Showing papers on "Copolymer published in 2001"
TL;DR: In this paper, a block copolymer of (ar-vinylbenzyl)trimethylammonium chloride with N,N-dimethylvinyl benzylbenzylamine has been synthesized, using the same methodology.
Abstract: Homopolymers of sodium 4-styrenesulfonate have been synthesized directly in aqueous media by reversible addition−fragmentation chain transfer polymerization (RAFT). The resulting homopolymers have narrow molecular weight distributions, with polydispersity indices in the range 1.12−1.25, as determined by aqueous size exclusion chromatography. Using a dithioester-capped sodium 4-styrenesulfonate homopolymer as a macro chain transfer agent, a block copolymer with sodium 4-vinylbenzoate has been prepared in aqueous media. Additionally, a block copolymer of (ar-vinylbenzyl)trimethylammonium chloride with N,N-dimethylvinylbenzylamine has been synthesized, using the same methodology. We believe these represent the first examples of AB diblock copolymers prepared directly in aqueous media via the RAFT process. Both block copolymers are stimuli-responsive and undergo reversible pH-induced micellization in aqueous solution. Micelles with hydrodynamic diameters in the range 18−38 nm were observed by dynamic light sc...
680 citations
TL;DR: In this article, the potential of block copolymer type macromolecular building blocks for the preparation of self-assembled materials is discussed, and several strategies are presented that could allow the preconditioning of stimuli-sensitive materials.
Abstract: This review discusses the potential of block copolymer type macromolecular building blocks for the preparation of self-assembled materials. Three different classes of block copolymer type architectures will be distinguished: i) coil-coil diblock copolymers, ii) rod-coil diblock copolymers, and iii) rod-coil diblock oligomers. The basic principles that underlie the self-assembly of each of these different building blocks will be discussed. These theoretical considerations are complemented with examples from recent literature that illustrate the potential of the different type of block copolymers to prepare (functional) supramolecular materials. Finally, several strategies will be presented that could allow the preparation of stimuli-sensitive self-assembled materials, i.e., materials whose properties can be reversibly manipulated under the action of appropriate external stimuli.
629 citations
Patent•
03 Apr 2001TL;DR: In this paper, the authors proposed a method for the synthesis of a multilayer polymeric coating with free isocyanate groups and free radical polymerization, which is different from A1 and A2.
Abstract: Coating compounds curable by means of high-energy radiation, comprising as binder A) at least one (meth)acrylic copolymer containing olefinic double bonds capable of free-radical polymerization and hydroxyl groups with a C═C equivalent weight from 100 to 10,000 and an OH-value from 20 to 250 mg KOH/g, which is prepared from monomers comprising: A1) at least one olefinically unsaturated, epoxy-functional monomer capable of free-radical polymerization, A2) at least one olefinically unsaturated, carboxy-functional monomer capable of free-radical polymerization and A3) at least one further olefinically unsaturated monomer capable of free-radical polymerization which is different from A1) and A2), and B) at least one component with free isocyanate groups and process for multilayer coating using the coating compounds
620 citations
TL;DR: The cytotoxic activity of the micelles against HepG2 cells was greater than free doxorubicin, suggesting that the miceLLes containing conjugated doxorbicin were more effectively taken up cellularly, by an endocytosis mechanism rather than by passive diffusion.
521 citations
TL;DR: In this article, a zirconium complex with two phenoxy−imine chelate ligands, bis[3-tert-butylsalicylidene)anilinato]zirconia(IV)dichloride (1), was found to display a very high ethylene polymerization activity with a viscosity average molecular weight (Mv) value of 0.9 × 104 at 25 °C at atmospheric pressure using methylalumoxane (MAO) as a cocatalyst.
Abstract: A zirconium complex having two phenoxy−imine chelate ligands, bis[N-(3-tert-butylsalicylidene)anilinato]zirconium(IV)dichloride (1), was found to display a very high ethylene polymerization activity of 550 kg of polymer/mmol of cat·h with a viscosity average molecular weight (Mv) value of 0.9 × 104 at 25 °C at atmospheric pressure using methylalumoxane (MAO) as a cocatalyst. This activity is 1 order of magnitude larger than that exhibited by Cp2ZrCl2 under the same polymerization conditions. The use of Ph3CB(C6F5)4/i-Bu3Al in place of MAO as a cocatalyst resulted in extremely high molecular weight polyethylene, Mv 505 × 104, with an activity of 11 kg of polymer/mmol of cat·h at 50 °C. This Mv value is one of the highest values displayed by homogeneous olefin polymerization catalysts. Complex 1, using Ph3CB(C6F5)4/i-Bu3Al as a cocatalyst, provided a high molecular weight ethylene−propylene copolymer, Mv 109 × 104, with 8 kg of polymer/mmol of cat·h activity at a propylene content of 20.7 mol %. X-ray analy...
441 citations
TL;DR: In this paper, the authors investigated the effect of different stabilizers on the catalytic activity and stability of transition metal nanoparticles in the Suzuki reaction in an aqueous medium, and found that the stability of the Pd nanoparticles is measured by the tendency of the nanoparticles to give Pd black powder after a catalytic reaction.
Abstract: Transition metal nanoparticles used in catalysis in solution are stabilized by capping the surfaces that are supposed to be used for catalysis. Determining how these two properties, that is, the catalytic activity and stability of nanoparticles, change as different capping materials are used is the aim of this work. Pd nanoparticles prepared by the reduction of metal salts in the presence of three different stabilizershydroxyl-terminated poly(amido-amine) (PAMAM) dendrimers (Gn-OH, where Gn represents the nth generation), block copolymer polystyrene-b-poly(sodium acrylate) and poly(N-vinyl-2-pyrrolidone) (PVP)are used as catalysts in the Suzuki reactions in an aqueous medium to investigate the effects of these stabilizers on the metallic nanoparticle catalytic activity and stability. The stability of the Pd nanoparticles is measured by the tendency of the nanoparticles to give Pd black powder after the catalytic reaction. The Suzuki reaction is a good “acid test” for examining the stability of these nanop...
417 citations
TL;DR: In this article, atom transfer radical polymerization (ATRP) was applied to the synthesis of amphiphilic cylindrical polymer brushes by using the "grafting from" technique.
Abstract: Atom transfer radical polymerization (ATRP) was applied to the synthesis of amphiphilic cylindrical polymer brushes by using the “grafting from” technique The procedure included the following steps: (1) ATRP of 2-hydroxyethyl methacrylate (HEMA) gave well-defined poly(HEMA), (2) subsequent esterification of the pendant hydroxy groups of poly(HEMA) with 2-bromoisobutyryl bromide yielded a polyinitiator, poly(2-(2-bromoisobutyryloxy)ethyl methacrylate (PBIEM), (3) ATRP of various monomers (tert-butyl acrylate, or styrene) using PBIEM as polyinitiator yielded cylindrical brushes with homopolymer side chains, (4) addition of a second monomer (styrene or tert-butyl acrylate) formed the cylindrical brushes with diblock copolymer side chains (core−shell cylinders), and (5) hydrolysis of the poly(tert-butyl acrylate) (PtBA) block of the side chains to poly(acrylic acid) (PAA) formed amphiphilic core−shell polymer brushes By using this technique, well-defined core−shell cylindrical polymer brushes with polystyr
400 citations
TL;DR: In this article, the molecular weights of the resulting polymers were characterized by gel permeation chromatography (GPC) using refractive index and multiangle light scattering detection, confirming the synthesis of well-defined copolymer brushes.
Abstract: Brush macromolecules having poly(n-butyl acrylate-block-styrene) and poly(styrene-block-n-butyl acrylate) side chains have been synthesized by the “grafting from” approach using atom transfer radical polymerization (ATRP). The molecular weights of the resulting polymers were characterized by gel permeation chromatography (GPC) using refractive index and multiangle light scattering detection. The block copolymer side chains were cleaved from the backbone and analyzed by GPC, confirming the synthesis of well-defined copolymer brushes. Visualization of individual molecules by atomic force microscopy (AFM) enabled analysis of the conformation and microstructure of the brush macromolecules on mica surface. The brushes with the pnBuA core were almost fully stretched, while the inverted structure with the pS core exhibited longitudinal contraction compared to the contour length of the main chain. In addition, the poly(n-butyl acrylate-block-styrene) brushes demonstrated a characteristic necklace morphology which...
372 citations
359 citations
TL;DR: This study shows that highly cross-linked dimethacrylate systems, such as bis-GMA/TEGDMA, exhibit similar network structure and properties as a function of double bond conversion, regardless of the method or rate of cure.
348 citations
TL;DR: In this paper, a simple preparation method for single monodisperse CdS nanoparticles with controllable size and stability against oxidation is presented, where double-hydrophilic block copolymers consisting of a solvating poly(ethylene glycol) PEG block and a poly(polyethylene imine) PEI binding block have been used as effective stabilizers for the solution synthesis of high-quality CdC nanoparticles.
Abstract: A novel and simple preparation method for single monodisperse CdS nanoparticles with controllable size and stability against oxidation is presented. Double-hydrophilic block copolymers consisting of a solvating poly(ethylene glycol) PEG block and a poly(ethylene imine) PEI binding block have been used as effective stabilizers for the solution synthesis of high-quality CdS nanoparticles in water and methanol. Absorption, fluorescence spectroscopy, and transmission electron microscopy were employed for characterization, which revealed that the prepared CdS nanoparticles had a well-resolved cubic structure and were monodisperse in size. It was also found that the CdS nanoparticles were dispersed in solution as single entities and showed a very good resistance against oxidation for months, according to their polymer shell. The particle size was controllable in the range between 2 and 4 nm by adjusting the polymer concentration and choice of the solvent.
TL;DR: The PEBAX® copolymer exhibits a different gas permeation behavior from that of homopolymers as mentioned in this paper, as the amount of impermeable regions in the block copolymers increases, the flow paths for the gas diffusion are restricted.
TL;DR: The hydrodynamic radius of the PLA−PEG 2:5−30:5 nanoparticles was solely dependent on the copolymer architecture and scaled linearly as NPLA1/3, wh...
Abstract: Nanoparticles assembled from poly(d,l-lactic acid)−poly(ethylene glycol) (PLA−PEG) block copolymers may have a therapeutic application in site-specific drug delivery. A series of AB block copolymers based on a fixed PEG block (5 kDa) and a varying PLA segment (2−110 kDa) have been synthesized by the ring-opening polymerization of d,l-lactide using stannous octoate as a catalyst. These copolymers assembled to form spherical nanoparticles in aqueous media following precipitation from a water-miscible organic solvent. 1H NMR studies of the PLA−PEG nanoparticles in D2O confirmed their core−shell structure, with negligible penetration of the hydrated PEG chains into the PLA core. The influence of the PLA block molecular weight on the hydrodynamic size and micellar aggregation number of the assemblies was determined by dynamic and static light scattering techniques. The hydrodynamic radius of the PLA−PEG 2:5−30:5 nanoparticles was solely dependent on the copolymer architecture and scaled linearly as NPLA1/3, wh...
Patent•
12 Apr 2001
TL;DR: In this paper, a uniform distribution of both tacticity and comonomer between copolymer chains is described, and the copolymers exhibit a statistically insignificant intramolecular difference of tacticity.
Abstract: Ethylene propylene copolymers, substantially free of diene, are described. The copolymers will have a uniform distribution of both tacticity and comonomer between copolymer chains. Further, the copolymers will exhibit a statistically insignificant intramolecular difference of tacticity. The copolymers are made in the presence of a metallocene catalyst.
IBM1
TL;DR: The determination of the solid-state PL spectra and quantum efficiencies showed that there is an apparent optimum size of the dendritic side groups with the [G-2]-derivatives showing high reactivity with associated site isolation of the conjugated chain.
Abstract: The synthesis and characterization of complex dendritic, rigid rod poly-2,7-fluorene homopolymers and copolymers via a macromonomer approach is reported. Several 2,7-dibromofluorene monomers contai...
TL;DR: In this paper, the authors reported the ferroelectric and electromechanical properties of poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluorethylene) terpolymer, which exhibits a slim polarization hysteresis loop and a high electrostrictive strain at room temperature.
Abstract: This letter reports the ferroelectric and electromechanical properties of a class of ferroelectric polymer, poly(vinylidene-fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymer, which exhibits a slim polarizationhysteresis loop and a high electrostrictive strain at room temperature. The dielectric and polarization behaviors of this terpolymer are typical of the ferroelectric relaxor. The x-ray and Fourier transform infrared results reveal that the random incorporation of bulky chlorotrifluoroethylene (CTFE) ter-monomers into polymer chains causes disordering of the ferroelectric phase. Furthermore, CTFE also acts as random defect fields which randomize the inter- and intrachain polar coupling, resulting in the observed ferroelectric relaxor behavior.
TL;DR: In this article, the glass transition temperature of polystyrene thin films was investigated by measuring the change in the thermal expansion using X-ray reflectivity, and it was shown that the Tg of poly styrene is strongly dependent on the interactions between the polymer and the underlying substrate.
Abstract: Previous studies had demonstrated that the Tg of polymer thin films is strongly dependent on the interactions, γs, between the polymer and the underlying substrate. We present a study of the glass transition temperature, Tg, in thin films of polystyrene, PS, as a function of film thickness and as a function of γs by measuring the change in the thermal expansion using X-ray reflectivity. The Tg for PS on native silicon oxide was found to decrease with decreasing film thickness, consistent with results by others. Using random copolymers of styrene and methyl methacrylate anchored to the substrate, γs could be varied by changing the styrene fraction, f. With a constant PS film thickness of 330 A, the Tg was depressed by ∼20 °C as f was decreased from 1 to 0.75. An analysis analogous to the Gibbs−Thompson model indicated that the surface energy was not a suitable parameter to use to describe the effects of interfacial interactions on the Tg of polymer thin films. An associated local fractional change in the s...
TL;DR: In this paper, the carbazole units were copolymerized to introduce disorder in the polymer backbone, which improved the luminescence of polyfluorene polymers.
Abstract: To decrease aggregation phenomena and improve the luminescence of the blue-light-emitting polymer polyfluorene, carbazole units were copolymerized to introduce disorder in the polymer backbone. A “kink” linkage was introduced into the polyfluorene chain by forming a 9:1 and 7:3 copolymer with the carbazole group at the 3,6 positions. The disordered polyfluorene was made though a Ni-catalyzed reaction, which resulted in high yield and high molecular weight polymers. The structure and physical properties were confirmed by NMR, SEC, UV absorption, photoluminescence, elemental analysis, and quantum yield measurements. The copolymers exhibited better spectral properties both in solution and in film compared to previously synthesized polyfluorene homopolymers. Annealing studies showed both improved thermal and UV stability of the copolymer over previously reported homopolymers. Cyclic voltammetry studies showed a slightly lower highest occupied molecular orbital (HOMO) than the homopolymer.
TL;DR: In this article, a biphenol-based wholly aromatic poly (arylene ether sulfones) containing pendant sulfonate groups was prepared by direct aromatic nucleophilic substitution polycondensation of disodium 3,3'-disulfonate-4,4'-dichlorodiphenyl sulfone (SDCDPS), 4, 4'-diclodorodorophenylsulfone (DCDPS) and biphenols.
Abstract: Novel biphenol-based wholly aromatic poly (arylene ether sulfones) containing pendant sulfonate groups were prepared by direct aromatic nucleophilic substitution polycondensation of disodium 3,3'-disulfonate-4,4'-dichlorodiphenyl sulfone (SDCDPS), 4,4'-dichlorodiphenylsulfone (DCDPS) and biphenol. Copolymerization proceeded quantitatively to high molecular weight in N-methyl-2-pyrrolidinone at 190°C in the presence of anhydrous potassium carbonate. Tough membranes were successfully cast from the control and the copolymers, which had a SDCDPS/DCDPS mole ratio of either 40:60 or 60:40 using N,N-dimethylactamide; the 100% SDCDPS homopolymer was water soluble. Short-term aging (30 min) indicates that the desired acid form membranes are stable to 220°C in air and conductivity values at 25°C of 0.110 (40%) and 0.170 S/cm (60%) were measured, which are comparable to or higher than the state-of-the art fluorinated copolymer Nafion 1135 control. The new copolymers, which contain ion conductivity sites on deactivated rings, are candidates as new polymeric electrolyte materials for proton exchange membrane (PEM) fuel cells. Further research comparing their membrane behavior to post-sulfonated systems is in progress.
TL;DR: In this paper, the micellization of an EO-propylene oxide (PEO-PPO-PEO) symmetrical triblock copolymer (Pluronic®) F127 (EO 99 PO 65 EO 99, mol. wt. PPO=1750, %PEO=70) in aqueous solution in the presence of various additives (i.e., sodium chloride, urea and sodium dodecyl sulfate (SDS)) is examined by cloud point, surface tension, dye spectral change, sound velocity, viscos
TL;DR: Two micellar states are possible for a novel PPO-PDEA diblock copolymer synthesized by atom-transfer radical polymerization.
Abstract: Two micellar states are possible for a novel PPO-PDEA diblock copolymer synthesized by atom-transfer radical polymerization. Subtle variation of the solution pH value and temperature is all that is needed to form both conventional micelles (with the PDEA block in the core) and reverse micelles (with the PPO block in the core) in aqueous media (shown schematically). DEA=2-(diethylamino)ethyl methacrylate, PO=propylene oxide.
TL;DR: In this paper, a donor-acceptor diblock copolymer with continuous and nanometre-scale interpenetrating phases of electron donor and acceptor components is designed to be an efficient photovoltaic material.
TL;DR: The modified capsules offer many possibilities for novel applications as containers for controlled precipitation, as nanoreactors for catalyzed reactions, or as sensors.
Abstract: Hollow polyelectrolyte capsules in micro- and submicrometer size were prepared. Their interior was functionalized by a “ship in bottle” synthesis of copolymers. While the monomers permeated the cap...
TL;DR: In this article, the BAB-type triblock copolymers composed of a central poly(ethyelene oxide) (PEO, M nPEO = 1000) block and two poly[(D,L-lactic acid)-co-(glycolic acid)] end blocks with molecular weights between 900 and 1 600 exhibited an intersting phase transition behavior.
Abstract: The BAB-type triblock copolymers composed of a central poly(ethyelene oxide) (PEO, M nPEO = 1000) block and two poly[(D,L-lactic acid)-co-(glycolic acid)] end blocks with molecular weights between 900 and 1 600 exhibited an intersting phase transition behavior. The copolymer aqueous solution can form micelles with PLGA loops in the core and a PEO shell and groups of micelles because of bridging between micelles caused by the PLGA blocks with raising temperature. A possible micellar gelation mechanism was suggested.
TL;DR: Surprisingly, the proteins remain functional despite the extreme thickness of the membranes and that even after polymerization of the reactive triblock copolymers, which opens a new field to create mechanically stable protein/polymer hybrid membranes.
Abstract: Self-assembly of an amphiphilic triblock copolymer carrying polymerizable end-groups is used to prepare nanometer-sized vesicular structures in aqueous solution. The triblock copolymer shells of the vesicles can be regarded as a mimetic of biological membranes although they are 2 to 3 times thicker than a conventional lipid bilayer. Nevertheless, they can serve as a matrix for membrane-spanning proteins. Surprisingly, the proteins remain functional despite the extreme thickness of the membranes and that even after polymerization of the reactive triblock copolymers. This opens a new field to create mechanically stable protein/polymer hybrid membranes. As a representative example we functionalize (polymerized) triblock copolymer vesicles by reconstituting a channel-forming protein from the outer cell wall of Gram-negative bacteria. The protein used (OmpF) acts as a size-selective filter, which allows only for passage of molecules with a molecular weight below 400 g mol-1. Therefore substrates may still have access to enzymes encapsulated in such protein/polymer hybrid nanocontainers. We demonstrate this using the enzyme β-lactamase which is able to hydrolyze the antibiotic ampicillin. In addition, a transmembrane voltage above a given threshold causes a reversible gating transition of OmpF. This can be used to reversibly activate or deactivate the resulting nanoreactors.
TL;DR: In this article, two methods for self-assembly of the initiator monolayer were compared: one was to treat the silicon surface with 6-((2-bromo-2-methyl)propionyloxy)hexyltrichlorosilane solution (solution method), and the other was to treatment it with the vapor of 3-aminopropyl)triethoxysilane, followed by amidization with 2-branchoisobutyric acid (vapor method).
Abstract: Homopolymer and block amphiphilic polymer brushes on silicon wafers have been successfully prepared by combining the self-assembled monolayer of initiator and atom transfer radical polymerization (ATRP). Two methods for self-assembly of initiator monolayer were compared: One was to treat the silicon surface with 6-((2-bromo-2-methyl)propionyloxy)hexyltrichlorosilane solution (solution method), and the other was to treat it with the vapor of 3-aminopropyl)triethoxysilane, followed by amidization with 2-bromoisobutyric acid (vapor method). While the solution method produced particles due to cross-linked products of the chlorosilane on silicon surface, the vapor method gave a uniform surface. The homopolymer brushes of poly(methyl methacrylate) (PMMA) and poly(acrylamide) (PAAM) were prepared by ATRP on the modified silicon wafer by the initiator. The amphiphilic block copolymer brushes consisting of PAAM and PMMA blocks were obtained by using the homopolymer brush as the macroinitiator for the second ATRP ...
TL;DR: Very low polydispersity spherical micelles are observed that consist of a PS core surrounded by a pH-sensitive P2VP shell and a corona of PEO chains end-capped by a hydroxyl group.
Abstract: A reactor for the synthesis of gold nanoparticles (see atomic force microscopy image) is one of the uses of a poly(styrene)-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) triblock copolymer (PS-b-P2VP-b-PEO) which forms core-shell-corona micelles in water. Very low polydispersity spherical micelles are observed that consist of a PS core surrounded by a pH-sensitive P2VP shell and a corona of PEO chains end-capped by a hydroxyl group. The corona can act as a site for attaching responsive or sensing molecules.
TL;DR: In this paper, the authors report the design of new block copolymer electrolytes based on poly(methyl methacrylate), PMMA, and poly(oligo oxycthylene methacelate), POEM, which are segmentally mixed at elevated temperatures appropriate for melt processing, while exhibiting a mierophase separated morphology at ambient temperature.
Abstract: Microphase separated block copolymers consisting of an amorphous poly(ethylene oxide) (PEO)-based polymer covalently bound to a second polymer offer a highly attractive avenue to achieving both dimensional stability and high ionic conductivity in polymer electrolytes for solid-state rechargeable lithium batteries. However, due to the strong thermodynamic incompatibility typically found for most polymer pairs, the disordered, liquid state of the copolymer can rarely he achieved without the incorporation of a solyent, which complicates processing, Herein, we report the design of new block copolymer electrolytes based on poly(methyl methacrylate), PMMA, and poly(oligo oxycthylene methacrylate), POEM, which are segmentally mixed at elevated temperatures appropriate for melt processing, while exhibiting a mierophase separated (ordered) morphology at ambient temperature. Although pure PMMA-b-POEM is segmentally mixed at all temperatures, it is shown that mierophase separation in these materials can be induced in a controlled manner by the incorporation of even limited amounts of lithium trifluoromethane sulfonate (LiCF 3 SO 3 ), a salt commonly employed to render PEO ionically conductive. Such salt-induced microphase separation suggests a simple method for designing new solid polymer electrolytes combining high ionic conductivities with excellent dimensional stability and improved processing flexibility.
TL;DR: In this article, a novel wet chemical approach is reported for the facile synthesis of silver nanowires with diameters in the range of 20−40 nm in aqueous solutions of a double-hydrophilic block copolymer (DHBC) PEO-b-PMAA.
Abstract: A novel, wet chemical approach is reported for the facile synthesis of silver nanowires with diameters in the range of 20−40 nm in aqueous solutions of a double-hydrophilic block copolymer (DHBC) PEO-b-PMAA. Investigation of the time-dependent formation of the silver nanowires revealed that they were produced through a directed aggregation growth process and the formation of DHBC micelles could play an important role in nanowire formation.