Electrophilic chloromethylation polystyrene

Table 9.6 Reactions of calcium cuprate reagents from chloromethylated polystyrene and Rieke calcium with various electrophiles.

Anionic grafting methods (vide infra) can be applied to the synthesis of comb-shaped polymers. As an example, a polystyrene backbone is partially chloromethylated (under mild conditions) and used as an electrophilic deactivator for a living polystyrene 89). The grafting onto process yields well defined species that have been characterized accurately. The branches are distributed randomly along the backbone 90). 

Aromatic electrophilic substitution is used commercially to produce styrene polymers with ion-exchange properties by the incorporation of sulfonic acid or quaternary ammonium groups [Brydson, 1999 Lucas et al., 1980 Miller et al., 1963]. Crosslinked styrene-divinyl-benzene copolymers are used as the starting polymer to obtain insoluble final products, usually in the form of beads and also membranes. The use of polystyrene itself would yield soluble ion-exchange products. An anion-exchange product is obtained by chloromethylation followed by reaction with a tertiary amine (Eq. 9-38) while sulfonation yields a cation-exchange product (Eq. 9-39) ... 

Crosslinked polystyrene (copolymer with divinyl benzene) is now a favorite support material. Perhaps the main reason for choosing crosslinked polystyrene is that it can be functionalized in many ways. It can be nitrated, chloromethylated, sulfonated, lithiated, carboxylated, and acylated. The greatest use has been made of the chloromethylated and lithiated derivatives. This is because these two derivatives can react with nucleophilic and electrophilic reagents, respectively, resulting in a wide range of functionalized polymers. See Section 8.4.3 for an illustration. 

Polystyrene, chloromethylated PS, and lithiated PS rings are used in the modification of PS resins for the preparation of new functional polymers because they provide a method of attaching a wide variety of both electrophilic and nucleophilic species. However, the use of commercial PS beads in chemical modifications requires the removal of surface impurities such as suspending or stabilizing agents which remain from the polymerization process, since surface contaminants can prevent the penetration of reagents into the swollen beads or lead to the need for more drastic reaction conditions. 

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