Nanocomposites Derived from Polymers and Inorganic Nanoparticles

Polymers are considered to be good hosting matrices for composite materials because they can easily be tailored to yield a variety of bulk physical properties. Moreover, organic polymers generally have long-term stability and good processability. Inorganic nanoparticles possess outstanding optical, catalytic, electronic and magnetic properties, which are significantly different their bulk states. By combining the attractive functionalities of both components, nanocomposites derived from organic polymers and inorganic nanoparticles are expected to display synergistically improved properties. The potential applications of the resultant nanocomposites are various, e.g. automotive, aerospace, opto-electronics, etc. Here, we review recent progress in polymer-based inorganic nanoparticle composites.open565

Synthesis of Edge-Selectively Functionalized Graphene Nanoplatelets and Its Application

Energy Conversion & StorageI contrived a new method that was named edge-functionalized graphite (EFG). Unlike chemical oxidation method, this method can functionalize only an edge of graphite as it can retains superb properties of graphite. The new edge-functionalization was divided into two groups. One is to use organic wedges via Friedel-Crafts acylation reaction with poly(phosphoric acid) (PPA)/phosphorous pentoxide (P2O5) medium. There are wedges of organic materials such as organic molecule, linear macromolecular, dendritic macromolecular. The resultant showed an improved dispersibility in various common organic solvents because of organic wedges. And also, EFG could become films form via a simply heat-treatment. That was nitrogen doped graphene films to display outstanding electrocatalytic activity for oxygen reduction reaction (ORR). The other is to use a mechano-chemical cracking via ball milling. Graphite was broken by force energy of metal ball and broken graphite was functionalized with organic material and then exfoliated into graphene. The resultant is highly dispersible in various solvents to self-exfoliate into single- and few-layer (≤5 layers) graphene nanosheets (GNs). This method is effective, and eco-friendly, edge functionalization of graphite without the basal plane oxidation by ball milling. Therefore, the newly developed ball milling approach, involving neither hazardous chemicals nor tedious procedures, outperforms current processes for mass production of high-quality graphene nanosheets (GNs) at an unprecedented low cost. The resultants (EFGnPs) were also used as electrocatalysts for ORR in an alkaline electrolyte. It was found that the edge polar nature of the newly prepared EFGnPs without heteroatom doping into their basal plane played an important role in regulating the ORR efficiency with the electrocatalytic activity in the order of SGnP > CSGnP > CGnP > HGnP > pristine graphite. More importantly, the sulfur-containing SGnP and CSGnP were found to have a superior ORR performance to commercially available platinum-based electrocatalyst.ope

Hyperbranched macromolecules: From synthesis to applications

Hyperbranched macromolecules (HMs, also called hyperbranched polymers) are highly branched three-dimensional (3D) structures in which all bonds converge to a focal point or core, and which have a multiplicity of reactive chain-ends. This review summarizes major types of synthetic strategies exploited to produce HMs, including the step-growth polycondensation, the self-condensing vinyl polymerization and ring opening polymerization. Compared to linear analogues, the globular and dendritic architectures of HMs endow new characteristics, such as abundant functional groups, intramolecular cavities, low viscosity, and high solubility. After discussing the general concepts, synthesis, and properties, various applications of HMs are also covered. HMs continue being materials for topical interest, and thus this review offers both concise summary for those new to the topic and for those with more experience in the field of HMs

"Direct" grafting of linear macromolecular "wedges" to the edge of pristine graphite to prepare edge-functionalized graphene-based polymer composites

The edges of pristine graphite were covalently grafted with para-poly(ether-ketone) (pPEK) in a mildly acidic polyphosphoric acid (PPA)/phosphorus pentoxide (P(2)O(5)) medium. The resulting pPEK grafted graphite (pPEK-g-graphite) showed that the pristine graphite had been exfoliated into a few layers of graphene platelets (graphene-like sheets), which were uniformly dispersed into a pPEK matrix. As a result, the tensile properties of pPEK-g-graphite films were greatly improved compared to those of controlled pPEK films. The origins of these enhanced mechanical properties were deduced from scanning electron microscope (SEM) images of fracture surfaces. Upon tracing wide-angle X-ray scattering (WAXS) patterns of the film under strain, the graphene-like sheets were further exfoliated by an applied shear force, suggesting that a toughening mechanism for the pPEK-g-graphite film occurred. This approach envisions that the "direct'' edge grafting of pristine graphite without pre-treatments such as corrosive oxidation and/or destructive sonication is a simple and efficient method to prepare graphene-based polymer composites with enhanced mechanical properties.close161

Strain-induced delamination of edge-grafted graphite

Edge-selectively grafted graphite (EGG) with poly(ether-ketone) was prepared by the Friedel-Crafts acylation in a mild polyphosphoric acid (PPA)-phosphorous pentoxide (P2O5) mixture. The homogeneous reaction dope was coagulated in air moisture at different temperatures. The morphology of expanded EGG was changed from balls, balls/rods and rods with respect to coagulation temperatures of 80, 60, 40 and 25 degrees C, respectively.close1

Edge-functionalized graphene-like platelets as a co-curing agent and a nanoscale additive to epoxy resin

A newly developed method for the edge-selective functionalization of "pristine" graphite with 4-aminobenzoic acid was applied for the synthesis of 4-aminobenzoyl-functionalized graphite (AB-graphite) through a "direct" Friedel-Crafts acylation in a polyphosphoric acid (PPA)/phosphorus pentoxide medium (P(2)O(5)). The AB moiety at the edge of the AB-graphite played the role of a molecular wedge to exfoliate the AB-graphite into individual graphene and graphene-like platelets upon dispersion in polar solvents. These were used as a co-curing agent and a nanoscale additive to epoxy resin. The physical properties of the resulting epoxy/AB-graphite composites were improved because of the efficient load transfer between the additive and epoxy matrix through covalent links.close191

Wedging graphite into graphene and graphene-like platelets by dendritic macromolecules

We report in situ 'direct' grafting of dendritic macromolecular wedges to the edges of 'pristine' graphite. Because of the three-dimensional molecular architectures, the solubility of dendritic macromolecules is profoundly improved compared with that of their linear analogues. As a result, the resultant macromolecular wedge grafted graphite disperses well in common solvents. On the basis of results from wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM), HPEK is selectively grafted at the edges of graphite. For the efficient delamination of graphite into graphene and graphene-like platelets, the dendritic macromolecules with numerous polar periphery groups not only acts as macromolecular wedges but provides chemical affinity to solvents.close7

Reinforcement of polystyrene using edge-styrene graphitic nanoplatelets

Edge-styrene graphitic nanoplatelets (StGnPs) were prepared by the in-situ mechanochemical reaction between graphite and styrene without additional chemical reaction (e.g. functionalization). The resultant StGnPs exhibited excellent properties including good dispersibility in organic solvents, to use an efficient reinforcing additive for polystyrene (PS) that is one of the most widely used plastics. StGnP/PS nanocomposites were prepared easily via a facile solution process method. Compared to pure PS, the StGnP/PS nano composites exhibited significantly enhanced mechanical properties (e.g., tensile strength, yield strength, Young's modulus, and tensile toughness) along with improved thermal stability. The StGnP/PS nanocomposites showed efficient load transfer from the PS matrix to the StGnPs because of the good dispersibility and compatibility of the StGnPs in the PS matrix. And also, the mechanochemical reaction showed that GnPs having remarkable compatibility of various polymers can be produced freely. (C) 2020 The Author(s). Published by Elsevier B.V