Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Copolymers

  • ab block copolymer
  • ab diblock copolymer
  • aba triblock copolymer
  • abc triblock copolymer
  • acetate copolymer
  • acid copolymer
  • acrylate copolymer
  • alcohol copolymer
  • alternating copolymer
  • amphiphilic abc triblock copolymer
  • amphiphilic block copolymer
  • amphiphilic copolymer
  • amphiphilic diblock copolymer
  • amphiphilic graft copolymer
  • anhydride copolymer
  • biodegradable copolymer
  • block copolymer
  • branched copolymer
  • butadiene copolymer
  • comb copolymer
  • comb-shaped copolymer
  • conducting copolymer
  • conjugated copolymer
  • crystalline copolymer
  • cyclic olefin copolymer
  • diblock copolymer
  • double hydrophilic block copolymer
  • ethylene copolymer
  • ethylene vinyl acetate copolymer
  • ethylene-acrylic acid copolymer
  • ethylene-vinyl acetate copolymer
  • fluorene copolymer
  • fluorinated copolymer
  • graft copolymer
  • grafted copolymer
  • hybrid block copolymer
  • hydrophilic block copolymer
  • hyperbranched copolymer
  • linear copolymer
  • liquid crystalline copolymer
  • maleic anhydride copolymer
  • methacrylate copolymer
  • miktoarm star copolymer
  • multiblock copolymer
  • new copolymer
  • novel copolymer
  • obtained copolymer
  • olefin copolymer
  • polyethylene copolymer
  • polyfluorene copolymer
  • polyurethane copolymer
  • propylene copolymer
  • random copolymer
  • resulting copolymer
  • rod-coil block copolymer
  • star block copolymer
  • star copolymer
  • star-block copolymer
  • statistical copolymer
  • styrene copolymer
  • styrene-butadiene copolymer
  • synthesized copolymer
  • tetrablock copolymer
  • tri-block copolymer
  • triblock copolymer
  • vinyl acetate copolymer
  • vinyl alcohol copolymer

  • Terms modified by Copolymers

  • copolymer blend
  • copolymer blend film
  • copolymer chain
  • copolymer composition
  • copolymer composition distribution
  • copolymer concentration
  • copolymer consisting
  • copolymer containing
  • copolymer content
  • copolymer film
  • copolymer gel
  • copolymer hydrogel
  • copolymer melt
  • copolymer membrane
  • copolymer micelle
  • copolymer microsphere
  • copolymer mixture
  • copolymer nanoparticle
  • copolymer network
  • copolymer poly
  • copolymer solution
  • copolymer structure
  • copolymer system
  • copolymer thin film
  • copolymer used

  • 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]

    B,Z DNA Transition Triggered by a Cationic Comb-Type Copolymer

    Naohiko Shimada
    Abstract The conformational transition from right-handed B,DNA to left-handed Z,DNA,the B,Z transition,has received increased attention recently because of its potential roles in biological systems and its applicability to bionanotechnology. Though the B,Z transition of poly(dG,dC),,poly(dG,dC) is inducible under high salt concentration conditions (over 4,M NaCl) or by addition of multivalent cations, such as hexaamminecobalt(III), no cationic polymer were known to induce the transition. In this study, it is shown by circular dichroism and UV spectroscopy that the cationic comb-type copolymer, poly(L -lysine)- graft -dextran, but not poly(L -lysine) homopolymer or a basic peptide, induces the B,Z transition of poly(dG,dC),,poly(dG,dC). At a cationic amino group concentration of 10,4,M the copolymer stabilizes Z,DNA. The transition pathway from the B to the Z form is different to that observed previously. We speculate that the cationic backbone of the copolymer, which reduces electrostatic repulsion among DNA phosphate groups, and the hydrophilic dextran chains, which reduce activity of water, cooperate to induce the B,Z transition. The copolymer specifically modified the micro-environment around DNA molecules to induce Z,DNA formation through stable and spontaneous inter-polyelectrolyte complex formation. [source]

    pH-Responsive Flower-Type Micelles Formed by a Biotinylated Poly(2-vinylpyridine)- block -poly(ethylene oxide)- block -poly(, -caprolactone) Triblock Copolymer

    Kathy Van Butsele
    Abstract In the present work, a method is proposed to assemble pH-responsive, flower-like micelles that can expose a targeting unit at their periphery upon a decrease in pH. The micelles are composed of a novel biotinylated triblock copolymer of poly(,, -caprolactone)- block -poly(ethylene oxide)- block -poly(2-vinylpyridine) (PCL- b -PEO- b -P2VP) and the non-biotinylated analogue. The block copolymers are synthesized by sequential anionic and ring-opening polymerization. The pH-dependent micellization behaviour in aqueous solution of the triblock copolymers developed is studied using dynamic light scattering, zeta potential, transmission electron microscopy (TEM), and fluorimetric measurements. The shielding of the biotin at neutral pH and their availability at the micelle surface upon protonation is established by TEM and surface plasmon resonance with avidin and streptavidin-coated gold surfaces. The preliminary stealthy behavior of these pH-responsive micelles is examined using the complement activation (CH50) test. [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]

    Hole Injection in a Model Fluorene,Triarylamine Copolymer

    Hon Hang Fong
    Abstract Recent developments in synthesis and purification have yielded conjugated polymers with hole mobilities exceeding 0.01,cm2 V,1 s,1. Essential to harvesting the potential of these materials in organic light emitting diodes (OLEDs) is the identification of suitable ohmic contacts. Using a model fluorene copolymer that shows high-mobility, non-dispersive hole transport, it is demonstrated that electrodes commonly used as anodes in OLEDs are very poor hole injectors. Injection from Au and indium tin oxide anodes is limited by energy barriers of 0.75 and 0.65,eV, respectively, and the injected current is found to be temperature independent,a prediction that was not reproduced by the leading injection model for disordered organic semiconductors. Injection from a poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) anode, on the other hand, is found to become less efficient with electric field, a behavior which is currently not understood. In thinner poly[(9,9,-dioctylfluorenyl-2,7-diyl)- co -(4,4,-(N -(4- sec -butyl))diphenylamine)] films, which are of relevance to OLEDs, ohmic losses on the PEDOT:PSS layer are found to limit the flow of current. These results illustrate the opportunity to further improve the performance of OLEDs as well as the challenge posed by high mobility conjugated polymers for the design of hole injection layers. [source]

    A New Donor,Acceptor,Donor Polyfluorene Copolymer with Balanced Electron and Hole Mobility,

    A. Gadisa
    Abstract A new alternating polyfluorene copolymer poly[2,7-(9,9-dioctylfluoren)- alt -5,5-(5,,8,-di-2-thienyl-(2,,3,-bis-(3,,-octyloxyphenyl)-quinoxaline))] (APFO-15), which has electron donor,acceptor,donor units in between the fluorene units, is synthesized and characterized. This polymer has a strong absorption and emission in the visible range of the solar spectrum. Its electroluminescence and photoluminescence emissions extend from about 560 to 900 nm. Moreover, solar cells with efficiencies in excess of 3.5,% have been realized from blends of APFO-15 and an electron acceptor molecule, a methanofullerene [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM). It has also been observed that electron and hole transport is balanced both in the pure polymer phase and in polymer/PCBM bulk heterojunction films, which makes this material quite attractive for applications in opto-electronic devices. [source]

    Perpendicularly Aligned, Size-and Spacing-Controlled Nanocylinders by Molecular-Weight Adjustment of a Homopolymer Blended in an Asymmetric Triblock Copolymer

    U. Ahn
    Abstract Perpendicularly arrayed and size-controlled nanocylinders have been prepared by simply blending an asymmetric polystyrene- block -polyisoprene- block -polystyrene triblock copolymer with polystyrene (the minority component) homopolymers of different molecular weights. The preference for perpendicular orientation or hexagonal ordering of the nanocylinders over a large area in the asymmetric block copolymer can be controlled by adjusting the molecular weight of the blended homopolymer, and the perfection of hexagonal ordering of the perpendicular cylinders can be tuned by using a substrate whose surface tension is much different from that of the majority component of the block copolymer. Such highly controlled nanostructured block-copolymer materials, which have been obtained by a simple method independent of film thickness and interfacial tension between the blocks and the substrates, have wide-ranging commercial potential, e.g., for use in membranes and nanotemplates with size-tunable pores, bandgap-controlled photonic crystals, and other nanotechnological fields demanding a specific nanosize and nanomorphology. [source]

    Polymer Solar Cells Based on a Low-Bandgap Fluorene Copolymer and a Fullerene Derivative with Photocurrent Extended to 850,nm,

    F. Zhang
    Abstract Polymer solar cells have been fabricated from a recently synthesized low band-gap alternating polyfluorene copolymer, APFO-Green2, combined with [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) from organic solutions. External quantum efficiencies (EQEs) of the solar cells show an onset at 850,nm and a peak of >,10,% located at 650,nm, which corresponds to the extended absorption spectrum of the polymer. Photocurrent of 3.0,mA,cm,2, photovoltage of 0.78,V, and power conversion efficiency of 0.9,% have been achieved in solar cells based on this new low-bandgap polymer under the illumination of air mass,1.5 (AM,1.5) (1000,W,m,2) from a solar simulator. [source]

    High-Gain Broadband Solid-State Optical Amplifier using a Semiconducting Copolymer,

    ADVANCED MATERIALS, Issue 1 2009
    Dimali Amarasinghe
    A dilute fluorene copolymer produces enhanced optical amplification. High gain with 1000 times optical amplification and a long lifetime is achieve in only 1mm of the material, and exciton,exciton annihilation is suppressed. [source]

    High-Efficiency White-Light Emission from a Single Copolymer: Fluorescent Blue, Green, and Red Chromophores on a Conjugated Polymer Backbone,

    ADVANCED MATERIALS, Issue 8 2007
    J. Luo
    The synthesis and properties of a single copolymer incorporating well-separated blue, green, and red chromophores on a single conjugated polymer backbone are reported. This copolymer is shown to have CIE coordinates of (0.35,0.34) and a luminance efficiency of 6.2,cd,A,1. The color coordinates of the resulting white-light emission remained extremely stable over a wide range of driving voltages. [source]

    An Artificial Muscle with Lamellar Structure Based on a Nematic Triblock Copolymer,

    ADVANCED MATERIALS, Issue 21 2004
    M.-H. Li
    A muscle-like material with a lamellar structure has been prepared for the first time from a liquid-crystalline triblock copolymer. The material consists of a repeated series of nematic-polymer blocks and conventional rubber blocks. The motor for the contraction is the reversible macromolecular-chain shape change, from stretched to spherical, of the nematic polymer that occurs at the nematic-to-isotropic phase transition. [source]

    High-Performance Polymer Solar Cells of an Alternating Polyfluorene Copolymer and a Fullerene Derivative,

    ADVANCED MATERIALS, Issue 12 2003
    M. Svensson
    Solar cells prepared using the alternating copolymer shown in the Figure blended with a C60 derivative (PCBM) are demonstrated to have a high performance, with a power conversion efficiency of 2.2,% under simulated solar light. The molecular weight of the polymer is low due to limited solubility, and films of the polymer exhibit red-shifted absorption. [source]

    Styrene 4-vinylbenzocyclobutene copolymer for microelectronic applications

    Ying-Hung So
    Abstract Styrene and 4-vinylbenzocyclobutene (vinyl-BCB) random copolymers were prepared by free radical polymerization and studied for suitability as a dielectric material for microelectronic applications. The percentage of vinyl-BCB in the copolymer was varied from 0 to 26 mol % to optimize the physical and mechanical properties of the cured copolymer as well as the cost. Copolymer in which 22 mol % of vinyl-BCB was incorporated along with styrene produced a thermoset polymer which, after cure, did not show a Tg before decomposition at about 350 C. The polymeric material has a very low dielectric constant, dissipation factor, and water uptake. The fracture toughness of the copolymer was improved with the addition of 20 wt % of a star-shaped polystyrene- block -polybutadiene. Blends of the poly(styrene- co -vinyl-BCB) with the thermoplastic elastomer provided material that maintained high Tg of the cured copolymer with only a slight decrease in thermal stability. The crosslinked styrenic polymer and toughened blends possess many properties that are desirable for high frequency-high speed mobile communication applications. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2799,2806, 2008 [source]

    Enhancing electrochromic properties of conducting polymers via copolymerization: Copolymer of 1-(4-fluorophenyl)-2,5-di(thiophen-2-yl)-1H -pyrrole with 3,4-ethylene dioxythiophene,

    Ozlem Turkarslan
    Abstract A copolymer of 1-(4-fluorophenyl)-2,5-di(thiophen-2-yl)-1H -pyrrole (FPTP) with 3,4-ethylene dioxythiophene (EDOT) was electrochemically synthesized and characterized. While poly(FPTP) (P(FPTP)) has only two colors in its oxidized and neutral states (blue and yellow), its copolymer with EDOT has five different colors (purple, red, light gray, green, and blue). Electrochromic devices based on P(FPTP- co -EDOT) and poly(3,4-ethylenedioxythiophene) (PEDOT) were constructed and characterized. The oxidized state of the device shows blue color whereas it shows purple for the reduced state. At several potentials the device has good transparency with green and gray colors. Maximum contrast (,%T) and switching time of the device were measured as 23% and 1.1 s at 555 nm. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4496,4503, 2007 [source]

    Crystal Morphology of Mesoporous Silica Thin Films Synthesized by the Spin-Coating Method Using PEO,PPO,PEO Triblock Copolymer

    Gyeong-Su Park
    Mesoporous thin films on Si substrates with thicknesses of about 460,610 nm have been synthesized by the spin-coating method using a Pluronic EO77PO29EO77 (F68), EO104PO39EO104 (F88), and EO133PO50EO133 (F108) triblock copolymer system. The triblock copolymers were preserved within the synthesized mesoporous thin films. Transmission electron microscopy (TEM) characterization of these films clearly demonstrates that long-range mesostructural ordering strongly depends on the molecular weight of the poly(ethylene oxide),poly(propylene oxide),poly(ethylene oxide) (PEO,PPO,PEO) triblock copolymer, with lower molecular weight producing higher degrees of order. Plane and cross-sectional high-resolution TEM studies coupled with X-ray diffraction (XRD) analysis also show that highly ordered F68 mesoporous silica thin film forms a cubic structure with a lattice spacing a= 6.70 nm. [source]

    Efficient Encapsulation of Plasmid DNA in pH-Sensitive PMPC,PDPA Polymersomes: Study of the Effect of PDPA Block Length on Copolymer,DNA Binding Affinity

    Hannah 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. [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]

    Multi-Responsive Supramolecular Double Hydrophilic Diblock Copolymer Driven by Host-Guest Inclusion Complexation between , -Cyclodextrin and Adamantyl Moieties

    Hao 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]

    New Cyclic Olefin Copolymer for the Preparation of Thermally Responsive Luminescent Films

    Filippo Donati
    Abstract Polymer films with optical properties as indicators to thermal stress were obtained through the controlled dispersion of moderate amounts (,0.1 wt.-%) of the 4,4,-bis(2-benzoxazolyl)stilbene (BBS) dye into a new semicrystalline ethylene-norbornene (E - co - N, N content of 15.3 mol.-%) copolymer characterized by a glass transition temperature (Tg) of about 64,C. All the pristine films showed optical characteristics coming from noninteracting BBS chromophores. In contrast permanent optical changes were detected after film annealing at a T,,,Tg due to the variation of the BBS supramolecular structure. The easy modulation of the optical features of polymer films by thermal perturbations suggests applications as threshold temperature visual indicators in thermoplastic materials. [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]

    A Novel Strategy to Synthesize Double Comb-Shaped Water Soluble Copolymer by RAFT Polymerization

    De-Hui Han
    Abstract Summary: A double comb-shaped water soluble copolymer, poly[poly(ethylene oxide) methyl ether methacrylate]- block -poly(N -isopropylacrylamide)- block -poly[poly (ethylene oxide) methyl ether methacrylate], abbreviated as [P(MA-MPEO)- block -PNIPAM- block -P(MA-MPEO)], with a controlled molecular weight and narrow polydispersity was successively synthesized using a macromonomer technique. The 60Co , irradiation polymerization of MA-MPEO in the presence of dibenzyl trithiocarbonate (DBTTC) at room temperature afforded a polymer, P(MA-MPEO)-SC(S)S-P(MA-MPEO), which was subsequently used as a macro RAFT agent in the RAFT polymerization of N -isopropylacrylamide, and water soluble double comb-shaped copolymers, P(MA-MPEO)- block -PNIPAM- block -P(MA-MPEO), were successfully obtained. Structure of the double comb-shaped copolymer. [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]

    Ordering Behavior of Layered Silicate Nanocomposites with a Cylindrical Triblock Copolymer

    Chung Ho Lee
    Abstract Summary: The ordering behavior of the nanocomposites of organically modified montmorillonite (OMMT) with a cylindrical triblock copolymer of polystyrene- block -poly(ethylene- co -butylene)- block -polystyrene (SEBS) has been investigated by temperature-resolved small-angle X-ray scattering (SAXS) and rheometry. X-Ray diffraction (XRD) confirms that the polymer chains are successfully intercalated with the interlayer gallery of the silicates. The data obtained from the SAXS and rheological measurements show that the addition of OMMT leads to a change in the microphase separation behavior of SEBS in the nanocomposites. The molecular interaction between OMMT and the polystyrene (PS) chains of SEBS decreases the structural perfection of the self-assembling, phase-separated domain structure of the nanocomposites. Rheological data exhibit that the order-order (TOOT) and order-disorder transitions (TODT) of the SEBS/OMMT nanocomposites decrease with the addition of OMMT. The highest elongation at break is obtained at approximately 2% OMMT and its further addition to the mixture leads to decreases in tensile strength and elongation. The change in the storage modulus (G,) of a) SEBS, b) S98M2, c) S95M5, and d) S90M10, as a function of temperature in the range of 150,,,T (C),,,260. [source]

    Crystallization and Ring-Banded Spherulite Morphology of Poly(ethylene oxide)- block -Poly(, -caprolactone) Diblock Copolymer

    Shichun 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]

    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]

    NMR Characterization of Carbazole-Substituted Norbornene Comonomer 9-(Bicyclo[2.2.1.]hept-5-en-2-ylmethyl)-9H -carbazole (BHMCZ) and Poly(ethylene- co -BHMCZ) Copolymer

    Ilpo Mustonen
    Abstract Carbazole-substituted norbornene comonomer 9-(bicyclo[2.2.1.]hept-5-en-2-ylmethyl)-9H -carbazole (BHMCZ) can be copolymerized with ethylene using the [Ph2C(Ind)(Cp)ZrCl2] catalyst and methylaluminoxane (MAO) cocatalyst system. The microstructures of BHMCZ comonomer and of ethylene,BHMCZ copolymer containing 4.6 mol-% BHMCZ units in the chain were characterized by one-dimensional 13C DEPT and two-dimensional homonuclear 1H- 1H COSY and heteronuclear 1H- 13C HXCO NMR spectroscopy. The BHMCZ comonomer appears as endo and exo stereoisomers, which were identified on the basis of chemical shifts, signal multiplicities, and coupling in the 2D NMR spectra. The NMR information on the BHMCZ isomers was used to assist in the determination of the chemical shifts and microstructure of ethylene,BHMCZ copolymer. The NMR analysis of ethylene,BHMCZ copolymer indicated that exo -BHMCZ polymerizes with ethylene slightly more readily than does endo -BHMCZ under the polymerization conditions employed. Isolated segments of exo(2)- exo(5)- exo(6) and endo(2)- exo(5)- exo(6) ethylene-BHMCZ copolymer showing carbon atom numbering. [source]

    Fabrication of Regularly Patterned Microporous Films by Self-Organization of an Amphiphilic Liquid-Crystalline Diblock Copolymer in a Dry Environment

    Dong 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 m 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 and Characterization of Biodegradable Poly(, -caprolactone)-Polyglycolide-Poly(ethylene glycol) Monomethyl Ether Random Copolymer

    Shaobing Zhou
    Abstract Summary: Poly(, -caprolactone)-polyglycolide-poly(ethylene glycol) monomethyl ether random copolymers were synthesized from , -caprolactone (, -CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160,C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, 1H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG. [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]