Foamed polysiloxanes with

An important route to the production of foamed polysiloxane rubbers relies on the use of a low molecular weight silicone gum and on a series of tin catalysed cure and gas formation reactions. Normally, a dihydroxy terminated poly dimethylsiloxane containing a small amount of silica filler, together with a polyfunctional crosslinking agent (e.g. tetrapropylsilicate), is used as the starting material. 

Chem. Descrip. Polysiloxane-polyether copolymer surfactant Uses Foam stabilizer for rigid PU foams, continuously laminated PU boardstock, modified polyisocyanurate foams, spray foams synergistic with flame retardants Properties Cl. vise, liq. sp.gr. 1.072 0.01 g/cc vise. 730 150 mPa-s f.p. < 10 C ... 

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... 

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. 

Weighed amounts of bio-polyols, catalyst (Stannous 2-ethyl hexanoate), surfaetant (polyether-modified polysiloxane), and blowing reagent (distilled water) were mixed well in a paper cup. A prescribed amoimt of MDI was added to the mixture, which was then stirred with a high-speed stirrer (5,000 rpm) for 15 s. After stirring, the mixture was poured immediately into another paper cup, and the foam was allowed to rise and set at ambient conditions (22 °C). Finally, the foam samples were cured at room temperature for 24 h before any analysis can be conducted. The formulations of the prepared foams are shown in Table 2. 

The formation of cellular products also requires surfactants to facilitate the formation of small bubbles necessary for a fine-cell structure. The most effective surfactants are polyoxyalkylene-polysiloxane copolymers. The length and ethylene oxide/PO (EO/PO) ratio of the pendant polyether chains determine the emulsification and stabilizing properties. In view of the complexity of the interaction of surfactant molecules with the growing polymer chains in foam production, it is essential to design optimal surfactants for each application. Flexible polyurethane foams require surfactants that promote improved cell-wall drainage. This allows the cell walls to become more open during the foaming reaction. Also, the shift away from TDI to MDI in molded HR foams adds new demands on foam surfactants (97). 

The convenient properties of liquid and solid dimethylpolysiloxanes (thermal and chemical stability, hydrophobicity, anti-adhesive behavior, etc.) make them suitable for a variety of technical applications in medicine. Especially pure preparations (Silastic ) have been used to construct artificial limbs, gullets, cardiac valves, trachea, etc., and in face-lifting. Silicon rubber breast implants, which are filled with a polysiloxane gel, have been used cosmetically. Synthetic arteries impregnated with silicon do not break or cause coagulation, they are flexible, and they are well tolerated immunologically. Silicones prevent the formation of foam in equipment for artificial blood circulation (heart-lung machines). The surfaces of such equipment, and of the... 

Mono- and di-fatty-amides are used as antifoams [6,66,67]. Monoamides are active at levels as low as 1%. Diamides are, in most cases, used in combination with polysiloxanes, hydrocarbons, or soaps. Foam killing depends on chain length [68], as does soap, but not on water hardness. 

Disperse the titanium dioxide 2190 ( Ex Kronos) in Orotan 165 (Rohm Haas, anionic dispersant) and Disperse Ayd W22 (Daniel Products, surfactant), with water as carrier. Antifoam (Byk 035 from Byk Chemie) and flash rust inhibitor (Emadox NA from Labema) are added. When dispersed, add the pigment paste to the let down mix. Add butyl benzyl phthalate plasticiser and Dehydran 1293 (modified polysiloxane defoamer from Henkel, to reduce foam formation on application) and mix well. Adjust viscosity with water. Neocryl A633 is a 42%nvc acrylic/styrene dispersion from Zeneca. Silwet L-77 (Osi) is a nonionic silicone surfactant to improve wetting. 

Chem. Descrip. Polysiloxane-polyether block copolymer Uses Foam stabilizer and emulsifier for rigid PU and polyisocyanurate foams with max. demand on flow properties esp. for refrigeration and pipe insulation Properties Cl, vise, liq, sol. in common rigid foam polyols and resin preblends dens. 1,055 0,01 g/cc vise. 750 170 mPa-s solid, pt. < -8 C hyd. no. 100 10 cloud pt. 70 3 C (4% aq.) pH 6.5 1.5 (4% aq.)... 

Surfactants based on block copolymers of dimethylsiloxane with poly(ethylene oxide) are unique in regulating the cell size in polyurethane foams. One route to such polymers uses reaction I.E in Table 17.6 between a polysiloxane and an allyl ether of polyethylene oxide [11], Increasing the silicone content makes the surfactant more lipophilic (oil-loving), whereas increasing the poly(ethylene oxide) content makes it more hydrophilic (water-loving). 

Pashinin, V. L, Kozlov,V. T., Tarasova, Z. N., Safonova, G. V. Kauch., Rezina (Russian), Correlation of structural characteristics with the properties of irradiated polysiloxane rubber foams, Kauch.Rezina, (10), 18-21(1981)... 

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