Polyether siloxanes

Surface active agents are important components of foam formulations. They decrease the surface tension of the system and facilitate the dispersion of water in the hydrophobic resin. In addition they can aid nucleation, stabilise the foam and control cell structure. A wide range of such agents, both ionic and non-ionic, has been used at various times but the success of the one-shot process has been due in no small measure to the development of the water-soluble polyether siloxanes. These are either block or graft copolymers of a polydimethylsiloxane with a polyalkylene oxide (the latter usually an ethylene oxide-propylene oxide copolymer). Since these materials are susceptible to hydrolysis they should be used within a few days of mixing with water. 

Surfactants are often added to PU reactants to serve as emulsifiers these polyether siloxanes improve the miscibilities of the reactants (polyisocyanate, polyol. 

Tphe surface activity of block copolymers containing dimethylsiloxane units as one component has received considerable attention. Silicone-poly ether block copolymers (1,2,3) have found commercial application, especially as surfactants in polyurethane foam manufacture. Silicone-polycarbonate (4, 5), -polystyrene (6, 7), -polyamide (8), -polymethyl methacrylate (9), and -polyphenylene ether (10) block copolymers all have surface-modifying effects, especially as additives in other polymeric systems. The behavior of several dimethylsiloxane-bisphenol A carbonate block copolymers spread at the air—water interface was described in a previous report from this laboratory (11). Noll et al. (12) have described the characteristics of spread films of some polyether—siloxane block co-... 

The surface active agent is an essential ingredient in formulations. It facilitates the dispersion of water (see below) in the hydrophobic resin by decreasing the surface tension of the system. In addition, it also aids nucleation, stabilizes the foam, and regulates the cell size and uniformity. A wide range of surfactants, both ionic and nonionic, have heen used at various times. Commonly used among them are the water-soluhle polyether siloxanes. 

Chem. Descrip. Emulsion of a polyether siloxane copolymer with fumed silica... 

Chem. Descrip. Polyether siloxane copolymer, silica-free... 

Chem. Descrip. Polyether siloxane copolymer, contg. fumed silica Uses Defoamer for water-based systems, flexographic inks, gravure inks, architectural coatings, industrial coatings, pigment cones. 

Chem. Desaip. Polyether siloxane copolymer in xylene/phenoxyethanol (4 1)... 

Chem. Descrip. Polyether siloxane copolymer Uses Handle modifier, slip agent, flow aid for water-based and solv.-based systems, leather top coats based on PU, acrylics, and NC Regulatory EINECS, DSL, MITI, AlCS, ECL listed (act. ingred.) Properties Clear liq. dens. 1.045-1.065 g/ml vise. 330-570 mPa s pH 5-8 100% act. 

In a,o)-siloxanes, a uniform structure is synthesized that is denoted ABA. When a bifunctional polyether, e.g., a polyether diol, reacts with a,co-siloxanes, polyether siloxanes with A[BA] , structure are obtained. Evidently there is no difference in the amount of modifications per molecule for the latter two structures. Trisiloxane copolymers based on HMTS differ insignificantly in their chain length. 

FIG. 7 General structure for polyether siloxanes (polydimethylsiloxane-polyoxyal-kylene copolymers). 

FIG. 9 Reaction of A -methylglucamine and an epoxy functional polyether siloxane copolymer. 

FIG. 11 Surface tension of a polyether siloxane and a typical organic surfactant, sodium decyl benzene sulfonate. (From Ref. 32.)... 

The first publication about diesel antifoams in 1966 described the use of polyether siloxanes [45]. At least 60% of the polyether, which is attached by Si-C linkages, is composed of EO or PO [46]. It was not until 20 years later that commercial interest was raised. Polyethersiloxanes were claimed in which at least 80% of the attached polyether is EO [47]. These antifoams are water-soluble and therefore partially incompatible with the hydrocarbon chains of the diesel fuel, which leads to their surface activity. 

When the content of PO of the polyether is increased, the solubility of the corresponding polyether siloxanes in water is gradually shifted to insoluble compounds. They may serve to separate excessive quantities of gas such as butane from crude oil and to reduce foaming [55]. These foams, termed micro gas dispersions, contain gas bubbles that are less than 50 pm in size and also referred to as kugel foam. Since the gas bubbles move independently in the liquid, they are distinguished from other foams. 

Linear polyether siloxanes with ABA structure have demonstrated their superior ability to reduce the coefficient of friction of coatings and improve the mar and scratch resistance [59]. A chain of 20-60 dimethysiloxane units ensures the formation of a silicone oil like film on the surface even at a dosage level of 0.1%, whereas the polyether end groups guarantee a sufficient compatibility with the coating system. Slip properties of the polyether siloxane films for practical applications are even better than with pure silicone oil films, which tear under relatively low pressure due to their low intermolecular forces. The friction of coating surfaces can be reduced by a factor of 10 by the addition of only 0.1% of silicone polyethers. 

Stable macroemulsions with relatively large antifoam droplets can also be accomplished with polyether siloxanes. The optimal size of the droplets depends on the application and varies in the range from 1 to 40 nm. 

Polyether siloxane Effect of LiC104 dopant on microstructure [40]... 

Polyether-siloxane organic-inorganic hybrid nanocomposites Structure, thermal aud electrical properties [74]... 

Name(s) PTFE-modified PE polymer (1), polyether-modified polydime-thylsiloxane (2), HD polyethylene wax (3), polyolefin coated with PTFE (4), polyethylene wax modified with PTTE (5), PTFE (6), polyether siloxane copolymers (7)... 

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