Ling-Ying Shi

Covalent modification of graphene as a 2D nanofiller for enhanced mechanical performance of poly(glutamate) hybrid gels

Graphene-based materials usually require defined functionalization for biological applications in order to control their physical/colloidal properties and to introduce additional capabilities. Here, poly(glutamate), a competitive polypeptide, is covalently grafted onto the graphene oxide two-dimensional (2D) structure through the combination of amidation reaction and ring-opening polymerization as the nanofiller of a hybrid polypeptide-based organogel with enhanced mechanical performance. The morphologies of the hybrid gels reveal that the modified graphene nanostructures may act as nanoscale skeletons, interfacial adhesives in the hybrid gels with nanofibrous 3D network nanostructures.

Synthesis of pH-responsive amphiphilic branched macro-RAFT agent and the application in surfactant-free emulsion polymerization

Branched polymers have obviously different physical properties from their linear analogues such as low viscosity, high solubility, uncommon rheological properties and large amounts of functional groups. A series of branched poly(methyl acrylate)-block-poly(acrylic acid)s (PMA-b-HBPAAs) and branched poly(acrylic acid)-block-poly(methyl acrylate)s (PAA-b-HBPMAs) were successfully synthesized via RAFT polymerization using polyethylene glycol dimethacrylate (PEGDMA) as a branching agent, followed by a hydrolysis reaction. The structure of the branched copolymer was confirmed by Gel Permeation Chromatography (GPC), proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectrometry (FT-IR). Then the emulsifying performance and pH responsive behavior of these amphiphilic branched macromolecules were investigated. Furthermore, these amphiphilic branched macromolecules were used as surfactants and polymerization mediators for emulsion polymerization of styrene (St) at two pH (5.5 and 12.6), respectively. Due to the balanced hydrophilicity and hydrophobicity, PMA80-b-HBPAA120 proved to be an efficient surfactant both at pH = 12.6 and pH = 5.5. The influence of the pH, the length of the hydrophilic block of the PAA segments and hydrophobic PMA segments of the amphiphilic branched macromolecule have been studied.

A novel self-assembled hybrid organogel of polypeptide-based block copolymers with inclusion of polypeptide-functionalized graphene

Self-assembled hybrid organogels of polypeptides containing block copolymers with the inclusion of polypeptide-functionalized graphene were designed and elaborately prepared, and showed interesting microstructures as well as enhanced mechanical performances. Firstly, a series of peptide-based triblock copolymers (triBCPs), poly(γ-benzyl-L-glutamate)-b-poly-(dimethylsiloxane)-b-poly(γ-benzyl-L-glutamate) (PBLG-b-PDMS-b-PBLG, BDB), with different lengths of PBLG helices, were synthesized and characterized. As the length of the PBLG helices increased, the critical gelation concentration of the BDB triBCPs decreased while the gel–sol transition temperature increased. Moreover, the PBLG covalently modified graphene oxide (GO) sheets were successfully incorporated into the BDB organogels in toluene and hybrid organogels were prepared. In the presence of GO sheets, the minimum gelation concentration of the hybrid organogel was slightly lowered, and the hybrid organogels preserved thermoreversibility. In the hybrid gels, the triBCPs still self-assembled into nanoribbon structures and the functionalized GO sheets were well dispersed in the gel medium, which was obviously observed by transmission electron microscopy. In addition, the inclusion of the functionalized graphene greatly enhanced the mechanical performance of the hybrid gels, which was demonstrated by the significant increase of the moduli and the fracture stress of the hybrid gels compared with the corresponding native gels in the rheology experiments.