Block Copolymers (block + copolymer)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Block Copolymers

  • ab block copolymer
  • amphiphilic block copolymer
  • double hydrophilic block copolymer
  • hybrid block copolymer
  • hydrophilic block copolymer
  • rod-coil block copolymer
  • star block copolymer

  • Terms modified by Block Copolymers

  • block copolymer nanoparticle
  • block copolymer poly
  • block copolymer thin film

  • Selected Abstracts

    Integration of Density Multiplication in the Formation of Device-Oriented Structures by Directed Assembly of Block Copolymer,Homopolymer Blends

    Guoliang Liu
    Abstract Non-regular, device-oriented structures can be directed to assemble on chemically nanopatterned surfaces such that the density of features in the assembled pattern is multiplied by a factor of two or more compared to the chemical pattern. By blending the block copolymers with homopolymers and designing the chemical pattern rationally, complicated structures such as bends, jogs, junctions, terminations, and combined structures are fabricated. Previously, directed assembly of block copolymers has been shown to enhance the resolution of lithographic processes for hexagonal arrays of spots and parallel lines, corresponding to the bulk morphologies of block copolymer systems, but this is the first demonstration of enhanced resolution for more complicated, device-oriented features. This fundamental knowledge broadens the range of technologies that can be served by the directed assembly of block copolymers. [source]

    Directed Helical Growth: A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization (Adv. Funct.

    Crystalline helices (PLLA crystallization directed by helical confined microdomains) and crystalline cylinders (phase transformation of helical nano structures dictated by crystallization) are obtained by controlling the crystallization temperature of PLLA with respect to the glass transition temperature of PS in PS-PLLA block copolymers; this process is described by J.-W. Chiang et al. on page 448. A spring-like behavior of the PLLA helical nanostructures embedded in the PS matrix can be driven by crystallization, so as to dictate the transformation of the helices, resulting in crystalline cylinders that might represent a possible avenue for the design of switchable large-strain actuators. [source]

    A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization

    Yeo-Wan Chiang
    Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source]

    Sustained and Extended Release with Structural and Activity Recovery of Lysozyme from Complexes with Sodium (Sulfamate Carboxylate) Isoprene/Ethylene Oxide Block Copolymer

    Gao Gao
    Abstract The complexation of lysozyme and sodium (sulfamate carboxylate) isoprene/ethylene oxide (SCIEO) at pH,=,7.4 and the release of lysozyme from the complexes in the presence of NaCl were investigated. Through electrostatic and hydrophobic interactions, lysozyme and SCIEO form stable complex nanoparticles. The complexation partially disturbs the structure of lysozyme. Some of the hydrophobic residues of lysozyme are exposed to bind with SCIEO. The complexation leads to loss of most of the lysozyme activity. In the presence of NaCl, lysozyme can be released from the complexes. The released lysozyme molecules recover their native structure and activity completely. In the condition of physiological pH and ionic strength, a sustained and extended release of lysozyme was achieved. [source]

    Microphase-Separated Poly(vinylpyridine) Block Copolymer Prepared with a Novel Bifunctional Initiator

    Masami Shoji
    Abstract A vinylpyridine block copolymer was prepared by stepwise controlled/living radical polymerization with a novel bifunctional initiator, 4-(2-bromopropanoyloxy)- N -(p -methylbenzyloxy)-2,2,6,6-tetramethylpiperidine. The initiator was synthesized in a facile manner using commercially available p -xylene and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy TEMPO). Through stepwise atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and nitroxide-mediated radical polymerization (NMRP) of 4-vinylpyridine (4VP), the PMMA- b- P4VP copolymer was prepared with a wide range of the copolymer compositions. Microphase-separation was demonstrated in cross sectional TEM images of self-standing block copolymer membranes. [source]

    Synthesis, Sequential Crystallization and Morphological Evolution of Well-Defined Star-Shaped Poly(, -caprolactone)- b -poly(L -lactide) Block Copolymer,

    Jing-Liang Wang
    Abstract Summary: Well-defined star-shaped poly(, -caprolactone)- b -poly(L -lactide) copolymers (PCL- b -PLLA) were synthesized via sequential block copolymerization, and their molecular weights and arm length ratio could be accurately controlled. Both differential scanning calorimetry and wide angle X-ray diffraction analysis indicated that the crystallization of both the PLLA and PCL blocks within the star-shaped PCL- b -PLLA copolymer could be adjusted from the arm length of each block, and both blocks mutually influenced each other. The sequential isothermal crystallization process of both the PLLA and PCL blocks within the PCL- b -PLLA copolymers was directly observed with a polarized optical microscope, and the isothermal crystallization of the PCL segments was mainly templated by the existing spherulites of PLLA. Moreover, the PLLA blocks within the star-shaped PCL- b -PLLA copolymer progressively changed from ordinary spherulites to banded spherulites when the arm length ratio of PCL to PLLA was increased while concentric spherulites were observed for the linear analog. Significantly, these novel spherulites with concentric or banded textures and the morphological evolution of the spherulites have been observed for the first time in the PCL- b -PLLA block copolymers. [source]

    Immiscible Poly(L -lactide)/Poly(, -caprolactone) Blends: Influence of the Addition of a Poly(L -lactide)-Poly(oxyethylene) Block Copolymer on Thermal Behavior and Morphology

    Giovanni Maglio
    Abstract Summary: A binary blend of poly (L -lactide) (PLLA) and poly(, -caprolactone) (PCL) of composition 70:30 by weight was prepared using a twin screw miniextruder and investigated by differential scanning calorimetry (DSC), optical microscopy and scanning electron microscopy (SEM). Ternary 70:30:2 blends were also obtained by adding either a diblock copolymer of PLLA and poly(oxyethylene) (PEO) or a triblock PLLA-PCL-PLLA copolymer as a third component. Optical microscopy revealed that the domain size of dispersed PCL domains is reduced by one order of magnitude in the presence of both copolymers. SEM confirmed the strong reduction in particle size upon the addition of the copolymers, with an indication of an enhanced emulsifying effect in the case of the PLLA-PEO copolymer. These results are analyzed on the basis of solubility parameters of the blend components. Optical micrograph of M3EG2 blend melt quenched at 125,C. [source]

    Sphere-to-Rod Transition of Micelles formed by the Semicrystalline Polybutadiene- block -Poly(ethylene oxide) Block Copolymer in a Selective Solvent

    Adriana M. Mihut
    Abstract We present a morphological study of the micellization of an asymmetric semicrystalline block copolymer, poly(butadiene)- block -poly(ethylene oxide), in the selective solvent n -heptane. The molecular weights of the poly(butadiene) (PB) and poly(ethylene oxide) (PEO) blocks are 26 and 3.5,kg,,mol,1, respectively. In this solvent, micellization into a liquid PEO-core and a corona of PB-chains takes place at room temperature. Through a thermally controlled crystallization of the PEO core at ,30,C, spherical micelles with a crystalline PEO core and a PB corona are obtained. However, crystallization at much lower temperatures (,196,C; liquid nitrogen) leads to the transition from spherical to rod-like micelles. With time these rod-like micelles aggregate and form long needles. Concomitantly, the degree of crystallinity of the PEO-cores of the rod-like micelles increases. The transition from a spherical to a rod-like morphology can be explained by a decrease of solvent power of the solvent n -heptane for the PB-corona chains: n -Heptane becomes a poor solvent at very low temperatures leading to a shrinking of the coronar chains. This favors the transition from spheres to a morphology with a smaller mean curvature, that is, to a cylindrical morphology. [source]

    A Block Copolymer for Functionalisation of Polymersome Surfaces

    Stijn F. M. van Dongen
    Abstract A block copolymer was designed to functionalise the surface of polystyrene-based polymersomes via coaggregation. An ,,, -diacetylene-functionalised poly(ethylene glycol) (PEG) was coupled to an azide-terminated polystyrene via a Cu(I)-catalysed cycloaddition to produce a PS- b -PEG polymer with an acetylene at its hydrophilic extremity. Incorporation of this ,anchor' compound in the bilayer of a polymersome places its bio-orthogonal group at the surface of this aggregate. Its accessibility was demonstrated using an azido-functionalised Candida antarctica Lipase B (CalB), which retained its activity while immobilised on the polymersome. [source]

    Synthesis and Characterization of Novel Mesogen-Jacketed Liquid Crystalline Miktoarm Star Rod-Coil Block Copolymer

    Jianfang Chen
    Abstract 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. Miktoarm star rod-coil block copolymer. [source]

    Functional Polymeric Micelles Formed from a Novel Cationic Star Block Copolymer

    CHEMPHYSCHEM, Issue 10 2003
    Ren-Hua Jin Dr.
    Flowers made from stars: A star polymer, which consists of a porphyrin center to which four arms with cationic poly(ethyleneimine) (PEI) and hydrophobic poly(phenyloxazoline) (PPOZ) segments were attached, was synthesized and shown to form micelles in both aqueous and organic media (see picture). In aqueous media, the star formed a micelle in which a hydrophobic PPOZ core was surrounded by cationic corona PEI. The porphyrin moieties enclosed in the micellar core can effectively communicate with an ionic substrate enriched in the cationic corona. In organic media, the star gave a flowerlike micelle in which the ionomer segment PEI assembled to form a core and the nonionic PPOZ segments formed a looplike corona coating the core. [source]

    Synthesis, Morphology, and Properties of Poly(3-hexylthiophene)- block -Poly(vinylphenyl oxadiazole) Donor,Acceptor Rod,Coil Block Copolymers and Their Memory Device Applications

    Yi-Kai Fang
    Abstract Novel donor,acceptor rod,coil diblock copolymers of regioregular poly(3-hexylthiophene) (P3HT)- block -poly(2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiaz-ole) (POXD) are successfully synthesized by the combination of a modified Grignard metathesis reaction (GRIM) and atom transfer radical polymerization (ATRP). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low-lying highest occupied molecular orbital (HOMO) energy level (,6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT- b -POXD exhibits a non-volatile bistable memory or insulator behavior depending on the P3HT/POXD block ratio and the resulting morphology. The ITO/P3HT44 - b - POXD18/Al memory device shows a non-volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor-acceptor rod-coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications. [source]

    Dual-Tone Patterned Mesoporous Silicate Films Templated From Chemically Amplified Block Copolymers

    Sivakumar Nagarajan
    Abstract Directly patterned mesoporous silicate films are prepared using positive- and negative-tone strategies by performing phase selective silica condensation within lithographically exposed poly(styrene- b - tert -butyl acrylate) (PS- b -PtbA) templates containing photoacid generators. The use of supercritical fluid as a process medium enables rapid diffusion of the silicate precursor within the prepatterned block copolymer template film without disrupting its morphology. Template exposure through the mask triggers area selective generation of acid, which in turn both deprotects the poly(tert -butyl acrylate) block to yield a poly(acrylic acid) block and provides a catalyst for silica precursor condensation yielding pattern formation at the device level. Because the acid generated in the UV exposed field preferentially segregates into hydrophilic poly(acrylic acid) domains of the phase segregated, deprotected block copolymer, precursor condensation is simultaneously controlled at nanoscopic length scales via templating by the underlying block copolymer morphology. The ability of PS- b -PtbA to undergo chemical transformation in two stages, deprotection followed by crosslinking, enables precise replications of the photomask in positive and negative tones. Detemplating via calcination yields patterned mesoporous silicate films without etching. Template formulations are optimized using infrared spectroscopic studies and the silicate films are characterized using electron microscopy and scanning force microscopy. [source]

    A General Strategy to Disperse and Functionalize Carbon Nanotubes Using Conjugated Block Copolymers

    Jianhua Zou
    Abstract A general strategy to disperse and functionalize pristine carbon nanotubes in a single-step process is developed using conjugated block copolymers. The conjugated block copolymer contains two blocks: a conjugated polymer block of poly(3-hexylthiophene), and a functional non-conjugated block with tunable composition. When the pristine carbon nanotubes are sonicated with the conjugated block copolymers, the poly(3-hexylthiophene) blocks bind to the surface of de-bundled carbon nanotubes through non-covalent ,,, interactions, stabilizing the carbon nanotube dispersion, while the functional blocks locate at the outer surface of carbon nanotubes, rendering the carbon nanotubes with desired functionality. In this paper, conjugated block copolymers of poly(3-hexylthiophene)- b -poly(methyl methacrylate), poly(3-hexylthiophene)- b -poly(acrylic acid), and poly(3-hexylthiophene)- b -poly(poly(ethylene glycol) acrylate) are used to demonstrate this general strategy. [source]

    Thermosensitive Nanostructures Comprising Gold Nanoparticles Grafted with Block Copolymers,

    D. Li
    Abstract Binary thermosensitive nanocomposites are fabricated by grafting block copolymers of poly(N -isopropylacrylamide) and poly(methoxy-oligo(ethylene glycol) methacrylate) onto gold nanoparticles through consecutive, surface-initiated, atom-transfer radical polymerization (ATRP). These Au@copolymer nanocomposites display a well-defined core/shell nanostructure and have two thermosensitive points near 33 and 55,C in an aqueous suspension corresponding to the thermally induced conformational transition of inner homopolymer segments and outer oligo(ethylene glycol)-containing copolymer layer, respectively. Silver nanoparticles trapped within Au@copolymer nanocomposites with weakly crosslinked shells display thermally modulated catalytic activity as heterogeneous catalysts because of the thermosensitive collapse of the polymer layers. [source]

    Graphoepitaxial Assembly of Symmetric Block Copolymers on Weakly Preferential Substrates

    ADVANCED MATERIALS, Issue 38 2010
    Eungnak Han
    Weakly preferential substrates were utilized in a single step process to direct the assembly of symmetric PS- b -PMMA. The thickness dependence of domain orientation on weakly preferential substrates was exploited to dictate the lateral ordering of perpendicular lamellae. [source]

    Directed Self-Assembly of Block Copolymers on Two-Dimensional Chemical Patterns Fabricated by Electro-Oxidation Nanolithography

    ADVANCED MATERIALS, Issue 20 2010
    Ji Xu
    A hexagonal web of carboxylic-terminated nanostripes (left image, bright areas) is patterned onto a methyl-terminated surface of an octadecyltrichlorosilane monolayer. A thermally annealed polystyrene- block -poly(ethylene oxide) (PS- b -PEO) thin-film, spin-cast on the chemical pattern (right image), exhibits surface normal oriented cylindrical PEO microdomains on the methyl-terminated regions only. These chemical patterns effectively template the order and spatial orientation of diblock-copolymer microdomains. [source]

    A New Supramolecular Route for Using Rod-Coil Block Copolymers in Photovoltaic Applications

    ADVANCED MATERIALS, Issue 6 2010
    Nicolas Sary
    A new polymer blend formed by poly(3-hexylthiophene)-poly(4-vinylpyridine) (P3HT- P4VP) block copolymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is reported. The P4VP and PCBM are mixed together by weak supramolecular interactions, and the resulting materials exhibit microphase separated morphologies of electron-donor and electron-acceptor rich domains. The properties of the blend, used in photovoltaic devices as active layers, are also discussed. [source]

    One-Step Direct-Patterning Template Utilizing Self-Assembly of POSS-Containing Block Copolymers

    ADVANCED MATERIALS, Issue 43 2009
    Tomoyasu Hirai
    We report the self-assembly of organic-inorganic block copolymers (BCP) in thin-films by simple solvent annealing on unmodified substrates. The resulting vertically oriented lamellae and cylinders are converted to a hard silica mask by a single step highly selective oxygen plasma etching. The size of the resulting nanostructures in the case of cylinders is less than 10,nm. [source]

    A Polymersome Nanoreactor with Controllable Permeability Induced by Stimuli-Responsive Block Copolymers

    ADVANCED MATERIALS, Issue 27 2009
    Kyoung Taek Kim
    A method to generate and control the permeability of polymersome membranes using mixtures of amphiphilic and stimuli-responsive boronic acid-containing block copolymers is reported. The latter block copolymers form phase-separated domains in the polymersomes, which can be dissolved by increasing the pH of the medium or by introducing sugar molecules that covalently bind to the boronic acid moieties. [source]

    A New Level of Hierarchical Structure Control by Use of Supramolecular Self-Assembled Dendronized Block Copolymers,

    ADVANCED MATERIALS, Issue 23 2008
    Chaoxu Li
    Complexation of dendronized block copolymers with sulfate alkyl tails forms unprecedented hierarchically ordered bulk structures, including rectangular-in-lamellar, tetragonal-in-lamellar, hexagonal-in-lamellar and lamellar-in-lamellar. These novel liquid-crystalline morphologies, which can be designed at low length scales in these systems, are expected to provide final materials with not only unprecedented structural complexity, but also tunable physical properties. [source]

    New Biodegradable Amphiphilic Block Copolymers of , -Caprolactone and , -Valerolactone Catalyzed by Novel Aluminum Metal Complexes

    Jing Yang
    Abstract Summary: In our previous study [J. Yang, L. Jia, L. Yin, J. Yu, Z. Shi, Q. Fang, A. Cao, Macromol. Biosci.2004, 4, 1092.], new biodegradable copolymers of diblock methoxy poly(ethylene glycol)- block -poly(, -caprolactone) and methoxy poly(ethylene glycol)- block -poly(, -valerolactone), and triblock poly(, -caprolactone)- block -poly(ethylene glycol)- block -poly(, -caprolactone) and poly(, -valerolactone)- block -poly(ethylene glycol)- block -poly(, -valero-lactone) bearing narrow molecular weight distributions and well-defined block architectures were reported to be prepared with our original aluminum metal complex templates. This work will continue to report new investigations on their water solubility, and reversible thermal responsive micellization and solution to gel transition in distilled water. Among the new synthesized copolymers (P1,P23), seven diblock or triblock samples (P3, P6, P7, P11, P12, P19, and P21) with higher hydrophilic building block populations were revealed to be water soluble under ambient temperature. By means of UV spectrophotometer attached with a thermostat, important parameters as critical micellization mass concentrations (CMCs) and critical micellization temperatures (CMTs) were characterized for these new amphiphile dilute aqueous solution with the aid of an lipophilic organic dye probe of 1,6-diphenyl-1,3,5-hexatriene (DPH). Furthermore, the critical gelation temperatures (CGTs) were simultaneously investigated for these water-soluble block copolymers via a tube tilting method. It was found that the CMC, CMT, and CGT were strongly affected by the population and nature of the hydrophobic building blocks, and a higher hydrophobicity of the new amphiphilic block copolymer finally led to lower CMC and CMT, and higher CGT. In addition, the salts of KBr and NaCl were found to play as a salt-out effect on the solution to gel transition for the diblock P6 and triblock P11, exhibiting an interesting tunable gelation temperature close to 35,42,C. These results will pave new possibility for the synthesized block structural amphiphiles as potential biomaterials to be applied in vivo. Thermal responsive micellization and gelation of diblock MPEG- b -PCL/PVL and triblock PVL/PCL- b -PEG- b -PCL/PVL. [source]

    Characterization of New Amphiphilic Block Copolymers of N -Vinyl Pyrrolidone and Vinyl Acetate, 1 , Analysis of Copolymer Composition, End Groups, Molar Masses and Molar Mass Distributions,

    Nick Fandrich
    Abstract New amphiphilic block copolymers consisting of N -vinyl pyrrolidone and vinyl acetate were synthesized via controlled radical polymerization using a reversible addition/fragmentation chain transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) system. The synthesis was carried out in 1,4-dioxane as process solvent. In order to get conclusions on the mechanism of the polymerization the molecular structure of formed copolymers was analysed by means of different analytical techniques. 13C NMR spectroscopy was used for the determination of the monomer ratios. End groups were analysed by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This technique was also used to determine possible fragmentations of the RAFT end groups. By means of a combination of size exclusion chromatography, 13C NMR and static light scattering molar mass distributions and absolute molar masses could be analysed. The results clearly show a non-ideal RAFT mechanism. [source]

    The Structure of Water in PEO-Based Segmented Block Copolymers and its Effect on Transition Temperatures

    Debby Husken
    Abstract The effect of water on block copolymers that contain hydrophilic PEO flexible segments is studied. The polyether phase consisted of either PEO or mixtures of PEO and hydrophobic PTMO, monodisperse crystallisable T6T6T was used as hard segments. Water absorption as a function of relative humidity and PEO content were studied. The PEO melting temperature and crystallinity were strongly reduced when the copolymer absorbed water, while the PTMO phase remained unaffected by its presence. Freezing water was present in the PEO-based copolymers when the PEO phase contained ,30 vol.-% water, its relative amount being almost independent of PEO concentration and molecular weight and the presence of hydrophobic PTMO segments. [source]

    Segmented Block Copolymers with Monodisperse Aramide End-Segments

    Araichimani Arun
    Abstract Segmented block copolymers were synthesized using monodisperse diaramide (T,T) as hard segments and PTMO with a molecular weight of 2,900 g,,mol,1 as soft segments. The aramide: PTMO segment ratio was increased from 1:1 to 2:1 thereby changing the structure from a high molecular weight multi-block copolymer to a low molecular weight end-block copolymer. The thermal and thermal-mechanical properties were studied by DSC and DMA. Also studied were the tensile and the elastic properties as well as the melt rheological behavior as a function of frequency. The crystallinity of aramide in the end-block copolymers was found to be higher than in the multi-block copolymer. [source]

    Segmented Block Copolymers with Terephthalic-Extended Poly(ethylene oxide) Segments

    Debby Husken
    Abstract Segmented block copolymers comprised of flexible PEO segments and monodisperse crystallizable bisestertetraamide segments have been synthesized. The influence of the terephthalic units in the soft phase on the transitions and the thermal mechanical and elastic properties are studied. The presence of terephthalic units in the copolymer increases the glass transition temperature of the soft phase by ,5,C. The low-temperature flexibility of the copolymers is improved because of the lower crystallinity and melting temperature of PEO. With the use of terephthalic-extended PEO segments, segmented block copolymers with low moduli (G',<,15 MPa) and good elastic properties could be obtained. [source]

    Novel Amphiphilic Styrene-Based Block Copolymers for Induced Surface Reconstruction

    Lutz Funk
    Abstract This paper describes the synthesis of amphiphilic block copolymers by living radical polymerization (NMP) of new styrene-like monomers. The polar monomers (ethylene oxide side chains and free hydroxyl- or amino-groups after deprotection) were polymerized in a "protected form" to adjust the solubility of the monomers. In this way high molar mass polymers with a narrow polydispersity (around or below 1.2) were accessible. In the bulk state hydrophobic and hydrophilic domains demix. By exposing thin films of these polymers to vacuum (air) or alternatively to water or a hydrophilic surface it becomes possible to switch the surface polarity reversibly between contact angles of about 105 and 83 as a result of surface reconstruction. Through side chains of different length and with different functionalities, it was possible to adjust the glass transition temperatures to values between ,2,C to 140,C for the hydrophilic blocks and ,30,C to 100,C for the hydrophobic block. The wide range of the glass temperatures allowed it to find a block copolymer system with a slow kinetic concerning the surface reconstruction process, so that a mechanistic examination of the process by AFM was possible. It got, thereby, possible to detect the break-up of the hydrophobic surface lamella and the upfold of the hydrophilic lamella in contact with water. [source]

    Synthesis and Characterization of Styrene/Butyl Acrylate Linear and Star Block Copolymers via Atom Transfer Radical Polymerization

    Jinyu Huang
    Abstract Summary: Well-defined styrene (S) and butyl acrylate (BA) linear and star-like block copolymers are synthesized via atom transfer radical polymerization (ATRP) using di- and trifunctional alkyl halide initiators employing the Cu/PMDETA (N,N,N,,N,,N,-pentamethyldiethylenetriamine) catalyst system. Initial addition of CuII deactivator and utilization of halogen exchange techniques suppresses the coupling of radicals and improves cross-propagation to a large extent, which results in better control over the polymerization. Two types of star-like PBA/PS block copolymers are prepared by using core-first techniques: a trifunctional PBA or PS macroinitiator extended with the other monomer. Block copolymers with a well-defined structure and low polydispersity (PDI,=,) are obtained in both cases. A trifunctional PBA3 macroinitiator with ,=,136,000 g,,mol,1 and PDI,=,1.15 is extended to (PBA-PS)3 star-like block copolymer with ,=,171,100 g,,mol,1 and PDI,=,1.15. A trifunctional PS3 macroinitiator with ,=,27,000 g,,mol,1 and PDI,=,1.16 g,,mol,1 is extended to (PS-PBA)3 with ,=,91,500 g,,mol,1 and PDI,=,1.40. The individual star-like macromolecules as well as their aggregates are visualized by atomic force microscopy (AFM) where the PS and PBA adopt the globular and extended conformation, respectively. For the PBA core star block copolymers, PS segments tend to aggregate either intramolecularly or intermolecularly. PS core star block copolymers form aggregates with a PS core and emanating PBA chains. Most aggregates have ,n,,3' arms but minor amounts of ,defective' stars with 4, 5, 8, or 11 arms are also observed. The AFM analysis shows that PS core star block copolymers contain about 92% three-arm block copolymers, and the efficiency of cross-propagation is 97.3%. Schematic representation of the synthesis of BA/S star-like block copolymers by ATRP, and their resultant AFM images. [source]

    Application of Nitroxide-Terminated Polymers Prepared by Sonochemical Degradation in the Synthesis of Block Copolymers

    Martina Bartsch
    Abstract Summary: The ultrasonic irradiation of a polymer solution results in the breakage of macromolecular CC bonds. In the presence of radical scavengers the formed macroradicals are prevented from termination reactions as combination or disproportionation. Using nitroxides as trapping agents the polymer is transformed into a macroinitiator, which can be used in controlled free-radical polymerization to synthesize block copolymers. In this work several polymers were exposed to sonochemical degradation and terminated with various nitroxides, e.g. OH-TEMPO and TIPNO. In a second reaction step the prepared polymer-nitroxide-adducts were applied as macroinitiators in controlled free-radical polymerizations with styrene. The obtained products were mixtures of block copolymer and the corresponding homopolymers. The visco-elastic properties were investigated by rheological analysis. A special separation technique with selective solvents was applied to determine the content of block copolymer. Synthesis of block copolymers with sonochemically prepared macroinitiators. [source]

    Synthesis and Characterization of Block Copolymers of , -Caprolactone and DL -Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol)

    Ming-Hsi Huang
    Abstract Biodegradable copolymers were prepared by ring-opening polymerization of sequentially added , -caprolactone and DL -lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by 1H NMR, SEC, IR, DSC, TGA, and X-ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA-containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering. Block copolymerization of , -caprolactone and DL -lactide initiated by dihydroxyl PEG. [source]