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

Abstract

Ruthenium-catalyzed living radical polymerization was applied to the synthesis of a series of all methacrylic well-defined AxBAx-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 AxBAx 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.