A_xBA_x-Type Block-Graft Polymers with Middle Soft Segments and Outer Hard Graft Chains by Ruthenium-Catalyzed Living Radical Polymerization: Synthesis and Characterization

摘要

Ruthenium-catalyzed living radical polymerization was applied to the synthesis of a series of all methacrylic well-defined A_xBA_x-type block-graft copolymers consisting of soft middle segments [dodecyl methacrylate (DMA)] and hard outer graft chains [methyl methacrylate (MMA)] with controlled lengths of the backbone and graft chains and controlled graft numbers.This synthetic method was based on the CHCl2(COPh)/ Ru(Ind)Cl(PPh3)2-initiated sequential living radical block copolymerization of DMA and 2-(trimethylsilyoxy)-ethyl methacrylate (TMSHEMA) followed by the direct transformation of the silyloxy groups into the ester with C-Br bond by 2-bromoisobutyroyl bromide and the ruthenium-catalyzed "grafting-from" polymerization of MMA.A series of the block-graft copolymers were then characterized by NMR,size-exclusion chromatography (SEC),multiangle laser light scattering (MALLS),differential scanning calorimetry (DSC),dynamic viscoelasticity,transmission electron microscopy (TEM),and atomic force microscopy (AFM).The NMR and SEC-MALLS indicate the well-defined synthesis of the A_xB A_x block-graft copolymers with graft chains as branched structure.The DSC and viscoelasticity show the presence of two transitions suggesting a microphase separation,which was observed by TEM and proved different from that of the ABA triblock copolymer with the same composition.A visualization of single molecules by AFM was achieved for the first time to show the dumbbell-like structure.