Synthesis and solution properties of well-defined comb-on-comb graft polymers

Well-defined comb-on-comb copolymers of styrene, isoprene, and alpha-methyl-styrene are prepared through cascade grafting-onto methods. The polymer main chain is prepared by nitroxide-mediated radical polymerization while the branches are prepared by anionic polymerization. The grafting-onto approach employs the coupling chemistry of macromolecular anions, such as polystyryllithium, polyisoprenyllithium, or poly(alpha-methylstyryl)lithium, toward either benzyl chloride or epoxy ring on precursor backbones. Thus a series of ABA-, ABB-, and ABC-type comb-on-comb copolymers are prepared and characterized by gel permeation chromatography equipped with a multi-angle laser light scattering detector and a viscometer. Unusual U-shaped dependences of radius of gyration, R-g, on molecular weight are observed for comb-on-comb products, which are attributable to delayed elution of the densely grafted copolymers from GPC columns. The result also shows that the comb-on-comb copolymers exhibit morphologies from bard sphere to cylindrical rod, depending on the length ratio of the main chain to the branches. (C) 2008 Wiley Periodicals, Inc.