A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface‐grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact.
Simulations of polymerization rate, molecular weight development and evolution of the concentrations of species participating in the reaction mechanism over a range of operating conditions, and a parameter sensitivity analysis showing the effects of temperature, activation/deactivation equilibrium constant and initial concentrations of controller and initiator (if present) on these variables are presented for the nitroxide‐mediated radical polymerization of styrene. The simulations were performed with a computer program based on a detailed reaction mechanism. The simulated profiles of conversion, number average molecular weight ( ), and polydispersity agree well with experimental data. Previously unknown activation energies for reactions involved in the mechanism are estimated. The temperature dependence of the kinetic rate constants obtained in this study will be useful for future modeling and optimization studies.
Water‐soluble single‐ and multi‐walled carbon nanotubes (CNTs) were prepared by grafting polyacrylamide chains from the graphitic surface via ceric ion‐induced redox radical polymerization. The reducing functionalities were covalently attached to the tubes by peroxide‐assisted radical reaction. The results showed that polymer chains were grafted onto CNTs by the redox process. The redox radical polymerization initiated by carbon nanotube‐bearing functionalities not only provides a powerful strategy for modifying the carbon nanostructures but also gives us the knowledge of their sidewall chemistry.
A polyvinylpyrrolidone (PVP)‐based fluorescent film with stable optical properties is successfully prepared in one pot without any additive. The reaction mechanism of ring‐opening and self‐crosslinking of linear PVP is proposed and demonstrated. The morphologies and the nanostructures of the fluorescent film as well as the unmodified film are investigated. The dye is incorporated into the film networks via covalent linkages, thus leading to the highly stable optical properties. The facile and effective synthesis approach opens a new way for the design of other multi‐functional composite materials based on linear PVP.
Kinetic modeling is used to better understand and optimize initiators for continuous activator regeneration atom‐transfer radical polymerization (ICAR ATRP). The polymerization conditions are adjusted as a function of the ATRP catalyst reactivity for two monomers, methyl methacrylate and styrene. In order to prepare a well‐controlled ICAR ATRP process with a low catalyst amount (ppm level), a sufficiently low initial concentration of conventional radical initiator relative to the initial ATRP initiator is required. In some cases, stepwise addition of a conventional radical initiator is needed to reach high conversion. Under such conditions, the equilibrium of the activation/deactivation process for macromolecular species can be established already at low conversion.
Here, we show that a poly(ethylene oxide) polymer can be physically cross‐linked with silicate nanoparticles (Laponite) to yield highly extensible, bio‐nanocomposite fibers that, upon pulling, stretch to extreme lengths and crystallize polymer chains. We find that both, nanometer structures and mechanical properties of the fibers respond to mechanical deformation by exhibiting strain‐induced crystallization and high elongation. We explore the structural characteristics using X‐ray scattering and the mechanical properties of the dried fibers made from hydrogels in order to determine feasibility for eventual biomedical use and to map out directions for further materials development.
Novel wormlike nanostructures were self‐assembled in bulk films of a well defined diblock copolymer with azobenzene moieties, which was prepared by atom transfer radical polymerization (ATRP). For comparison, a homopolymer with almost the same repeat units of azobenzene as those in the copolymer was also prepared. They both had well defined structures and exhibited a smectic liquid crystalline phase. Upon annealing the copolymer films, poly(methyl methacrylate) formed a matrix with excellent optical properties, and the azobenzene segment in the minority phase self‐assembled into a wormlike mesogenic domain in the bulk films. Such block copolymer films exhibited stability and transparency by eliminating the scattering of visible light, indicating their potential application as photoresponsive functional materials. Although wormlike morphologies have been obtained in micelles from block copolymer solutions, to the best of our knowledge, such wormlike nanostructures have never been explored in bulk films.
Summary: Water‐soluble biomimetic chitosan derivative conjugating zwitterionic phosphorylcholine was efficiently prepared through Atherton‐Todd reaction under the mild conditions, and the possible formation mechanism of zwitterionic product was related to the nucleophilic attack of adjacent 3‐hydroxyl on the D ‐glucosamine residue to phosphorus with the help of base. UV absorption and melting behaviors of DNA/phosphorylcholine‐bound chitosan derivative showed that the phosphorylcholine‐bound chitosan derivative could be a new carrier for long‐circulating macromolecular drug delivery.
Well‐defined amphiphilic PCL‐b‐PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and “click” chemistry following either a commutative two‐step procedure or a straightforward one‐pot process using CuBr · 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a “one‐pot” process allows the preparation of PCL‐b‐PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.
A series of size‐controlled, cyclic poly(tetrahydrofuran)s ( of 4 400–8 600) that consist exclusively of the monomer, i.e., oxytetramethylene, unit ( I ) have been prepared in high yield through the metathesis polymer cyclization of a telechelic precursor having allyl groups, 1 , in the presence of a Grubbs catalyst, and the subsequent hydrogenation of the linking, i.e., 2‐butenoxy, unit in the presence of an Adams' catalyst (PtO2). A remarkable topology effect has subsequently been observed upon the isothermal crystallization of these two model polymers, showing distinctive spherulite growth rates and spherulite morphologies in comparison with the relevant linear poly(tetrahydrofuran) counterpart that has ethoxy end groups ( II ).
Initiators for continuous activator regeneration in atom transfer radical polymerization (ICAR ATRP) is a new technique for conducting ATRP. ICAR ATRP has many strong advantages over normal ATRP, such as forming the reductive transition metal species in situ using oxidatively stable transition metal species and a lower amount of metal catalyst in comparison with the normal ATRP system. In this work, the iron‐mediated ICAR ATRP of styrene and methyl methacrylate are reported for the first time using oxidatively stable FeCl3 · 6H2O as the catalyst in the absence of any thermal radical initiator. The kinetics of the polymerizations and effect of different polymerization conditions are studied. It is found that the polymerization of styrene can be conducted well even if the amount of iron(III ) is as low as 50 ppm.
It is demonstrated that an optically transparent and electrically conductive polyethylene oxide (PEO) film is fabricated by the introduction of individualized single‐walled carbon nanotubes (SWNTs). The incorporated SWNTs in the PEO film sustain their intrinsic electronic and optical properties and, in addition, the intrinsic properties of the polymer matrix are retained. The individualized SWNTs with smaller diameter provide high transmittance as well as good electrical conductivity in PEO films.
Summary: The synthesis of well‐defined uniform and spherical sub‐micron polymeric spheres, specifically poly[styrene‐co‐(glycidyl methacrylate)] (PSGMA) with a uniform size distribution and surface chemical functionality, is described. It is shown that the surface can be modified with a multi‐amine functional polymer, polyethyleneimine (PEI), most likely through covalent bonding in addition to electrostatic attraction. The PEI acts both as a stabilizing agent and a complexation agent for the deposition of noble metal Ag nanoparticles.
Reaction of PSGMA samples with excess PEI, and its TEM image. 相似文献
Tertiary amines were found to remarkably enhance the catalytic activity of ATRP catalysts CuBr/tris[(2‐pyridyl)methyl]amine and CuBr/tris[2‐(dimethylamino)ethylamine]. These two catalysts alone failed to polymerize MA, MMA, and styrene at reduced catalyst concentrations. With tertiary amines such as triethylamine both catalysts could mediate fast polymerizations of the three monomers in a controlled manner at as low as 1 mol‐% catalyst relative to initiator. A mechanism study showed that tertiary amines reduced copper(II) complexes to active copper(I) complexes.
The precipitation polymerization of styrene‐trihydroxymethyl propane triacrylate has been carried out using ethanol and an ethanol/water mixture as the solvent. Uniform microspheres with high monomer conversion are achieved within 4 h, a much shorter polymerization time than that reported for the precipitation polymerization of divinyl benzene‐styrene in acetonitrile. The results clearly demonstrate that use of water as a co‐solvent is indeed very effective to promote the polymerization to high conversion and to obtain uniform microspheres. With no water under the otherwise same experimental conditions, only about 57% of monomer conversion is obtained; while the monomer conversion is remarkably increased to 96% when 12 vol.‐% of water is used.
This review covers the literature concerning the modification of polysaccharides through controlled radical polymerizations (NMP, ATRP and RAFT). The different routes to well‐defined polysaccharide‐based macromolecules (block and graft copolymers) and graft‐functionalized polysaccharide surfaces as well as the applications of these polysaccharide‐based hybrids are extensively discussed.
The iron(III)‐catalyzed atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully employed using tributylphosphine (TBP) and trimethylphosphite (TMP) as ligands in the absence of a reducing agent. The effects of solvent and initiator on polymerization of MMA were investigated. Most of the polymerizations with these ligands were well controlled with a linear increase in the number average molecular weights ( ) versus conversion and relatively low molecular weight distribution ( = 1.2–1.4) throughout the reactions, and the measured weights matched with the predicted values. The ethyl 2‐bromoisobutyrate (EBriB) initiated ATRP of MMA with the FeBr3/TBP or FeBr3/TMP catalytic system was better controlled in toluene than in the other solvents used in this study at 80 °C.
Amphiphilic star shaped polymers with poly(ethylene oxide) (PEO) arms and cross‐linked hydrophobic core were synthesized in water via either conventional free radical polymerization (FRP) or atom transfer radical polymerization (ATRP) techniques using a simple “arm‐first” method. In FRP, PEO based macromonomers (MM) were used as arm precursors, which were then cross‐linked by divinylbenzene (DVB) using 2,2′‐azoisobutyronitrile (AIBN). Uniform star polymers ( < 1.2) were achieved through adjustment of the ratio of PEO MM, DVB, and AIBN. While in case of ATRP, both PEO MM, and PEO based macroinitiator (MI) were used as arm precursors with ethylene glycol diacrylate as cross‐linker. Even more uniform star polymers with less contamination by low MW polymers were obtained, as compared to the products synthesized by FRP.
Summary: A series of novel mesogen‐jacketed liquid crystal miktoarm star rod‐coil block copolymers were synthesized via atom transfer radical polymerization (ATRP). Their architectures {coil conformation of styrene segment and rigid rod conformation of {2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene} (MPCS) segment} were confirmed by GPC, 1H NMR, and MALDI‐TOF studies. The liquid crystalline behaviors of the synthesized copolymers are evidenced from POM observation. The liquid crystalline phase depends on the molecular weights of the rigid rod arm of miktoarm star copolymers.
