Arborescent Polystyrene-<i>g</i><i>raft</i>-poly(2-vinylpyridine) Copolymers:  Synthesis and Enhanced Polyelectrolyte Effect in Solution

Abstract

A technique is described for the preparation of arborescent copolymers containing poly(2-vinylpyridine) (P2VP) segments. 2-Vinylpyridine is first polymerized with 1,1-diphenyl-2-methylpentyllithium in tetrahydrofuran in the presence of N, N, N ‘, N ‘ -tetramethylethylenediamine (TMEDA). The graft copolymers are obtained by titration of the P2VP anions with a solution of a chloromethylated polystyrene substrate. Copolymers incorporating either short ( M w ≈ 5000) or long ( M w ≈ 30 000) P2VP side chains were prepared by grafting onto linear, comb-branched (G0), G1, and G2 chloromethylated arborescent polystyrenes. Branching functionalities ranging from 14 to 3880 and molecular weights ranging from 8.2 × 10 4 to 6.7 × 10 7 were obtained for the copolymers, while maintaining a low apparent polydispersity ( M w / M n ≈ 1.06−1.15) after grafting. Characterization data for these materials from size exclusion chromatography and light scattering indicate that they have a highly compact structure. Dynamic light scattering results show that the arborescent poly(2-vinylpyridine) copolymers expand much more in solution than the linear homologous polymers when protonated with HCl. This is attributed to the higher charge density attained in the branched copolymers.