End group functionality of 95–99% : epoxide functionalization of polystyryl-lithium evaluated via solvent gradient interaction chromatography

Abstract

End group functionality is a key parameter of functional polymer chains. The end-capping efficiency of living polystyryl lithium with various epoxides, namely ethylene oxide (EO), ethoxy ethyl glycidyl ether (EEGE) and isopropylidene glyceryl glycidyl ether (IGG), is investigated with solvent gradient interaction chromatography (SGIC). Generally, end-capping efficiencies >95% are observed. Hydroxy functional polystyrene (PS–OH, PS–EEGE–OH, and PS–IGG–OH) with molar masses ranging from 13.8 to 15.0 kg mol−1 are obtained, with dispersities of 1.05–1.06. Deprotection of the acetal (PS–EEGE–OH) and ketal protective group (PS–IGG–OH) is investigated. Nearly quantitative deprotection (>99%) resulting in the corresponding multihydroxy functional PS (PS–(OH)2 and PS–(OH)3) are observed via SGIC. Esterification of PS–OH with succinic anhydride shows a conversion of 98% to the corresponding ester. A detailed picture of side reactions during the carbanionic polymer synthesis subsequent epoxide termination is obtained, demonstrating 95–99% terminal functionality. Depending on the polarity of the end group, an elution order of PS–OH < PS–(OH)2 < PS–(OH)3 < PS–COOH is obtained in SGIC. The study demonstrates both the analytical power of SGIC and the exceptionally high terminal functionalization efficiency of anionic polymerization methods.