Direct synthesis of novel acidic and zwitterionic block copolymers via TEMPO-mediated living free-radical polymerization

A series of novel acidic and zwitterionic water-soluble diblock copolymers has been synthesized directly (i.e. without protecting group chemistry) via the TEMPO-mediated living free-radical polymerization of various hydrophilic styrenic monomers. Ln all syntheses TEMPO-capped poly(sodium 4-styrenesulfonate) was utilized as a well-defined macro-initiator. Chain extension of this macro-initiator with 2-vinylpyridine proved very inefficient. Using 4-vinylbenzyltrimethylammonium chloride as comonomer led to an insoluble zwitterionic complex, whereas water-soluble zwitterionic block copolymers were obtained wi th 4-(dimethylamino)methylstyrene. Micellar solutions were obtained with the less hydrophilic 4-vinylbenzyl alcohol comonomer. A series of strong acid-weak acid block copolymers with varying sodium 4-styrene-sulfonate contents (20-80 mol%) were prepared via chain extension of the macro-initiator using sodium 4-styrenecarboxylate. These acidic block copolymers undergo reversible pH-induced aggregation in aqueous solution and C-13 n.m.r. spectroscopy studies suggest that the carboxylic acid block forms the hydrophobic micellar core. Dynamic light scattering studies indicate intensity-average micelle diameters of 20-60 nm. (C) 1999 Elsevier Science Ltd. All rights reserved.