Arboreseent polystyrene-graft-poly(2-vinylpyridine) copolymers as unimolecular micelles.: Synthesis from acetylated substrates

Branched copolymers with a dendritic structure were synthesized by grafting poly(2-vinylpyridine) (P2VP) side chains onto linear and arborescent polystyrene substrates of generations G0-G2 randomly functionalized with acetyl groups. The P2VP side chains were generated in tetrahydrofuran using 1,1-diphenyl-3-methylpentyllithium as the initiator. The living polymer was then titrated with a solution of acetylated substrate to yield the copolymer. The grafting yield reached 92-96% in the 0-25 degreesC range with LiCl as a reactivity modifier for the P2VP anions. Arborescent copolymers with M-w approximate to 5000 or 30 000 P2VP side chains were synthesized. The copolymers with short side chains contain 82-92 mol % P2VP units. For the long side chain systems, the P2VP content reaches over 97 mol %. These materials are characterized by a very compact structure, a narrow molecular weight distribution (M-w/M-n = 1.06-1.08), and a roughly geometric increase in branching functionality and molecular weight for successive generations. The copolymers derived from the linear polystyrene substrate aggregate when dissolved in aqueous HCl solutions. In contrast, copolymers based on G0-G2 substrates give unimolecular micellar solutions under the same conditions.