Preparation of antistatic high‐density polyethylene composites based on synergistic effect of graphene nanoplatelets and multi‐walled carbon nanotubes

Graphene nanoplatelets are promising candidates for enhancing the electrical conductivity of composites. However, because of their poor dispersion, graphene nanoplatelets must be added in large amounts to achieve the desired electrical properties, but such large amounts limit the industrial application of graphene nanoplatelets. Multi‐walled carbon nanotubes also possess high electrical conductivity accompanied by poor dispersion. Therefore, a synergistic effect was generated between graphene nanoplatelets and multi‐walled carbon nanotubes and used for the first time to prepare antistatic materials with high‐density polyethylene via 1‐step melt blending. The synergistic effect makes it possible to significantly improve the electrical properties by adding a small amount of untreated graphene nanoplatelets and multi‐walled carbon nanotubes and increases the possibility of using graphene nanoplatelets in industrial applications. When only 1 wt% graphene nanoplatelets and 0.5 wt% multi‐walled carbon nanotubes were added, the surface and volume resistivity values of the composites were much lower than those of the composites that were only added 3 wt% graphene nanoplatelets. Additionally, as a result of the synergistic effect of graphene nanoplatelets and multi‐walled carbon nanotubes, the composites met the requirements for antistatic materials.     

Ring‐Opening Polymerization of Lactide with Group 3 Metal Complexes Supported by Dianionic Alkoxy‐Amino‐Bisphenolate Ligands: Combining High Activity,Productivity, and Selectivity

A series of new alkoxy‐amino‐bis(phenols) (H₂L 1 – 6 ) has been synthesized by Mannich condensations of substituted phenols, formaldehyde, and amino ethers or diamines. The coordination properties of these dianionic ligands towards yttrium, lanthanum, and neodymium have been studied. The resulting Group 3 metal complexes have been used as initiators for the ring‐opening polymerization of rac‐lactide to provide poly(lactic acid)s (PLAs). The polymerizations are living, as evidenced by the narrow polydispersities of the isolated polymers, together with the linear natures of number average molecular weight versus conversion plots and monomer‐to‐catalyst ratios. Complex [Y(L 6 ){N(SiHMe₂)₂}(THF)] ( 17 ) polymerized rac‐lactide to heterotactic PLA (P_r = 0.90 at 20 °C) and meso‐lactide to syndiotactic PLA (P_r = 0.75 at 20 °C). The in situ formation of [Y(L 6 )(OiPr)(THF)] ( 18 ) from 17 and 2‐propanol resulted in narrower molecular weight distributions (PDI = 1.06). With complex 18 , highly heterotactic PLAs with narrow molecular weight distributions were obtained with high activities and productivities at room temperature. The natures of the ligand substituents were shown to have a significant influence on the degree of control of the polymerizations, and in particular on the tacticity of the polymer.     

Manganese‐based transition metal complexes as new catalysts for olefin polymerizations

Three manganese complexes, Mn(acac)₃ (acac = acetylacetonate), Cp₂Mn (Cp = cyclopentadienyl), and Mn(salen)Cl [salen = 1,2‐cyclohexanediamino‐N,N′‐bis(3,5‐dit‐butyl‐salicylidene)], were used for ethylene and propylene polymerizations. These complexes, in combination with an alkylaluminum cocatalyst such as methylaluminoxane (MAO) or diethyl aluminum chloride (AlEt₂Cl), could promote ethylene polymerizations that yielded extremely high molecular weight linear polymers, but were inactive for propylene polymerizations. The counterparts supported on MgCl₂ showed activities even for propylene polymerizations and had remarkably enhanced activities for ethylene polymerizations. In the presence of an electron donor such as ethylbenzoate, the MgCl₂‐supported manganese‐based catalysts yielded a highly isotactic polypropylene with a high molecular weight. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3733–3738, 2001     

(Thiocarbonyl‐α‐thio)carboxylic acid derivatives as transfer agents in reversible addition–fragmentation chain‐transfer polymerizations

Ethyl S‐(thiobenzoyl)thioacetate, ethyl S‐thiobenzoyl‐2‐thiopropionate, and S‐(thiobenzoyl)thioglycolic acid were used as chain‐transfer agents for the reversible addition–fragmentation chain‐transfer (RAFT) polymerizations of styrene, methyl methacrylate, and butyl acrylate. Of these polymerizations, only those of styrene and butyl acrylate with any of the transfer agents showed molecular weight control corresponding to controlled/living polymerizations. The best molecular weight control was observed for the polymerizations of styrene and butyl acrylate with ethyl (S)‐thiobenzoyl‐2‐thiopropionate. Semiempirical PM3 calculations were performed for the investigation of the relative heats of reaction of the chain‐transfer equilibria between the aforementioned chain‐transfer agents and dimer radicals of the three monomers. The molecular weight control of the polymerizations correlated with the stability trend of the leaving‐group radical of the chain‐transfer agent. This relatively simple computational model offered some value in determining which transfer agents would show the best molecular weight control in RAFT polymerizations. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 555–563, 2002; DOI 10.1002/pola.10143     

Atom transfer radical polymerization of styrene using the novel initiator ethyl 2‐N,N‐(diethylamino)dithiocarbamoyl‐butyrate

The atom transfer radical polymerizations (ATRPs) of styrene initiated by a novel initiator, ethyl 2‐N,N‐(diethylamino)dithiocarbamoyl‐butyrate (EDDCB), in both bulk and solution were successfully carried out in the presence of copper(I) bromide (CuBr) and N,N,N′,N″,N″‐pentamethyldiethylenetriamine at 115 °C. The polymerization rate was first‐order with respect to the monomer concentration, and the molecular weights of the obtained polymers increased linearly with the monomer conversions with very narrow molecular weight distributions (as low as 1.17) up to higher conversions in both bulk and solution. The polymerization rate was influenced by various solvents in different degrees in the order of cyclohexanone > dimethylformamide > toluene. The molecular weight distributions of the produced polymers in cyclohexanone were higher than those in dimethylformamide and toluene. The results of ¹H NMR analysis and chain extension confirmed that well‐defined polystyrene bearing a photo‐labile N,N‐(diethylamino)dithiocarbamoyl group was obtained via ATRP of styrene with EDDCB as an initiator. The polymerization mechanism for this novel initiation system is a common ATRP process. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 32–41, 2006     

Nickel‐ and palladium‐catalyzed olefin polymerization under high pressures

The polymerization of 1‐hexene under high pressures (100–750 MPa) was investigated with nickel–α‐diimine complex/methylaluminoxane and palladium–α‐diimine complex/methylaluminoxane as catalyst systems. The catalytic activity of both the nickel and palladium complexes monotonously increased as pressure rose and became two to four times higher than that observed at atmospheric pressure. Palladium catalysts gave poly(1‐hexene)s with higher molecular weights under high pressure, whereas nickel‐catalyzed high‐pressure polymerizations gave polymers with higher molecular weights only at rather low monomer concentrations. The living‐like character in the palladium‐catalyzed polymerizations was somewhat enhanced under higher pressures, whereas the nickel‐catalyzed polymerizations under high pressures were not living. More branches were found in the polymers produced by nickel catalysts at higher pressures. The chain‐transfer reaction seemed to be accelerated by the high pressure in the nickel‐catalyzed reactions, although this was not apparent in the palladium‐catalyzed reactions. Dimers formed and were accompanied by high molecular weight polymers when nickel catalysts were used under high pressures and at high monomer concentrations. The possibility that very congested five‐coordinated species act as key intermediates for the dimerization is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 293–302, 2003     

Photoinduced controlled/living free‐radical polymerization of 4‐methacryloyl‐1,2,2,6,6‐pentamethyl‐piperidenyl

The photoinduced solution polymerization of 4‐methacryloyl‐1,2,2,6,6‐pentamethyl‐piperidinyl (MPMP), used as a reactive hindered amine piperidinol derivative, was performed. The obtained MPMP homopolymer had a very narrow molecular weight distribution (1.06–1.39) according to gel permeation chromatography. The number‐average and weight‐average molecular weights increased linearly with the monomer conversion, this being characteristic of controlled/living free‐radical polymerizations. Electron spin resonance signals were detected in the MPMP homopolymer and in a polymer mixture solution, and they were assigned to nitroxide radicals, which were bound to the polymer chains and persisted at a level of 10^?9 mol/L during the polymerization. Instead of the addition of mediated nitroxide radicals such as 2,2,6,6‐tetramethyl‐piperidinyl‐1‐oxy (TEMPO), those radicals (>N? O ·) were formed in situ during the photopolymerization of MPMP, and so the reaction mechanism was understood as being similar to that of TEMPO‐mediated controlled/living free‐radical polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2659–2665, 2004     

Edge‐Selectively Functionalized Graphene Nanoplatelets

Graphene, as a single layer of graphite, is currently the focal point of research into condensed matter owing to its promising properties, such as exceptional mechanical strength, high thermal conductivity, large specific surface area, and ultrahigh electron‐transport properties. Therefore, various physical and chemical synthetic procedures to prepare graphene and/or graphene nanoplatelets have been rapidly developed. Specifically, the synthesis of edge‐selectively functionalized graphene (EFG) has been recently reported by using simple and scalable approaches, such as “direct” Friedel‐Crafts acylation reactions in a mild acidic medium and a mechanochemical ball‐milling process. In these approaches, chemical functionalization predominantly take place at the edges of the graphitic layers via the covalent attachment of targeted organic “molecular wedges”. In addition, the distortion of the crystalline structures in the basal plane, which is beneficial for preserving the unique properties of the graphitic framework, can be minimized. In addition, the efficient exfoliation of graphene can be achieved, owing to the strong repulsive forces from the covalently linked wedges and strong shear forces during the reaction. Furthermore, EFG shows promising potential in many useful applications, such as highly conductive large‐area films, metal‐free electrocatalysts for the oxygen‐reduction reaction (ORR), and as additives in composite materials with enhanced properties. Herein, we summarize the recent progress and general aspects of EFG, including synthesis, reaction mechanism, properties, and applications.     

Influence of graphene nanoscrolls on the crystallization behavior and nano‐mechanical properties of polylactic acid

Graphene nanoscrolls (GNS), one‐dimensional carbon‐based nanomaterials, have been predicted to possess extraordinary characteristics due to their unique open topology with scrolled graphene monolayers. In this study, the conversion of planar 2‐D graphene nanoplatelets (GNPs) to tubular and scrolled 1‐D GNSs is described. The effects of GNS as a nucleating agent to modulate the morphology, crystallization, and nano‐mechanical properties of polylactic acid (PLA) were studied. The nucleating effect of GNS and its unique topological characteristics proves to influence the crystallization of PLA. Fourier transform infrared (FTIR) spectroscopy indicated nonpreferential interactions of PLA chains around GNS due to the bulky and helical PLA macromolecular chains. Superior interfacial interactions and strain in GNS provide better load transfer between GNS and PLA matrices, resulting in higher modulus and hardness. This study is the first detailed analysis to elucidate the role of unique GNS to favorably modulate the properties of a polymer.     

Isoselective Ring‐Opening Polymerization of rac‐Lactide Catalyzed by Sodium/potassium Tetradentate Aminobisphenolate Ion‐paired Complexes

Two sodium/potassium tetradentate aminobisphenolate ion‐paired complexes were synthesized and structurally characterized. These ion‐paired complexes are efficient catalysts for the ring‐opening polymerization of rac‐lactide (rac‐LA) in the presence of 5 equivalents BnOH as an initiator and the side reaction of epimerization can be suppressed well at low temperatures. The polymerizations are controllable, affording polylactides with desirable molecular weights and narrow molecular weight distributions; the highest molecular weight can reach 50.1 kg mol^?1 in this system, and a best isoselectivity of P_m=0.82 was achieved. Such polymerizations have rarely been reported for isoselective sodium/potassium complexes without crown ether as an auxiliary ligand. The solid structures suggest that BnOH can be activated by an interaction with the anion of sodium/potassium complex via a hydrogen bond and that the monomer is activated by coordination to sodium/potassium ion.     

2‐(2‐Aminoethylamino)‐5‐nitropyridine as a basic matrix for negative‐mode matrix‐assisted laser desorption/ionization analysis of phospholipids

Fast and easy analysis of phospholipids (PLs) by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) has been well demonstrated. However, when using common organic matrices, such as 2,5‐dihydroxybenzoic acid (DHB), the detection of most PL classes in positive‐ion mode is difficult when PLs containing zwitterionic groups, such as phosphatidylcholines (PCs) and sphingomyelins (SMs) are present. To reduce this limitation, 2‐(2‐aminoethyloamino)‐5‐nitropyridine (AAN), a basic compound, was evaluated as an alternative matrix. Negative‐ion spectra showed enhanced detection of phosphatidyl ethanolamines (PEs), phosphatidyl serines (PSs), phosphatidyl glycerols (PGs), and phosphatidyl inositols (PIs) in simple mixtures and in a crude methanolic soybean extract. The relative ionization efficiency (RIE) was highest for PIs and lowest for PGs, PSs, and PEs. Compared to DHB and para‐nitroaniline, AAN resulted in greater sensitivity for the detection of PL classes in the negative mode. Indeed, the S/N ratio was nearly an order of magnitude higher than that reported for similar PI concentrations but with DHB. MALDI spots produced with AAN were homogeneous thus allowing automation and improved reproducibility. Positive‐mode traces could also be acquired with AAN as the matrix, but with lower sensitivity than in the negative mode. Copyright © 2008 John Wiley & Sons, Ltd.     

Isomerization polymerization and copolymerization of glycidyl alkanoates catalyzed by methylaluminum bis(2,6‐di‐t‐butyl‐4‐methylphenoxide)

The isomerization polymerizations of glycidyl propionate (1b), octanoate (1c), and stearate (1d) with methylaluminum bis(2,6‐di‐tert‐butyl‐4‐methylphenoxide) (3) were investigated. The polymerizations selectively gave poly(2‐alkyl‐1,3‐dioxolane‐4,2‐diyloxymethylene)s (2), although the polymer yield as well as the polymer molecular weight significantly decreased as the acyl chain of 1 was lengthened. These polymers readily hydrolyzed to glycerin and the corresponding fatty acids under mild conditions. The copolymerizations of glycidyl acetate (1a) with these monomers were also examined. In any combination, the composition of the obtained copolymer was essentially identical with the feed ratio, while both copolymer yield and molecular weight decreased as the feed of 1a was decreased. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 435–444, 1999 (See graphics.)     

Developing Graphene‐Based Nanohybrids for Electrochemical Sensing

Graphene‐based nanohybrid is considered to be the most promising nanomaterial for electrochemical sensing applications due to the defects created on the graphene oxide layers. These defects provide graphene oxide unique properties, such as excellent conductivity, large specific surface area, and electrocatalytic activity. These unique properties encourage scientists to develop novel graphene‐based nanohybrids and improve the sensing efficiency. This review, therefore, addresses this topic by comprehensively discussing the strategies to fabricate novel graphene based nanohybrids with high sensitivity. The combinations of graphene with various nanomaterials, such as metal nanoclusters, metal compound nanoparticles, carbon materials, polymers and peptides, in the direction of electrochemical sensing, were systematically analyzed. Meanwhile, the challenges in the functional design and application of graphene‐based nanohybrids were described and the reasonable solutions were proposed.     

Reversible addition–fragmentation chain transfer polymerization of 2‐naphthyl acrylate with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate as a chain‐transfer agent

The reversible addition–fragmentation chain transfer (RAFT) polymerizations of 2‐naphthyl acrylate (2NA) initiated by 2,2′‐azobisisobutyronitrile were investigated with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as a RAFT agent at various temperatures in a benzene solution. The results of the polymerizations showed that 2NA could be polymerized in a controlled way by RAFT polymerization with CPDN as a RAFT agent; the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with the monomer conversion. The polydispersities of the polymer were relatively low up to high conversions in all cases. The chain‐extension reactions of poly(2‐naphthyl acrylate) (P2NA) with methyl methacrylate and styrene successfully yielded poly(2‐naphthyl acrylate)‐b‐poly(methyl methacrylate) and poly(2‐naphthyl acrylate)‐b‐polystyrene block polymers, respectively, with narrow polydispersities. The P2NA obtained by RAFT polymerization had a strong ultraviolet absorption at 270 nm, and the molecular weights had no apparent effect on the ultraviolet absorption intensities; however, the fluorescence intensity of P2NA increased as the molecular weight increased and was higher than that of 2NA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2632–2642, 2005     

Large‐Scale Synthesis of Highly Luminescent Perovskite‐Related CsPb2Br5 Nanoplatelets and Their Fast Anion Exchange

All‐inorganic cesium lead‐halide perovskite nanocrystals have emerged as attractive optoelectronic nanomaterials owing to their stabilities and highly efficient photoluminescence. Herein we report a new type of highly luminescent perovskite‐related CsPb₂Br₅ nanoplatelets synthesized by a facile precipitation reaction. The layered crystal structure of CsPb₂Br₅ promoted an anisotropic two‐dimensional (2D) crystal growth during the precipitation process, thus enabling the large‐scale synthesis of CsPb₂Br₅ nanoplatelets. Fast anion exchange has also been demonstrated in as‐synthesized CsPb₂Br₅ nanoplatelets to extend their photoluminescence spectra to the entire visible spectral region. The large‐scale synthesis and optical tunability of CsPb₂Br₅ nanoplatelets will be advantageous in future applications of optoelectronic devices.     

Bottom‐Up Fabrication of Single‐Layered Nitrogen‐Doped Graphene Quantum Dots through Intermolecular Carbonization Arrayed in a 2D Plane

A single‐layered intermolecular carbonization method was applied to synthesize single‐layered nitrogen‐doped graphene quantum dots (N‐GQDs) by using 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) as the only precursor. In this method, the gas produced in the pyrolysis of TATB assists with speeding up of the reactions and expanding the layered distance, so that it facilitates the formation of single‐layered N‐GQDs (about 80 %). The symmetric intermolecular carbonizations of TATB arrayed in a plane and six nitrogen‐containing groups ensure small, uniform sizes (2–5 nm) of the resulting products, and provide high nitrogen‐doping concentrations (N/C atomic ratio ca. 10.6 %). In addition to release of the produced gas, TATB is almost completely converted into aggregated N‐GQDs; thus, relatively higher production rates are possible with this approach. Investigations show that the as‐produced N‐GQDs have superior fluorescent characteristics; high water solubility, biocompatibility, and low toxicity; and are ready for potential applications, such as biomedical imaging and optoelectronic devices.     

Controlled synthesis of functionalized polymers by transition‐metal‐mediated living radical polymerization

This paper discusses recent progress in transition‐metal‐catalyzed living radical polymerizations, partly focusing on the search of metal complex catalysts that play a critical role in controlling polymer molecular weights, then‐distributions, and architectures. Following a brief overview of the design of initiating systems (initiators and metal catalysts), half‐metallocene‐type complex catalysts are presented that induce living radical polymerizations of methacrylates, acrylates, and styrene to give markedly narrow molecular weight distributions and controlled molecular weights. Some of these halfmetallocenes also work in water where suspension living radical polymerization is feasible.     

Mechanically Initiated Bulk‐Scale Free‐Radical Polymerization

Mechanical initiation of polymerization offers the chance to generate polymers in new environments using an energy source with unique capabilities. Recently, a renewed interest in mechanically controlled polymerization has yielded many techniques for controlled radical polymerization by ultrasound. However, other types of polymerizations induced by mechanical activation are rare, especially for generating high‐molecular‐weight polymers. Herein is an example of using piezoelectric ZnO nanoparticles to generate free‐radical species that initiate chain‐growth polymerization and polymer crosslinking. The fast generation of high amounts of reactive radicals enable the formation of polymer/gel by ultrasound activation. This chemistry can be used to harness mechanical energy for constructive purposes in polymeric materials and for controlled polymerizations for bulk‐scale reactions.     

Fluorene‐rich high performance polyesters: Synthesis and characterization of 9,9‐fluorenylidene and 2,7‐fluorenylene‐based polyesters with excellent optical property

Polyesters PEs containing high content of fluorene units in their backbones were synthesized from 9,9‐diarene‐substituted fluorene diols ( 1 ) and fluorene‐based diacid chlorides ( 2 ) by high temperature polycondensation at 185 °C in diphenyl ether. The molecular weights of the polyesters PE1‐PE5 were in a range of M_w 25,000–165,000. The polyesters displayed their high thermostability: the glass transition temperatures (T_g) by differential scanning calorimetry analysis ranged from 109 to 217 °C, while the 10% weight loss temperatures (T_d10) measured by thermogravimetric analysis were over 400 °C in nitrogen and 395 °C in air. The polyesters had good solubility in most common organic solvents such as chloroform and toluene and gave tough, transparent and flexible cast films. The transmittance of the films was over 80% in the wavelength range from 450 to 700 nm in any PEs . The PEs exhibited high refractive index values around 1.65, while they had very low degree of birefringence. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2549–2556, 2008     

Continuous Reversible Addition‐Fragmentation Chain Transfer Polymerization in Miniemulsion Utilizing a Multi‐Tube Reaction System

Summary: A unique, multi‐tube, continuous reactor has been successfully designed and implemented for the study of reversible addition‐fragmentation chain transfer (RAFT) in miniemulsions. Data collection is greatly enhanced by the ability to simultaneously collect samples at five different residence times. The results of a styrene homopolymerization show that kinetically, the reactor exhibits similar behavior to a batch reaction. Number‐average molecular weights increased linearly with conversion, typical of living polymerizations.

The number‐average molecular weight of the polymers produced in the tubular reactor increased linearly with conversion, indicative of a controlled polymerization.