Polyethene, cross-linking

Cross-linking in polyethene may be induced in the presence of a sen-sitiser such as benzophenone. The mechanism is outlined in Scheme 9.4, where the symbol Pn-H represents any C-H bond in polyethene. 

Exercise 29-6 Radical-induced chlorination of polyethene in the presence of sulfur dioxide produces a polymer with many chlorine and a few sulfonyl chlo-- ide (—S02CI) groups, substituted more or less randomly along the chains. Write suitable mechanisms for these substitution reactions. What kind of physical properties would you expect the chlorosulfonated polymer to have if substitution is carried to the point of having one substituent group to every 25 to 100 CH2 groups How may this polymer be cross-linked (A useful product of this general type is marketed under the name of Hypalon.)... 

Exercise 29-7 When polyethene (and other polymers) are irradiated with x rays, cross-links are formed between the chains. What changes in physical properties would you expect to accompany such cross-linking Would the polyethene become more flexible Explain. 

Suppose polyethene were cross-linked by irradiation at a temperature above Tm. What would happen if it were then cooled ... 

The mechanical properties of a polymer sample are determined by many factors. Resins vary from extremely flexible but shong rubbers to brittle weak materials such as the natural resins (Figure 2.11). Contrasts can be made in the ability to be stretched without permanent distortion (elasticity of cross-linked rubber), in the distortion caused by stretching (polyethene distorts if stfetched... 

Polyethene has been reacted with chlorosulfonic acid to form products containing SO3, OSO3, Cl, OH, CO and CO2 groups and double bonds which form cross-linking bridges and promote the entrance of further groups. The sulfur content of the products is dependent on the reaction temperature, the gel formation and the quantity of chlorosulfonic acid. The products were useful as cation-exchange polymers. ... 

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