Synthesis of Arborescent Polystyrene-g-[ poly( 2-vinylpyridine)- bpolystyrene] Core- Shell- Corona Copolymers

Arborescent copolymers with a core-shell-corona (CSC) architecture, incorporating a polystyrene (PS) core, an inner shell of poly(2-vinylpyridine), P2VP, and a corona of PS chains, were obtained by anionic polymerization and grafting. Living PS-b-P2VP-Li block copolymers serving as side chains were obtained by capping polystyryllithium with 1,1-diphenylethylene before adding 2-vinylpyridine. A linear or arborescent (generation G0 - G3) PS substrate, randomly functionalized with acetyl or chloromethyl coupling sites, was then added to the PS-b-P2VP-Li solution for the grafting reaction. The grafting yield and the coupling efficiency observed in the synthesis of the arborescent PS-g-(P2VP-b-PS) copolymers were much lower than for analogous coupling reactions previously used to synthesize arborescent PS homopolymers and PS-g-P2VP copolymers from the same types of coupling sites. It was determined from static and dynamic light scattering analysis that PS-b-P2VP formed aggregates in THF, the solvent used for the synthesis. This presumably hindered coupling of the macroanions with the substrate, and explains the low grafting yield and coupling efficiency observed in these reactions. Purification of the crude products was also problematic due to the amphipolar character of the CSC copolymers and the block copolymer contaminant. A new fractionation method by cloud-point centrifugation was developed to purify copolymers of generations G1 and above. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1075-1085