Bromination and Lithiation: Two Important Steps in the Functionalization of Polystyrene Resins

Reactions used for the bromination and lithiation of cross-linked polystyrene resins have been explored. In the presence of bromine and catalytic amounts of a thallium(III) salt, polystyrene resins are smoothly brominated and give homogeneous reactive resins with a highly reproducible degree of functionalization. These resins can be lithiated easily by reaction with an excess of n-butyllithium in benzene. Other swelling agents such as tetrahydrofuran gave incomplete removal of the bromine. The direct lithiation of polystyrene with n-butyllithium and tetramethylethylenediamine gave lithiated polymers containing approximately 2 mequiv of functional group per gram, while direct lithiation in the presence of triethylenediamine gave lower degrees of functionalization. The lithiated resins were used to prepare polymers containing carboxylic acid, thiol, sulfide, boronic acid, amide, silyl chloride, phosphine, alkl bromide, aldehyde, alcohol, or trityl functional groups for applications in polymer-assisted syntheses.