surfactants in various media, and their key applications in polyurethane foam manufacture, in textile and fiber industry, in personal care, and in paint and coating industries. All this information (with 200 cited references) provides a broad background for the discussion of more specific issues covered in other chapters. Thus, surfactants based on silicone polyether co-polymers are surveyed.478 Novel siloxane surfactant structures,479 surface activity and aggregation phenomena,480 silicone surfactants application in the formation of polyurethane foam,481 foam control and... 

Development has been conducted to fabricate SiC-based matrix/Si-C-based fiber composites by polymer infiltration. Nicalon fibers are used, and various polymers such as polysilazanes, polysiloxanes, and polycarbosilanes are used to yield matrices of SiCO, SiNC, and SiC. As with CVI of SiC/SiC composites, carbon acts as an interface layer but does not result in stability at high temperatures. 

Other polymers like polypropylene or polystyrene modified by maleic anhydride or maleamide, with the add groups converted to amide, ester or ester chloride and then reacted on Nylon fibers, have been claimed in a Japanese patent (101). Two patents report grafting of olefinic polymers on polycaprolactam (102,103). Grafting of polysiloxanes on polyamides can be induced by X-rays (104). 

FIGURE 3. A schematic sketch of the polysiloxane used for rapidly curing coatings of optical glass fibers... 

POSS was mechanically dispersed in a functionalized polysiloxane gum using a speedimix (needs some details) and the mix cured using tin catalyzed condensation chemistry. Silica and Carbon nano fiber composites were produced by mixing the fiber into functionalized polysiloxane gum and the mix cured using tin catalyzed condensation chemistry. 

Not all copolymers which are produced by step-growth processes are random in nature. Block copolymers are also of major interest. An example of the synthesis of elastic polyurethane fibers was given in Section 1.5.4. Block and graft copolymers of polysiloxane-poly(alkylenc ethers) with segments like5-9 are used as surfactants in the production of polyurethane foams with uniform cell sizes. 

A typical example of a thermotropic liquid crystalline polymers is the polyesters and the mesogen substituted polysiloxane. The aromatic amide, the super strength fiber known commercially as Kevlar belongs to the lyotropic liquid crystalline polymers. The other important lyotropic liquid crystalline polymers are poly(7-benzyl-L-glutamate), abbreviated as PBLG, cellulose derivatives, the tobacco mosaic virus, etc. 

Polycarbosilanes can exhibit thermal stabilities greater than the analogous polysiloxane , contrary to their relative bond energies (Si—C, 78 kcalmol Si—O, 106 kcal mol" ). Thus polydimethylsilane is polymerized by heating the hexamer to 300-500°C, forming a product with thermal stability greater than 500°C and that can be spun into fiber, which in turn can be thermally oxidized, forming j5-silicon carbide, SifCHj) -,. 

R.M. Rocha, C.A.A. Cairo, M.L.A. Graca, Formation of carbon fiber-reinforced ceramic matrix composites with polysiloxane/silicon derived matrix. Materials Science and Engineering A 437(2006) 268-273... 

Figure 8-19. Both hair fibers extension cycled 200 times to 20% extension at 10% RH, put into water, and knotted. Fiber on the right treated with 3% cystine poly-siloxane prior to knotting. Note the lack of scale lifting from the polysiloxane-treated fiber. Reprinted with permission of the Journal of Cosmetic Science [67].

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