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Amphiphilic Diblock Copolymers (amphiphilic + diblock_copolymer)
Selected AbstractsPhotoinduced 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] Micellar structure of amphiphilic poly(2-oxazoline) diblock copolymersJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007C. M. Papadakis Amphiphilic diblock copolymers from poly(2-oxazoline)s in aqueous solution can form micelles. By means of small-angle neutron scattering, we have found that poly[(n -nonyl-2-oxazoline)- b -(methyl-2-oxazoline)] {P[(NOx)- b -(MOx)]} diblock copolymers in aqueous solution form micelles of core-shell type. We have determined the core radius and the shell thickness of the micelles. Comparing the values obtained to the stretched lengths of the blocks leads to the conclusion that the P(NOx) core blocks are stretched, whereas the P(MOx) shell blocks are coiled. [source] Environmentally responsive micelles from polystyrene,poly[bis(potassium carboxylatophenoxy)phosphazene] block copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2005Youngkyu Chang Abstract Amphiphilic diblock copolymers that contained hydrophilic poly[bis(potassium carboxylatophenoxy)phosphazene] segments and hydrophobic polystyrene sections were synthesized via the controlled cationic polymerization of Cl3PNSiMe3 with a polystyrenyl,phosphoranimine as a macromolecular terminator. These block copolymers self-associated in aqueous media to form micellar structures which were investigated by fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The size and shape of the micelles were not affected by the introduction of different monovalent cations (Li+, K+, Na+, and Cs+) into the stable micellar solutions. However, exposure to divalent cations induced intermicellar crosslinking through carboxylate groups, which caused precipitation of the ionically crosslinked aggregates from solution. This micelle-coupling behavior was reversible: the subsequent addition of monovalent cations caused the redispersion of the polystyrene- block -poly[bis(potassium carboxylatophenoxy)phosphazene] (PS,KPCPP) block copolymers into a stable micellar solution. Aqueous micellar solutions of PS,KPCPP copolymers also showed pH-dependent behavior. These attributes make PS,KPCPP block copolymers suitable for studies of guest retention and release in response to ion charge and pH. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2912,2920, 2005 [source] Behaviors of self-assembled diblock copolymer with pendant photosensitive azobenzene segmentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2010Jui-Hsiang Liu Abstract A novel monomer, ethyl 4-[4-(11-methacryloyloxyundecyloxy)phenyl azobenzoyl-oxyl] benzoate, containing a photoisomerizable NN group was synthesized. The monomer was further diblock copolymerized with methyl methacrylate. Amphiphilic diblock copolymer poly(methyl methacrylate- block -ethyl 4-[4-(11-methacryloyloxyundecyloxy)phenyl azobenzoyl-oxyl] benzoate (PMMA - b - PAzoMA) was synthesized using atom transfer radical polymerization. The reverse micelles with spherical construction were obtained with 2 wt % of the diblock copolymer in a THF/H2O mixture of 1:2. Under alternating UV and visible light illumination, reversible changes in micellar structure between sphere and rod-like particles took place as a result of the reversible E-Z photoisomerization of azobenzene segments in PMMA - b - PAzoMA. Microphase separation of the amphiphilic diblock copolymer in thin films was achieved through thermal and solvent aligning methods. The microphases of the annealed thin films were investigated using atom force microscopy topology and scanning electron microscopy analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1142,1148, 2010 [source] Synthesis of azobenzene-containing polymers via RAFT polymerization and investigation on intense fluorescence from aggregates of azobenzene-containing amphiphilic diblock copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2008Jie Xu Abstract The well-defined azobenzene-containing homopolymers, poly{6-(4-phenylazophenoxy)hexyl methacrylate (AHMA)} (PAHMA), were synthesized via reversible addition fragmentation chain transfer polymerization (RAFT) in anisole solution using 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the RAFT agent and 2,2,-azobisisobutyronitrile (AIBN) as the initiator. The first-order kinetic plot of the polymerization and the linear dependence of molecular weights of the homopolymers with the relatively low polydispersity index values (PDIs , 1.25) on the monomer conversions were observed. Furthermore, the amphiphilic diblock copolymer, poly{6-(4-phenylazophenoxy)hexyl methacrylate (AHMA)}- b -poly{2-(dimethylamino)ethyl methacrylate (DMAEMA)} (PAHMA- b -PDMAEMA), was prepared with the obtained PAHMA as the macro-RAFT agent. The structures and properties of the polymers were characterized by 1H NMR and GPC, respectively. Interestingly, the amphiphilic diblock copolymers in chloroform (CHCl3) solution (PAHMA23 - b -PDMAEMA97 (4 × 10,5 M, Mn(GPC) = 18,400 g/mol, PDI = 1.48) and PAHMA28 - b -PDMAEMA117 (6 × 10,5 M, Mn(GPC) = 19,300 g/mol, PDI = 1.51) exhibited the intense fluorescence emission at ambient temperature. Moreover, the fluorescent intensity of PAHMA- b -PDMAEMA in CHCl3 was sensitive to the ultraviolet irradiation at 365 nm, which increased within the first 10 min and later decreased when irradiation time was prolonged to 30 min or longer. The well distributed, self-assembled micelles composed of azobenzene-containing amphiphilic diblock copolymers, (PAHMA- b -QPDMAEMA)s (QPDMAEMA is quaternized PDMAEMA), in the mixed N,N -dimethyl formamide (DMF)/H2O solutions were prepared. Their fluorescent intensities decreased with the increasing amount of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5652,5662, 2008 [source] Synthesis and self-assembly of helical polypeptide-random coil amphiphilic diblock copolymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2008Shiao-Wei Kuo Abstract Three amphiphilic rod-coil diblock copolymers, poly(2-ethyl-2-oxazoline- b -,-benzyl- L -glutamate) (PEOz- b -PBLG), incorporating the same-length PEOz block length and various lengths of their PBLG blocks, were synthesized through a combining of living cationic and N -carboxyanhydride (NCA) ring-opening polymerizations. In the bulk, these block copolymers display thermotropic liquid crystalline behavior. The self-assembled aggregates that formed from these diblock copolymers in aqueous solution exhibited morphologies that differed from those obtained in ,-helicogenic solvents, that is, solvents in which the PBLG blocks adopt rigid ,-helix conformations. In aqueous solution, the block copolymers self-assembled into spherical micelles and vesicular aggregates because of their amphiphilic structures. In helicogenic solvents (in this case, toluene and benzyl alcohol), the PEOz- b -PBLG copolymers exhibited rod-coil chain properties, which result in a diverse array of aggregate morphologies (spheres, vesicles, ribbons, and tube nanostructures) and thermoreversible gelation behavior. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3108,3119, 2008 [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] Multiple morphologies from a novel diblock copolymer containing dendronized polymethacrylate and linear poly(ethylene oxide)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2005Cai-Xia Cheng Abstract A novel amphiphilic diblock copolymer, consisting of dendronized polymethacrylate- b -poly(ethylene oxide), was synthesized via atom transfer radical polymerization; from it, micellelike aggregates of various morphologies, prepared under near-equilibrium conditions, were studied with transmission electron microscopy and scanning electron microscopy. The effects of various factors on the aggregate morphologies of the amphiphilic copolymer, such as the water content, the copolymer concentration, and the type of common solvent, were investigated systematically. The unique architecture of the block copolymer led to morphological variety and peculiarities such as dendritic and shuttle-shaped aggregates, which could be attributed to the effective packing of the bulky side chains, that is, another driving force for the aggregates. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2291,2297, 2005 [source] Nanostructured thermosets from self-assembled amphiphilic block copolymer/epoxy resin mixtures: effect of copolymer content on nanostructuresPOLYMER INTERNATIONAL, Issue 4 2010Miren Blanco Abstract Nanostructure formation in thermosets can allow the design of materials with interesting properties. The aim of this work was to obtain a nanostructured epoxy system by self-assembly of an amphiphilic diblock copolymer in an unreacted epoxy/amine mixture followed by curing of the matrix. The copolymer employed was polystyrene- block -poly(methyl methacrylate) (PS- b -PMMA). The thermoset system, formed by a diglycidyl ether of bisphenol A-type epoxy resin and diaminodiphenylmethane hardener, was chosen to ensure the miscibility of most of the PMMA block until matrix gelation. Transparent materials with microphase-separated domains were obtained for copolymer contents lower than 40 wt%. In systems containing 20 and 30 wt% block copolymer, the PS block formed spherical micelles or worm-like structures before curing, which were stabilized through curing by the more compatible PMMA block phase. Nanostructured thermoset systems were successfully synthesized for self-assembled amphiphilic block copolymer,epoxy/amine mixtures for copolymer contents lower than 40 wt%. Copyright © 2009 Society of Chemical Industry [source] Methoxypolyethylene glycol- block -polycaprolactone diblock copolymers reduce P-glycoprotein efflux in the absence of a membrane fluidization effect while stimulating P-glycoprotein ATPase activityJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2007Jason Zastre Abstract We have previously shown that amphiphilic diblock copolymers composed of methoxypolyethylene glycol- b -polycaprolactone (MePEG- b -PCL) increased the cellular accumulation and reduced the basolateral to apical flux of the P-glycoprotein substrate, rhodamine 123 (R-123) in caco-2 cells. The purpose of this study was to investigate membrane perturbation effects of MePEG- b -PCL diblock copolymers with erythrocyte membranes and caco-2 cells and the effect on P-gp ATPase activity. The diblock copolymer MePEG17 -b-PCL5 induced increasing erythrocyte hemolysis at concentrations which correlated with increasing accumulation of R-123 into caco-2 cells. However, no increase in cellular accumulation of R-123 by non-P-gp expressing cells was observed, suggesting that diblock did not enhance the transmembrane passive diffusion of R-123, but that the accumulation enhancement effect of the diblock in caco-2 cells was likely mediated primarily via P-gp inhibition. Fluorescence anisotropy measurements of membrane fluidity and P-gp ATPase activity demonstrated that MePEG17 - b -PCL5 decreased caco-2 membrane fluidity while stimulating ATPase activity approximately threefold at concentrations that maximally enhanced R-123 caco-2 accumulation. These results suggest that inhibition of P-gp efflux by MePEG17 - b -PCL5 does not appear to be related to increases in membrane fluidity or through inhibition in P-gp ATPase activities, which are two commonly reported cellular effects for P-gp inhibition mediated by surfactants. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 864,875, 2007 [source] Synthesis of azobenzene-containing polymers via RAFT polymerization and investigation on intense fluorescence from aggregates of azobenzene-containing amphiphilic diblock copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2008Jie Xu Abstract The well-defined azobenzene-containing homopolymers, poly{6-(4-phenylazophenoxy)hexyl methacrylate (AHMA)} (PAHMA), were synthesized via reversible addition fragmentation chain transfer polymerization (RAFT) in anisole solution using 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the RAFT agent and 2,2,-azobisisobutyronitrile (AIBN) as the initiator. The first-order kinetic plot of the polymerization and the linear dependence of molecular weights of the homopolymers with the relatively low polydispersity index values (PDIs , 1.25) on the monomer conversions were observed. Furthermore, the amphiphilic diblock copolymer, poly{6-(4-phenylazophenoxy)hexyl methacrylate (AHMA)}- b -poly{2-(dimethylamino)ethyl methacrylate (DMAEMA)} (PAHMA- b -PDMAEMA), was prepared with the obtained PAHMA as the macro-RAFT agent. The structures and properties of the polymers were characterized by 1H NMR and GPC, respectively. Interestingly, the amphiphilic diblock copolymers in chloroform (CHCl3) solution (PAHMA23 - b -PDMAEMA97 (4 × 10,5 M, Mn(GPC) = 18,400 g/mol, PDI = 1.48) and PAHMA28 - b -PDMAEMA117 (6 × 10,5 M, Mn(GPC) = 19,300 g/mol, PDI = 1.51) exhibited the intense fluorescence emission at ambient temperature. Moreover, the fluorescent intensity of PAHMA- b -PDMAEMA in CHCl3 was sensitive to the ultraviolet irradiation at 365 nm, which increased within the first 10 min and later decreased when irradiation time was prolonged to 30 min or longer. The well distributed, self-assembled micelles composed of azobenzene-containing amphiphilic diblock copolymers, (PAHMA- b -QPDMAEMA)s (QPDMAEMA is quaternized PDMAEMA), in the mixed N,N -dimethyl formamide (DMF)/H2O solutions were prepared. Their fluorescent intensities decreased with the increasing amount of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5652,5662, 2008 [source] Encapsulation of silver nanoparticles within micropores of block copolymers constructed by emulsion-induced methodJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2008Koji Ishizu An encapsulation of silver nanoparticles has been developed based on a template technique. Microporous films containing Ag+ ions were constructed by emulsion micelles of PEO- block- PMMA amphiphilic diblock copolymers. Ag+ ions are located around peripheral PEO phases of micropores. Subsequently, Ag nanoparticles (ca. 23 nm in diameter) within the micropore have been prepared by the addition of a chemical reductant, e.g. NaBH4. [source] Synthesis of new amphiphilic diblock copolymers containing poly(ethylene oxide) and poly(,-olefin)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Yingying Lu Abstract This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s-PS), and elastomers, such as poly(ethylene- co -1-octene) and poly(ethylene- co -styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ,270 °C to low glass-transition temperature ,,60 °C. The chemistry involves two reaction steps, including the preparation of a borane group-terminated polyolefin by the combination of a metallocene catalyst and a borane chain-transfer agent as well as the interconversion of a borane terminal group to an anionic (O,K+) terminal group for the subsequent ring-opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of ,-olefins to the ring-opening polymerization of ethylene oxide. The well-defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (Mw/Mn < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416,3425, 2002 [source] Efficient Encapsulation of Plasmid DNA in pH-Sensitive PMPC,PDPA Polymersomes: Study of the Effect of PDPA Block Length on Copolymer,DNA Binding AffinityMACROMOLECULAR BIOSCIENCE, Issue 5 2010Hannah Lomas Abstract We report the self-assembly of a series of amphiphilic diblock copolymers comprising a biocompatible, hydrophilic block, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and a pH-sensitive block, poly(2-(diisopropylamino)ethyl methacrylate) (PDPA), into a dispersion of colloidally stable, nanometer-sized polymersomes at physiological pH and salt concentration. The pH-sensitivity of the PDPA block affords the electrostatic interaction of these block copolymers with nucleic acids at endocytic pH, as a result of the protonation of its tertiary amine groups at pH values below its pKa. Herein we investigate the effect of PDPA block length on the binding affinity of the block copolymer to plasmid DNA. 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