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Diblock Copolymers (diblock + copolymer)
Kinds of Diblock Copolymers Terms modified by Diblock Copolymers Selected AbstractsMulti-Responsive Supramolecular Double Hydrophilic Diblock Copolymer Driven by Host-Guest Inclusion Complexation between , -Cyclodextrin and Adamantyl MoietiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2009Hao Liu Abstract Well-defined , -CD-terminated poly(N -isopropylacrylamide) (, - CD -PNIPAM) was synthesized via a combination of atom transfer radical polymerization (ATRP) and click chemistry. Moreover, adamantyl-terminated poly(2-(diethylamino)ethyl methacrylate) (Ad -PDEA) was synthesized by ATRP using an adamantane-containing initiator. Host-guest inclusion complexation between ,-CD and adamantyl moieties drives the formation of supramolecular double hydrophilic block copolymers (DHBC) from , -CD-PNIPAM and Ad -PDEA. The obtained supramolecular PNIPAM- b -PDEA diblock copolymer exhibits intriguing multi-responsive and reversible micelle-to-vesicle transition behavior in aqueous solution by dually playing with solution pH and temperatures. [source] Crystallization and Ring-Banded Spherulite Morphology of Poly(ethylene oxide)- block -Poly(, -caprolactone) Diblock CopolymerMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2004Shichun Jiang Abstract Summary: The crystallization behavior of crystalline-crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(, -caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring-banded spherulite morphology for the PEO- b -PCL diblock copolymer. DSC heating curve for the PEO- b -PCL block copolymer. [source] Fabrication of Regularly Patterned Microporous Films by Self-Organization of an Amphiphilic Liquid-Crystalline Diblock Copolymer in a Dry EnvironmentMACROMOLECULAR MATERIALS & ENGINEERING, Issue 1 2010Dong Chen Abstract An amphiphilic LCBC PEO -b- PAz consisting of flexible PEO as a hydrophilic block and poly(methacrylic acid) containing an azobenzene moiety in side chain as a hydrophobic LC segment was synthesized and used to fabricated microporous films by spin-coating method under a dry environment. With the help of a small amount of water, well-arranged ellipsoidal micropores embedded in a LC matrix were obtained and the pore size is in the range of several tens µm of water. The influence of water content and rotational speed was studied in detail. It was found that regularly patterned microporous films can be prepared with certain water content, and the pore size can be easily tailored through changing the rotational speed. The obtained microporous structures showed good thermal and photo stability. [source] Synthesis of Well-Defined Rod-Coil Diblock Copolymer of Aromatic Polyether and Polyacrylonitrile by Chain-Growth Condensation Polymerization and Atom Transfer Radical PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2008Naomi Ajioka Abstract The synthesis of diblock copolymers of aromatic polyether and polyacrylonitrile (PAN) was conducted by chain-growth condensation polymerization (CGCP) and atom transfer radical polymerization (ATRP) from an orthogonal initiator. When CGCP for aromatic polyether was carried out from a PAN macroinitiator obtained by ATRP with an orthogonal initiator, decomposition of the PAN backbone occurred. However, when ATRP of acrylonitrile was conducted from an aromatic polyether macroinitiator obtained by CGCP followed by introduction of an ATRP initiator unit, the polymerization proceeded in a well-controlled manner to yield aromatic polyether- block -polyacrylonitrile (polyether- b -PAN) with low polydispersity. This block copolymer self-assembled in N,N -dimethylformamide to form bundle-like or spherical aggregates, depending on the length of the PAN units in the block copolymer. [source] Mesophase Separation of Diblock Copolymer Confined in a Cylindrical Tube Studied by Dissipative Particle DynamicsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006Jian Feng Abstract Summary: The morphologies of diblock copolymers confined in a cylindrical tube have been investigated by the dissipative particle dynamics (DPD) method. Results indicate that the morphology depends on the volume ratio of the immiscible blocks, the diameter of the cylindrical tube and the interactions between the blocks and between the confinement wall and blocks. For symmetric diblock copolymers, when the tube wall is uniform toward the two blocks, perpendicular lamellae or a stacked disk morphology are generally formed except when the diameter of the cylindrical tube is very small; in that case, a special bi-helix morphology forms because of the entropy effect. When the tube wall is non-uniform, as the diameter of the tube increases, perpendicular lamellae are first formed, then changing to parallel lamellae and, finally, back to perpendicular lamellae again. An intermediate morphology characterizing the transition between perpendicular and parallel lamellae is observed. If the non-uniformity of the wall is further enhanced, only parallel lamellae can be found. In the case of asymmetric diblock copolymers, more complex morphologies can be obtained. Multi-cylindrical micro-domains and a multilayer helical phase as well as other complex pictures are observed. Generally, the morphologies obtained could find their counterparts from experiments or Monte Carlo simulations; however, differences do exist, especially in some cases of asymmetric diblock copolymers. Bi-helix and stacked disks morphologies of A5B5 diblock copolymer confined in two different neutral nanocylinders. [source] Self-Supporting, Double Stimuli-Responsive Porous Membranes From Polystyrene- block -poly(N,N -dimethylaminoethyl methacrylate) Diblock CopolymersADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Felix Schacher Abstract Asymmetric membranes are prepared via the non-solvent-induced phase separation (NIPS) process from a polystyrene- block -poly(N,N -dimethylaminoethyl methacrylate) (PS- b -PDMAEMA) block copolymer. The polymer is prepared via sequential living anionic polymerization. Membrane surface and volume structures are characterized by scanning electron microscopy. Due to their asymmetric character, resulting in a thin separation layer with pores below 100,nm on top and a macroporous volume structure, the membranes are self-supporting. Furthermore, they exhibit a defect-free surface over several 100,µm2. Polystyrene serves as the membrane matrix, whereas the pH- and temperature-sensitive minority block, PDMAEMA, renders the material double stimuli-responsive. Therefore, in terms of water flux, the membranes are able to react on two independently applicable stimuli, pH and temperature. Compared to the conditions where the lowest water flux is obtained, low temperature and pH, activation of both triggers results in a seven-fold permeability increase. The pore size distribution and the separation properties of the obtained membranes were tested through the pH-dependent filtration of silica particles with sizes of 12,100,nm. [source] Synthesis of Inorganic,Organic Diblock Copolymers as a Precursor of Ordered Mesoporous SiCN Ceramic,ADVANCED MATERIALS, Issue 17 2007D. Nghiem A novel poly(vinyl)silazane- block -polystyrene diblock copolymer is successfully synthesized by living free-radical polymerization via a reversible addition fragmentation chain transfer (RAFT) route (see figure). The obtained diblock copolymer, having an inorganic volume fraction of 0.69, leads to phase-separation at the nanoscale to form an ordered nanostructure, which is converted to well-ordered mesoporous SiCN ceramic after heating at 800,°C and maintained up to 1400,°C. [source] Synthesis of Well-Defined Statistical and Diblock Copolymers of Acrylamide and Acrylic Acid by Inverse Miniemulsion Raft PolymerizationMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2010Liu Ouyang Abstract Well-defined statistical and diblock copolymers with acrylamide and acrylic acid were synthesized by inverse miniemulsion RAFT polymerization. Statistical copolymers with various composition ratios were synthesized. Compositional drift was observed during polymerization. Acrylamide was polymerized with a water-soluble initiator (VA-044) at 60,°C to give the RAFT-agent-containing acrylamide homopolymer with a narrow molecular-weight distribution (PDI,<,1.3), which was then chain-extended with acrylic acid to obtain the diblock copolymer. [source] Janus Micelle Formation Induced by Protonation/Deprotonation of Poly(2-vinylpyridine) -block- Poly(ethylene oxide) Diblock CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3 2010Xue Li Abstract A novel approach to amphiphilic polymeric Janus micelles based on the protonation/deprotonation process of poly(2-vinylpyridine) -block- poly(ethylene oxide) (P2VP -b- PEO) diblock copolymers in THF is presented. It is found that addition of HCl to the micelles solution of P2VP -b- PEO copolymers leads to the formation of vesicles. Subsequently mixing a small amount of hydrazine monohydrate with the vesicle solution can induce the dissociation and reorganization of the vesicles into Janus micelles. When HCl is replaced by HAuCl4 precursors, composite Janus particles containing gold in P2VP blocks are obtained. [source] Micellar Structures of Hydrophilic/Lipophilic and Hydrophilic/Fluorophilic Poly(2-oxazoline) Diblock Copolymers in WaterMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2008Ruzha Ivanova Abstract Amphiphilic poly(2-alkyl-2-oxazoline) diblock copolymers of 2-methyl-2-oxazoline (MOx) building the hydrophilic block and either 2-nonyl-2-oxazoline (NOx) for the hydrophobic or 2-(1H,1H,,2H,2H,-perfluorohexyl)-2-oxazoline (FOx) for the fluorophilic block were synthesized by sequential living cationic polymerization. The polymer amphiphiles form core/shell micelles in aqueous solution as evidenced using small-angle neutron scattering (SANS). Whereas the diblock copolymer micelles with a hydrophobic NOxn block are spherical, the micelles with the fluorophilic FOxn are slightly elongated, as observed by SANS and TEM. In water, the micelles with fluorophilic and lipophilic cores do not mix, but coexist. [source] Two-Dimensional Chromatography of Complex Polymers, 7 , Detailed Study of Polystyrene- block -Polyisoprene Diblock Copolymers Prepared by Sequential Anionic Polymerization and Coupling ChemistryMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19 2008Valentina Mass Abstract Two-dimensional chromatographic methods were developed using LC-CC in the first and SEC in the second dimension. These methods were applied for the investigation of PS- b -PI diblock copolymers synthesized by different approaches: sequential living anionic polymerization and coupling of living precursor blocks. The first dimension separates according to the individual block length of PS or PI blocks, whereas the second dimension separates with respect to the total molar masses of components. 2D-LC analysis provides information on the purity of the reaction products, the presence of by-products, the chemical compositions and the molar masses of all product components. The accuracy and selectivity of 2D-LC is discussed. [source] RAFT Synthesis and Solution Properties of pH-Responsive Styrenic-Based AB Diblock Copolymers of 4-Vinylbenzyltrimethylphosphonium Chloride with N,N -DimethylbenzylvinylamineMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2007Andrew B. Lowe Abstract The RAFT synthesis and solution properties of AB block copolymers of 4-vinylbenzyltrimethylphosphonium chloride (TMP) and N,N -dimethylbenzylvinylamine (DMBVA) is described. The pH-dependent self-assembly properties of the AB diblock copolymers were examined using of 1H NMR, DLS, and fluorescence spectroscopy. The size of the polymeric aggregates depends on the block copolymer composition/molecular mass. The self assembly is completely reversible, as predicted from the tunable hydrophilicity/hydrophobicity of the DMBVA residues. The AB diblock copolymers can be effectively locked in the self-assembled state using a straightforward core crosslinking reaction between the tertiary amine residues of DMBVA and difunctional 1,4-bis(bromomethyl)benzene. [source] Synthesis of PLLA-MPEG Diblock Copolymers by Microwave-Assisted Copolymerization of L -Lactide and Methoxy Poly(ethylene glycol)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2007Chao Zhang Abstract PLLA-MPEG diblock copolymers with a controlled number-average molar mass ranging from 7,330 to 117,610 g,·,mol,1 and an L -lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100,°C by MPEG-initiated ROP of L -lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA-MPEG diblock copolymers with longer PLLA segments. [source] N -Isopropylacrylamide/2-Hydroxyethyl Methacrylate Star Diblock Copolymers: Synthesis and Thermoresponsive BehaviorMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2006Zhiqiang Cao Abstract Summary: Tri-arm star diblock copolymers, poly(2-hydroxyethyl methacrylate)- block -poly(N -isopropylacrylamide) [P(HEMA- b -NIPAAm)] with PHEMA and PNIPAAm as separate inner and outer blocks were synthesized via a two-step ATRP at room temperature. The formation, molecular weight and distribution of polymers were examined, and the kinetics of the reaction was monitored. The PDI of PHEMA was shown to be lower, indicating well-controlled polymerization of trifunctional macro-initiator and resultant star copolymers. The thermoresponsive behavior of diblock copolymer aqueous solution were studied by DSC, phase diagrams, temperature-variable 1H NMR, TEM and DLS. The results revealed that introducing a higher ratio of HEMA into copolymers could facilitate the formation of micelles and the occurrence of phase transition at lower temperatures. TEM images showed that I-(HEMA40 -NIPAAm320)3 solutions developed into core-shell micelles with diameters of approximately 100 nm. I-(HEMA40 -NIPAAm320)3 was used as a representative example to elucidate the mechanism underlying temperature-induced phase transition of copolymer solution. In this study we proposed a three-stage transition process: (1) separately dispersed micelles state at ,17,22,°C; (2) aggregation and fusion of micelles at ,22,29,°C; (3) sol-gel transition of PNIPAAm segments at ,29,35,°C, and serious syneresis of shell layers. Molecular architecture of Poly(HEMA- b -NIPAAm). [source] Melt Structure and its Transformation by Sequential Crystallization of the Two Blocks within Poly(L -lactide)- block -Poly(, -caprolactone) Double Crystalline Diblock CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2006I. W. Hamley Abstract Summary: Sequential crystallization of poly(L -lactide) (PLLA) followed by poly(, -caprolactone) (PCL) in double crystalline PLLA- b -PCL diblock copolymers is studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). Three samples with different compositions are studied. The sample with the shortest PLLA block (32 wt.-% PLLA) crystallizes from a homogeneous melt, the other two (with 44 and 60% PLLA) from microphase separated structures. The microphase structure of the melt is changed as PLLA crystallizes at 122,°C (a temperature at which the PCL block is molten) forming spherulites regardless of composition, even with 32% PLLA. SAXS indicates that a lamellar structure with a different periodicity than that obtained in the melt forms (for melt segregated samples). Where PCL is the majority block, PCL crystallization at 42,°C following PLLA crystallization leads to rearrangement of the lamellar structure, as observed by SAXS, possibly due to local melting at the interphases between domains. POM results showed that PCL crystallizes within previously formed PLLA spherulites. WAXS data indicate that the PLLA unit cell is modified by crystallization of PCL, at least for the two majority PCL samples. The PCL minority sample did not crystallize at 42,°C (well below the PCL homopolymer crystallization temperature), pointing to the influence of pre-crystallization of PLLA on PCL crystallization, although it did crystallize at lower temperature. Crystallization kinetics were examined by DSC and WAXS, with good agreement in general. The crystallization rate of PLLA decreased with increase in PCL content in the copolymers. The crystallization rate of PCL decreased with increasing PLLA content. The Avrami exponents were in general depressed for both components in the block copolymers compared to the parent homopolymers. Polarized optical micrographs during isothermal crystallization of (a) homo-PLLA, (b) homo-PCL, (c) and (d) block copolymer after 30 min at 122,°C and after 15 min at 42,°C. [source] Defined Poly[styrene- block -(ferrocenylmethyl methacrylate)] Diblock Copolymers via Living Anionic PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2009Markus Gallei Abstract Ferrocenylmethyl methacrylate (FMMA) is one of the very few metallocene-based monomers that are promising candidates for truly living anionic polymerization. Nevertheless, FMMA homopolymers with a narrow polydispersity, or block copolymerization studies that result in satisfying blocking efficiencies, are unknown so far. Here we describe a procedure that leads to highly regular FMMA-based polymers for the first time, characterized by polydispersity indices (PDI) of less that 1.05 and very high blocking efficiencies (>95%) in sequential copolymerization with styrene. Some of the obtained poly[styrene- block -(ferrocenylmethyl methacrylate)]s show unusual microphase morphologies, presumably the consequence of high Tgs causing ,frustrated' non-equilibrium states. [source] Polymer Crystallization Influenced by Initial Orientation of Cylindrical Diblock Copolymers in Thin FilmsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 19 2008Ping Yang Abstract The effect of the initial states (disordered perpendicular cylinder structure vs. parallel cylinder structure) on the crystallization of polystyrene- block -poly(ethylene oxide) (PS- b -PEO) thin films during cyclohexane annealing was investigated. The cylindrical domains perpendicular or parallel to the surface were obtained by controlling the film thickness. During solvent annealing, for the film with the perpendicular cylinders, the ordering degree of cylinders was increased. The enthalpic increase is large enough for the forming of square-shaped crystals, and subsequently the square-shaped single crystals surrounded by the ordered hexagonally packed perpendicular cylinders evolved to the dendrite ones. For the film with the parallel cylinders, the parallel cylinders were translated to the perpendicular ones. The increased enthalpy was not large enough for the formation of square-shaped single crystals. Instead, the dendrite-like crystals started at the edge of terraces. [source] Novel Structured Composites Formed from Gold Nanoparticles and Diblock CopolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 12 2007Xi Chen Abstract We report a simple procedure to prepare a novel Au-micelle composite with a core-shell-corona structure. This composite is prepared by reduction of tetrachloroauric acid (HAuCl4,·,3H2O) in dilute aqueous solution containing polystyrene- block -poly(4-vinylpyridine) micelles and poly(ethylene oxide)- block -poly(4-vinylpyridine) copolymers. The micelles with a polystyrene core and a poly(4-vinylpyridine) shell are transformed into Au-micelle composites with a polystyrene core, a swollen hybrid Au/poly(4-vinylpyridine) inner shell, and a poly(ethylene oxide) corona by direct physisorption of gold particles with poly(4-vinylpyridine) chains. [source] Photoinduced Fusion of Micro-Vesicles Self-Assembled from Azobenzene-Containing Amphiphilic Diblock CopolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 11 2007Wei Su Abstract Poly(N -isopropylacrylamide)- block -poly{6-[4-(4-methylphenyl-azo) phenoxy] hexylacrylate} (PNIPAM- b -PAzoM) was synthesized by successive reversible addition-fragmentation chain transfer (RAFT) polymerization. In H2O/THF mixture, amphiphilic PNIPAM- b -PAzoM self-assembles into giant micro-vesicles. Upon irradiation of light at 365 nm, fusion of the vesicles was observed directly under an optical microscope. The real-time fusion process is presented and the derivation is preliminarily due to the perturbation by the photoinduced trans -to- cis isomerization of azobenzene units in the vesicles. [source] Synthesis and Characterization of Helix-Coil Diblock Copolymers with Controlled Supramolecular Architectures in Aqueous Solution,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2005Jie Zhang Abstract Summary: A series of helix-coil diblock copolymers based on poly(ethylene oxide) and optically active helical poly{(+)-2,5-bis[4,-((S)-2-methylbutoxy)phenyl]styrene} (PMBPS) were synthesized via atom transfer radical polymerization (ATRP). The synthetic methodology permitted straightforward preparation of the diblock copolymers with relatively low polydispersities and a broad range of compositions and molecular weights. Depending on the composing block length and the initial concentration, the copolymers self-assembled into different supramolecular structures in aqueous solution, including spherical micelles, vesicles, multilamellar vesicles, large compound vesicles, and tubules. Schematic representation of the synthesis of PEO- b -PMBPS block copolymers and their aggregation in aqueous solution. [source] The Formation of Biodegradable Polymeric Micelles from Newly Synthesized Poly(aspartic acid)- block -Polylactide AB-Type Diblock CopolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 6 2004Hidetoshi Arimura Abstract Summary: A poly(aspartic acid)- block -polylactide (PAsp- block -PLA) diblock copolymer was synthesized through the polymerization of , -benzyl- L -aspartate- N -carboxyanhydride [Asp(OBzl)-NCA] with amino-terminating polylactide (NH2 -PLA) as a macroinitiator. The chain length of the PAsp segment could be easily controlled by changing the monomer/initiator ratio. Dynamic light scattering measurements of PAsp- block -PLA aqueous solutions revealed the formation of polymeric micelles. Changes in the micelles as a function of pH were investigated. The structure and formation of micelles of the poly(aspartic acid)- block -polylactide (PAsp- block -PLA) diblock copolymers synthesized here. [source] Morphology of Symmetric Diblock Copolymers Confined Between Two Stripe-Patterned Surfaces , Tilted Lamellae and MoreMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2005Qiang Wang Abstract Summary: We report the first Monte Carlo simulations on the thin-film morphology of symmetric diblock copolymers confined between either symmetrically or antisymmetrically stripe-patterned surfaces. Under suitable surface configurations (where the lamellae can comply with the surface patterns and can have a period close to the bulk lamellar period L0), tilted lamellae are observed for film thicknesses D,,,2L0; the checkerboard morphology is obtained for smaller film thicknesses. The A-B interfaces in the tilted lamellae are basically perpendicular to the surfaces in their immediate vicinity, and exhibit undulations away from them. In some cases, the severe frustration imposed by the two patterned surfaces leads to irregular or unexpected morphologies, which represent locally stable states. The efficient sampling of our expanded grand-canonical Monte Carlo technique enables us to observe more than one locally stable morphologies and the flipping between them during a single simulation run. Tilted lamellae between symmetrically patterned surfaces (perpendicular to z) with a surface pattern period of 1.5L0 and a film thickness of 2.67L0. L0 is the bulk lamellar period and the black curves mark the A-B interfaces. [source] Modeling of the Phase Separation Behavior of Polydisperse Semi-Flexible Diblock CopolymersMACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2004Andreas John Abstract Summary: A modified random phase approximation method with a cumulant expansion for the semi-flexible structure factor of diblock copolymers was exercised to describe the phase separation behavior of semi-flexible and polydisperse diblock copolymers. Scattering curves and spinodal diagrams were calculated applying monomer specific input parameters. The influence of polydispersity was included applying basic concepts of mathematical statistics utilizing several probability density distributions in the case of the two single blocks. In contrast to semi-flexibility, the main effect of polydispersity was found to shift the spinodal up, thus to enlarge the range of existence of the homogeneous phase. Twofold Schultz-Zimm distribution of diblock copolymers. [source] Supramolecular Self-Assembly of Conjugated Diblock CopolymersCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2004Hengbin Wang Dr. Abstract This paper describes the synthesis and characterization of a novel series of copolymers with different lengths of oligo(phenylene vinylene) (OPV) as the rod block, and poly(propylene oxide) as the coil block. Detailed characterization by means of transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle neutron scattering (SANS) revealed the strong tendency of these copolymers to self-assemble into cylindrical micelles in solution and as-casted films on a nanometer scale. These micelles have a cylindrical OPV core surrounded by a poly(propylene glycol) (PPG) corona and readily align with each other to form parallel packed structures when mica is used as the substrate. A packing model has been proposed for these cylindrical micelles. [source] One-Pot Synthesis of Lactide,Styrene Diblock Copolymers via Catalytic Immortal Ring-Opening Polymerization of Lactide and Nitroxide-Mediated Polymerization of StyreneCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 5 2010Valentin Poirier Abstract An efficient, practical, and industrially relevant procedure for the production of polymer materials, in which a part of the oil-derived polyolefins has been replaced by a renewable, biodegradable, and biocompatible poly(lactide) block, is presented. Binary catalytic systems combining innocuous metals (yttrium, zinc, magnesium, or calcium) and bifunctional alcohols (acting as transfer agents) were developed to promote the immortal ring-opening polymerization of lactide directly in styrene. Up to 20,000,equivalents of lactide were polymerized (metal catalyst loading of 50,100,ppm) in a controlled fashion in the presence of 10,100,equivalents of a double-headed transfer agent to give as many end-functionalized poly(lactide) macromolecules that can be used eventually as macroinitiators for the controlled nitroxide-mediated polymerization of styrene. The specific use of the sterically shielded complex [BDI- iPr]Zn-N(SiMe3)2 ([BDI- iPr]=bis(diketiminate) ligand) allowed the efficient, catalytic, and controlled production of poly(lactide)- block -poly(styrene) materials in a one-pot, solvent-free sequential procedure, with nearly 100,% atom-efficiency. [source] Novel well-defined glycopolymers synthesized via the reversible addition fragmentation chain transfer process in aqueous mediaJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2009Zhicheng Deng Abstract We describe here the direct synthesis of novel gluconamidoalkyl methacrylamides by reacting D -gluconolactone with aminoalkyl methacrylamides. The glycomonomers were then successfully polymerized via the reversible addition-fragmentation chain transfer process (RAFT) using 4-cyanopentanoic acid dithiobenzoate (CTP) as chain transfer agent and 4,4,-azobis(4-cyanovaleric acid) (ACVA) as the initiator in aqueous media. Well-defined polymers were obtained as revealed by gel permeation chromatography. Diblock copolymers were then synthesized by the macro-CTA approach. The cationic glycopolymers were subsequently used in the formation of nanostructures via the complexation with plasmid DNA. As noted by dynamic light scattering, monodisperse nanoparticles were obtained via the electrostatic interaction of the cationic glycopolymer with DNA. The sizes of the nanoparticles formed were found to be stable and independent of pH. In vitro cell viability studies of the glycopolymers were carried out using HELA cell lines. The RAFT synthesized glycopolymers and cationic glyco-copolymers revealed to be nontoxic. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 614,627, 2009 [source] Diblock copolymers based on allyl methacrylate: Synthesis, characterization, and chemical modificationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2007Rodrigo París Abstract Different diblock copolymers constituted by one segment of a monomer supporting a reactive functional group, like allyl methacrylate (AMA), were synthesized by atom transfer radical polymerization (ATRP). Bromo-terminated polymers, like polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) were employed as macroinitiators to form the other blocks. Copolymerizations were carried out using copper chloride with N,N,N,,N,,N, -pentamethyldiethylenetriamine (PMDETA) as the catalyst system in benzonitrile solution at 70 °C. At the early stage, the ATRP copolymerizations yielded well-defined linear block copolymers. However, with the polymerization progress a change in the macromolecular architecture takes place due to the secondary reactions caused by the allylic groups, passing to a branched and/or star-shaped structure until finally yielding gel at monomer conversion around 40% or higher. The block copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy, and differential scanning calorimetry (DSC). In addition, one of these copolymers, specifically P(BA- b -AMA), was satisfactorily modified through osmylation reaction to obtain the subsequent amphiphilic diblock copolymer of P(BA- b -DHPMA), where DHPMA is 2,3-dihydroxypropyl methacrylate; demonstrating the feasibility of side-chain modification of the functional obtained copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3538,3549, 2007 [source] The Use of the RAFT-Technique for the Preparation of Temperature/pH Sensitive Polymers in Different ArchitecturesMACROMOLECULAR SYMPOSIA, Issue 1 2009Angel Licea-Claveríe Abstract In this contribution we report the use of the RAFT-technique for the preparation of three types of responsive polymeric materials with a high potential of application in the biomedical field: 1.-Diblock copolymers with reversible self-assembly capacity as a function of pH based on N,N, -diethylaminoethyl methacrylate (DEAEM) and 2-methacryloyloxy benzoic acid (MAOB); 2.-Diblock copolymers with reversible self-assembly capacity as a function of temperature, based N -isopropylacrylamide (NIPAAm) and n-hexyl acrylate (HA); and 3.-Polymeric stars with random number of arms consisting either in NIPAAm-arms or copolymeric NIPAAm-arms and hydrophobic core. [source] Synthesis of poly(N, N -dimethylacrylamide)- block -poly(ethylene oxide)- block -poly(N, N -dimethylacrylamide) and its application for separation of proteins by capillary zone electrophoresisELECTROPHORESIS, Issue 10 2010Jing Xu Abstract A series of well-defined triblock copolymers, poly(N, N -dimethylacrylamide)- block -poly(ethylene oxide)- block -poly(N, N -dimethylacrylamide) (PDMA- b -PEO- b -PDMA) synthesized by atom transfer radical polymerization, were used as physical coatings for protein separation. A comparative study of EOF showed that the triblock copolymer presented good capillary coating ability and EOF efficient suppression. The effects of the Mr of PDMA block in PDMA- b -PEO- b -PDMA triblock copolymer and buffer pH on the separation of basic protein for CE were investigated. Moreover, the influence of the copolymer structure on separation of basic protein was studied by comparing the performance of PDMA- b -PEO- b -PDMA triblock copolymer with PEO- b -PDMA diblock copolymer. Furthermore, the triblock copolymer coating showed higher separation efficiency and better migration time repeatability than fused-silica capillary when used in protein mixture separation and milk powder samples separation, respectively. The results demonstrated that the triblock copolymer coatings would have a wide application in the field of protein separation. [source] A Novel Biodegradable and Light-Breakable Diblock Copolymer Micelle for Drug Delivery,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Zhigang Xie A facile approach to the preparation of light-responsive copolymer micelles is developed. This approach is based on the attachment of hydrophobic groups to one block of a diblock copolymer via a light-sensitive linkage. The micelles can be dissociated under light irradiation and release the encapsulated pyrene. The obtained polymeric micelles are expected to be of use as drug-delivery vehicles. [source] | ||||||||||||||||||||||||||||