Polysulfides reactive type

Table 13.3.18 shows the results of polycondensation. The polysulfides having inherent viscosities above 0.5 dLg" were readily obtained from two bis(2-chloroaciyloyl)ben-zene with or without use of phase transfer catalysts. These activated dichlorides are highly reactive, almost comparable to ordinary dicarboxyUc acid chlorides. The use of catalysts, such as DC-18-C-6, was not essential to this type of polycondensation for producing high molecular weight of polysulfides XIII. 

The elastomeric type sealants are chemically curing systems based on a limited variety of polymers. The best known of these being polysulfide, silicone (see Silicones structures), Polyurethane and the modified silicones, which are urethane prepolymers with reactive silane end groups. All these are available as single- or two-part systems. 

It is sometimes difficult to understand the action of additives in deformed rubber vulcanizates [40]. This is because different kinds of radicals can be formed, for example, sulfur radicals (—RS ) as well as hydrocarbon radicals (—R ). The former do not react with oxygen the second type forms peroxide radicals (—ROO ). The kinetics of degradation for the different types of radicals is shown in Fig. 3.41. From this plot, the activation energy for radical decomposition can be calculated. It was found that the order of radical decay is peroxy > carboxy > polysulfide. It has also been observed that the reactivities for secondary processes (i.e., extraction of labile hydrogen atoms) are just in the reverse order. 

In addition to various types of polysulfides reported previously, a new polysulfide has been synthesized using bischloroacetyl aromatic compounds, which are known to be highly reactive dichlorides. The two-phase polycondensation of bis(4-chloroacetylphenyl) ether XXII with 4,4 -oxybisbenzenethiol XI leading to polysulfide XXm was conducted at 30°C in a 1,2-dichloroethane-aqueous potassium hydroxide system [Eq.(10)]. ... 

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