Synthesis and solution properties of well-defined comb-on-comb graft polymers
2008
Sun, Wei | Yu, Fengping | He, Junpo | Zhang, Chao | Yang, Yuliang
Well-defined comb-on-comb copolymers of styrene, isoprene, and α-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(α-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, Rg, 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 hard sphere to cylindrical rod, depending on the length ratio of the main chain to the branches.
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