Sealants thioether

Two of the more recendy developed polysulftde polymers are the mercaptan-terminated polyoxypropylene urethane polymer and the polythioether polymer. The urethane-backbone-based polymer is used in many sealant formulations for insulating glass appHcations. The thioether backbone contains sulfur, but no S—S bonds, which are the weakest part of the conventional polysulftde polymer. This polymer improves the thermal stabiHty and reduces the gas—Hquid permeabiHty. 

Most conventionalr polysulfide sealants are based on disulfides. Recently, a new family of sulfur-containing sealants (121,122) has been developed based on thioethers (Fig. 19) The thioether structure is thermally more stable than the polysulfide, thus the upper operating temperature... 

Though thioether sealants are somewhat more thermally stable than polysulfides, they are still not qualified as the advanced sealants for aerospace applications in severe environments. In the following section, we shall discuss some of the advanced sealants being considered for future applications. 

J. W. Huff andH. Singh, "New High Tempera re and Fuel Resistant Sealants Based on Permapol vS P-3 Poly-thioether Polymers," a technical publication by Products Research Chemical Corp., Glendale, California. 

The aliphatic thioethers (polysulfides) are unique among condensation polymers in being produced in an emulsion polymerization. The rank jr (Table 17.2, II.C) has an influence on the number of sulfur atoms in each polymer linkage. The tacky or liquid polymers are cast or applied as pastes in the case of sealants. The sulfur analog of poly(phenylene oxide) is poly(phenylene sulfide) (Table 17.2, II.C), which can be made by a condensation reaction between p-dichlorobenzene and sodium sulfide. The highly crystalline polymer is solvent resistant and has a low coefficient of friction. It can be injection molded at about 300°C and can also be used as a powder spray coating. 

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