Showing papers on "Copolymer published in 2000"

Copolymerization of polar monomers with olefins using transition-metal complexes.

Abstract: Transition-metal catalysts long ago made it from the laboratory bench to the polymerization reactor. Indeed, they are being used around the world to make more than 70 million tons of polyethylene and polypropylene a year. Transition-metal catalysts give polyolefin producers unprecedented flexibility in process and polymer design. However, there are still new worlds for catalysts to conquer. One of the most challenging targets is the controlled copolymerization of simple olefins with polar functional monomers. Success in this area would mark a quantum advance in polyolefin field.

Biomimetic synthesis of ordered silica structures mediated by block copolypeptides.

Abstract: In biological systems such as diatoms and sponges, the formation of solid silica structures with precisely controlled morphologies is directed by proteins and polysaccharides and occurs in water at neutral pH and ambient temperature. Laboratory methods, in contrast, have to rely on extreme pH conditions and/or surfactants to induce the condensation of silica precursors into specific morphologies or patterned structures. This contrast in processing conditions and the growing demand for benign synthesis methods that minimize adverse environmental effects have spurred much interest in biomimetic approaches in materials science. The recent demonstration that silicatein-a protein found in the silica spicules of the sponge Tethya aurantia--can hydrolyse and condense the precursor molecule tetraethoxysilane to form silica structures with controlled shapes at ambient conditions seems particularly promising in this context. Here we describe synthetic cysteine-lysine block copolypeptides that mimic the properties of silicatein: the copolypeptides self-assemble into structured aggregates that hydrolyse tetraethoxysilane while simultaneously directing the formation of ordered silica morphologies. We find that oxidation of the cysteine sulphydryl groups, which is known to affect the assembly of the block copolypeptide, allows us to produce different structures: hard silica spheres and well-defined columns of amorphous silica are produced using the fully reduced and the oxidized forms of the copolymer, respectively.

Amphiphilic Block Copolymers: Self-Assembly and Applications

Abstract: Theory of block copolymer self-assembly: Modelling of the self-assembly of block copolymers in selective solvent, (P. Linse) On the origin of the solution behavior of ethyleneoxide containing polymers, (G. Karlstr m). Self-assembly in simple and complex systems: Block copolymers of ethylene oxide and 1,2-butylene oxide, (C. Booth et al.) Self-assembly of block polyelectrolytes, (L. Zhang et al.) Formation of amphiphilic block copolymer micelles in nonaqueous solution, (T. Liu et al.) Structures of amphiphilic block copolymers in their liquid and solid states, (A.J. Ryan et al.) Structural polymorphism of amphiphilic block copolymers in mixtures with water and oil - comparison with solvent-free block copolymers and surfactant systems, (P. Alexandridis et al.) Techniques for the study of self-assembly structure and dynamics: Small-angle scattering studies of block copolymer micelles, micellar mesophases and networks, (K. Mortensen) Fluorescence studies of amphiphilic block copolymers in solution, (R. Zana) Direct-imaging cryo-transmission electron microscopy in the study of colloids and polymer solutions, (M. Goldraich, Y. Talmon) Rheology of transient networks formed by the association of hydrophobically modified water soluble polymers, (T. Annable et al.). Applications of amphiphilic copolymers: Applications of block copolymers, (K. Holmberg) Block copolymers in pharmaceutics, (M. Malmsten) Micelles of amphiphilic block copolymers as vehicles for drug delivery, (A.V. Kabanov, V.Yu. Alakhov) Applications of amphiphilic copolymers in separations, (M. Svensson et al.) Polymeric surfactants as emulsion stabilizers, (R. Pons).

Ordered Deposition of Inorganic Clusters from Micellar Block Copolymer Films

Abstract: A method is presented for generating quasiregular arrays of nanometer-sized noble metal and metal oxide clusters on flat substrates by the use of a polymer template. The approach is of general applicability to other metals and various oxides. In the first step, polymeric micelles with a polar core were generated by dissolution of poly(styrene)-block-poly(2-vinylpyridine) in toluene. These micelles were used as nanocompartments that were loaded with a defined amount of a metal precursor. The metal ions can be reduced in such a way that exactly one elemental or oxidic particle is formed in each micelle, where each particle is of equal size. By dipping a flat substrate into a dilute solution, a monolayer of the micelles was obtained whereby the embedded equally large particles became arranged in a mesoscopic quasihexagonal two-dimensional (2-D) lattice. Exposure to an oxygen plasma allowed removal of the polymer completely, leaving the naked metal particles firmly attached to the substrate in the same quasih...

Polymerized ABA Triblock Copolymer Vesicles

Abstract: The synthesis and the characterization of a poly(2-methyloxazoline)-block-poly(dimethylsiloxane)-block-poly(2-methyloxazoline) (PMOXA−PDMS−PMOXA) triblock copolymer carrying polymerizable groups at both chain ends are described. This copolymer forms vesicular structures in dilute aqueous solution, the size of which can be controlled in the range from 50 nm up to about 500 nm. The methacrylate end groups of the triblock copolymer can be polymerized in the vesicular aggregates using an UV-induced free radical polymerization. Static and dynamic light scattering, scanning electron microscopy, and transmission electron microscopy on both the resulting nanocapsules and their nonpolymerized precursors clearly show that the cross-linking polymerization does not lead to morphological changes in the underlying vesicles. Moreover, due to their cross-linked structure, the nanocapsules are shape persistent, thus maintaining their integrity even after their isolation from the aqueous solution.

Effects of block architecture and composition on the association properties of poly(oxyalkylene) copolymers in aqueous solution

Abstract: A block copolymer of hydrophilic poly-(ethylene oxide) and a hydrophobic poly(alkylene oxide) can associate in dilute aqueous solution to form micelles. The results of recent investigations of the micellisation behaviour and micelle properties of such copolymers are described. Copolymers of ethylene oxide with propylene oxide, 1,2-butylene oxide or styrene oxide are considered, including aspects of their preparation. Experimental methods for determination of critical conditions for micellisation, micelle association number and spherical-micelle radius are summarised. Effects of temperature, composition, block length and block architecture (diblock, triblock and cyclic-diblock) are described and, where possible, related to the predictions of theory. Brief consideration is given to the dynamics of micelle formation/dissociation, to cylindrical micelles, and to effects of added salts.

Shell Cross-Linked Nanoparticles Containing Hydrolytically Degradable, Crystalline Core Domains

Abstract: Shell cross-linked knedel-like nanoparticles (SCKs) possessing an amphiphilic core−shell morphology consisting of a cross-linked shell and a hydrolytically degradable, crystalline core domain were synthesized from poly(e-caprolactone)-b-poly(acrylic acid) (PCL-b-PAA) amphiphilic diblock copolymers via a two-step process: self-assembly of PCL-b-PAA into polymer micelles followed by cross-linking of the hydrophilic shell layer via condensation reactions between the carboxylic acid functionalities of PAA and the amine groups of 2,2‘-(ethylenedioxy)bis(ethylamine). PCL-b-PAA was prepared from the selective hydrolysis of a poly(e-caprolactone)-b-poly(tert-butyl acrylate) (PCL-b-PtBA) precursor, which was synthesized by ring opening polymerization (ROP) of e-caprolactone (e-CL) followed by atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA). Selective hydrolysis of the tert-butyl ester groups of the PtBA block by reaction with trimethylsilyl iodide (TMSI), followed by reaction with aqueous...

Phase Behavior of a Block Copolymer in Solvents of Varying Selectivity

Abstract: The effect of the thermodynamic selectivity of a solvent on the self-assembly of a styrene−isoprene (SI) diblock copolymer with block molecular weights of 1.1 × 104 and 2.1 × 104 g/mol is investigated. We explore the phase behavior from the melt state to dilute solution in solvents that are of varying selectivities for the two blocks. Bis(2-ethylhexyl) phthalate (DOP) is a neutral good solvent for SI. Di-n-butyl phthalate (DBP) and diethyl phthalate (DEP) are good solvents for PS but marginal and poor, respectively, for PI. Tetradecane (C14) is utilized as a complementary solvent that is good for PI but poor for PS. Small-angle X-ray scattering (SAXS) and static birefringence are used to locate and identify order−order (OOT) and order−disorder transitions (ODT). Dynamic and static light scattering were used to characterize the dilute solution micellar behavior. The neat polymer forms the gyroid (G1) morphology at low temperature, an OOT to hexagonal-packed cylinders (C1) occurs at 185 °C, and the ODT is l...

Self-Assembly of Organometallic Block Copolymers: The Role of Crystallinity of the Core-Forming Polyferrocene Block in the Micellar Morphologies Formed by Poly(ferrocenylsilane-b-dimethylsiloxane) in n-Alkane Solvents

Abstract: The organometallic−inorganic diblock copolymer poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFDMS-b-PDMS) with a 1:6 block ratio unexpectedly forms long rodlike micelles rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared at or near ambient temperature. The cylindrical structures represent the thermodynamically preferred morphology and consist of an iron-rich PFDMS core and a corona of PDMS. The length of the micelles can be varied from 70 nm to 10 μm by altering the method of sample preparation. In addition, the dimensions of the micellar core can be controlled through variations in the length of the PFDMS block, which is achieved by altering the molecular weight of the diblock copolymer while maintaining a constant block ratio. In contrast, when micelles are formed above the Tm of PFDMS (ca. 120−145 °C), spherical aggregates are formed, which suggests that crystallization of the core polymer is the driving force for the formation of wor...

Semiconducting Diblock Copolymers Synthesized by Means of Controlled Radical Polymerization Techniques

Abstract: A donor−acceptor, rod−coil diblock copolymer has been synthesized with the objective of enhancing the photovoltaic efficiency of the PPV−C60 (PPV = poly(p-phenylenevinylene)) system by the incorporation of both components in a molecular architecture that is self-structuring through microphase separation. Diblock copolymers were obtained by using an end-functionalized rigid-rod block of poly(2,5-dioctyloxy-1,4-phenylenevinylene) as a macroinitiator for the nitroxide-mediated controlled radical polymerization of a flexible poly(styrene-stat-chloromethylstyrene) block. The latter block was subsequently functionalized with C60 through atom-transfer radical addition. In a spin-cast film of the final diblock copolymer, the luminescence from PPV is strongly quenched, indicating efficient electron transfer to C60. Under suitable conditions, solution-cast films of these diblock copolymers exhibit micrometer-scale, honeycomb-like patterns of holes.

Overcoming Interfacial Interactions with Electric Fields

Abstract: Electric fields have been shown to orient nanoscopic domains laterally in thin copolymer films effectively. To achieve an orientation normal to the surface, interfacial interactions impose a barrier. Using asymmetric diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA) having cylindrical microdomains, a threshold electric field strength Et was found above which complete orientation of the cylindrical domains was achieved. This threshold field strength was independent of film thickness (for films ∼10−30 μm thick) and could be described by the difference in interfacial energies of the components. At field strengths slightly below Et a coexistence of the domains parallel and perpendicular to the electrode surface was found which is consistent with the introduction of defects via undulations in the structure as one proceeds away from the surface.

Tunable Block Copolymer/Homopolymer Photonic Crystals

Abstract: Interest in the photonic properties of dielectrically struc-tured materials is growing rapidly. This is fueled by the potential application of such materials in a broad range of fields. Much recent work has focused on lithographically fabricated photonic materials, [1,2] and on self-assembled colloidal crystals [3,4] and inverse opal structures. [5±7] The former need to be fabricated on small-area flat surfaces, the latter tend to have long timescales inherent in the fabrication and both have limited tunability with respect to the precursor materials. Our recent work [8,9] has shown that self-assembled block copolymer systems can exhibit a one-dimensionally periodic lamellar structure with component domains having widths large enough (l/4n) to act as visible light photonic materials. Their use in photonics would bring many advantages in terms of materials properties, process-ability, as well as cost, and would enable the fabrication of large-area conformable photonic materials. In this communication we show that multilayer photonic crystals active within a broad range of wavelengths in the visible spectrum can easily be produced from a simple system comprised of a block copolymer and two homopolymers. Ternary blends of a poly(styrene-b-isoprene) (S/I) di-block copolymer, polystyrene, and polyisoprene were solution cast from cumene. As the samples begin to dry they selectively reflect light, giving the appearance of green or red color. After drying, each sample showed a single well-defined peak in reflectivity in the visible wavelength range (350±600 nm) and a corresponding drop in the transmission profile. This implies that the reflection was fairly efficient and that the color observed in the samples was not due to significant absorption. In Figure 1a, we show typical reflec-tivity curves for several blend samples. The relative width of the reflectivity peaks (or transmission dips), Dl/l, varies approximately from 0.15 to 0.25, widening as the fraction of homopolymer in the blend increases. The wavelength of the reflectivity peak versus the homopolymer composition is plotted in Figure 1b. There is a monotonic increase in the peak reflective wavelength with the fraction of homopoly-mer. Scanning electron microscopy (SEM) of the samples confirmed that a lamellar morphology was present in the samples , with typical grain sizes of the order of several micro-meters. The backscattered electron imaging (BEI) image of a sample containing 40 % homopolymer is shown in Figure 2a. The bright regions correspond to the OsO 4 stained polyisoprene domains and the dark regions are the un-stained polystyrene. The lamellar repeat from the …

Reconstitution of Channel Proteins in (Polymerized) ABA Triblock Copolymer Membranes

Abstract: A new class of mechanically stable block copolymer protein hybrid materials: Giant freestanding membranes with a thickness of 10 nm were prepared from polymerizable amphiphilic triblock copolymers in which, despite their extreme thickness, it was possible to reconstitute channel proteins. The proteins remained functional in the completely artificial surrounding even after polymerization of the membranes, as revealed by conductance measurements. These polymerâEuro"protein hybrid materials possess great potential for applications in the area of diagnostics, sensor technology, protein crystallization, and even drug delivery.

Reactive Block Copolymers for Modification of Thermosetting Epoxy

Abstract: Block copolymers incorporating epoxy-reactive functionality in one block have been studied as modifiers for model epoxy resins. As observed previously with nonreactive poly(ethylethylene)-b-poly(ethylene oxide) (OP) copolymers, reactive poly(epoxyisoprene)-b-polybutadiene (BIxn) copolymers and poly(methyl acrylate-co-glycidyl methacrylate)-b-polyisoprene (MG-I) copolymers form ordered microstructures in blends with epoxy precursors as evidenced by small-angle X-ray scattering and transmission electron microscopy. Like OP copolymers, both types of reactive copolymer remain well-dispersed within the epoxy matrix during cure. Additionally, DSC and solubility studies suggest that these copolymers can react with the curing epoxy resin to form covalent linkages between the copolymeric microstructures and the cross-linked epoxy resin. The capability of these types of copolymers to template epoxy resin is proposed to arise from a combination of (1) the miscibility of one block with the epoxy components well into ...

Synthesis and Luminescence Properties of Novel Eu-Containing Copolymers Consisting of Eu(III)−Acrylate−β-Diketonate Complex Monomers and Methyl Methacrylate

Abstract: Luminescent Eu-containing copolymers were synthesized through the copolymerization of Eu−complex monomers containing β-diketones with methyl methacrylate and characterized by FT-IR, UV−vis, XPS, GPC, TGA, and DSC. All these Eu copolymers are fully soluble in common organic solvents and can be cast into transparent, uniform, thin films with good mechanical flexibility and thermal stability. The Eu−copolymer luminophores exhibited intense red light at 615 nm under UV excitation at room temperature, which is attributed to the 5D0→7F2 transition of Eu(III) ions. The luminescence intensities, lifetimes and monochromaticities, η(5D0→7F2/5D0→7F1), of the Eu−copolymers are much higher than that of the corresponding Eu−complex monomers as well as Eu−complex/PMMA blends. Energy transfer processes and microenvironment effects were found to contribute to the improvement of the luminescence properties of the Eu−copolymers. A study of the dependence of emission intensities of the Eu−copolymers on the Eu content showed ...

Synthesis and Characterization of Vinyl Polymer−Silica Colloidal Nanocomposites

Abstract: Colloidal dispersions of polymer−silica nanocomposite particles were synthesized in high yield by homopolymerizing 4-vinylpyridine (4VP) in the presence of an ultrafine silica sol using a free-radical initiator in aqueous media at 60 °C. Copolymerization of 4VP with methyl methacrylate and styrene also produced colloidally stable nanocomposite particles, in some cases for comonomer feeds containing as little as 6 mol % 4VP. However, homopolymerization of styrene or methyl methacrylate in the presence of the silica sol did not produce nanocomposite particles in control experiments. Thus a strong acid−base interaction between the silica sol and the (co)polymer appears to be essential for nanocomposite formation. Transmission electron microscopy studies confirmed the presence of the ultrafine silica sols within the nanocomposite particles, which typically exhibited “currant-bun” particle morphologies. This is in contrast to the “raspberry” particle morphologies previously reported for conducting polymer−sili...

Morphology of Ultrathin Supported Diblock Copolymer Films: Theory and Experiment

Abstract: An analysis of the morphological behavior of substrate-supported diblock copolymer films for thicknesses t below the equilibrium period L0 of the copolymer is presented. Substrate-supported films generally exhibit dissimilar interactions between the copolymer block components and the free and substrate surfaces. Accordingly, in this study, self-consistent-field calculations that incorporate asymmetric surface energetics were used to assess equilibrium film morphologies. Phase diagrams were constructed as a function of film thickness, surface interaction energies, the segmental interaction, and the chain length. In conjunction, experiments were conducted on a series of polystyrene-b-poly(n-alkyl methacrylate) copolymer films supported by silicon substrates. These employed a novel atomic force microscopy technique that allowed for the precise tracking of morphology as a function of film thickness. Comparison of the experimental results and calculations revealed several common trends. In particular, hybrid m...

Surface Modification of Fluoropolymers via Molecular Design

Abstract: Fluoropolymer surfaces with new and specific functionalities, such as metal-free conductivity, biocompatability, and bondability to metals, can be obtained through the intelligent choice of functional monomers for graft copolymerization on pre-activated fluoropolymer surfaces, as highlighted in this review. The Figure shows a gold/fluoropolymer laminate held together by crosslinked glycidyl methacrylate polymer grafted on both surfaces.

Controlled radical copolymerization of styrene and maleic anhydride and the synthesis of novel polyolefin‐based block copolymers by reversible addition–fragmentation chain‐transfer (RAFT) polymerization

Abstract: Reversible addition–fragmentation chain transfer (RAFT) was applied to the copolymerization of styrene and maleic anhydride. The product had a low polydispersity and a predetermined molar mass. Novel, well-defined polyolefin-based block copolymers were prepared with a macromolecular RAFT agent prepared from a commercially available polyolefin (Kraton L-1203). The second block consisted of either polystyrene or poly(styrene-co-maleic anhydride). Furthermore, the colored, labile dithioester moiety in the product of the RAFT polymerizations could be removed from the polymer chain by UV irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3596–3603, 2000

The preparation of t-butyl acrylate, methyl acrylate, and styrene block copolymers by atom transfer radical polymerization: Precursors to amphiphilic and hydrophilic block copolymers and conversion to complex nanostructured materials

Abstract: Atom transfer radical polymerization conditions with copper(I) bromide/pentamethyldiethylenetriamine (CuBr/PMDETA) as the catalyst system were employed for the polymerization of tert-butyl acrylate, methyl acrylate, and styrene to generate well-defined homopolymers, diblock copolymers, and triblock copolymers. Temperature studies indicated that the polymerizations occurred smoothly in bulk at 50 °C. The kinetics of tert-butyl acrylate polymerization under these conditions are reported. Well-defined poly-(tert-butyl acrylate) (PtBA; polydispersity index = 1.14) and poly(methyl acrylate) (PMA; polydispersity index = 1.03) homopolymers were synthesized and then used as macroinitiators for the preparation of PtBA-b-PMA and PMA-b-PtBA diblock copolymers in bulk at 50 °C or in toluene at 60 or 90 °C. In toluene, the amount of CuBr/PMDETA relative to the macroinitiator was important; at least 1 equiv of CuBr/PMDETA was required for complete initiation. Typical block lengths were composed of 100-150 repeat units per segment. A triblock copolymer, composed of PtBA-b-PMA-b-PS (PS = polystyrene), was also synthesized with a well-defined composition and a narrow molecular weight dispersity. The tert-butyl esters of PtBA-b-PMA and PtBA-b-PMA-b-PS were selectively cleaved to form the amphiphilic block copolymers PAA-b-PMA [PAA = poly(acrylic acid)] and PAA-b-PMA-b-PS, respectively, via reaction with anhydrous trifluoroacetic acid in dichloromethane at room temperature for 3 h. Characterization data are reported from analyses by gel permeation chromatography; infrared, 1 H NMR, and 13 C NMR spectroscopies; differential scanning calorimetry; and matrix-assisted, laser desorption/ionization time-of-flight mass spectrometry. The assembly of the amphiphilic triblock copolymer PAA 90 -b-PMA 80 -b-PS 98 within an aqueous solution, followed by conversion into stable complex nanostructures via crosslinking reactions between the hydrophilic PAA chains comprising the peripheral layers, produced mixtures of spherical and cylindrical topologies. The visualization and size determination of the resulting nanostructures were performed by atomic force microscopy, which revealed very interesting segregation phenomena.

Crystal Design of Barium Sulfate using Double-Hydrophilic Block Copolymers.

Abstract: Peach, peanut, fiber, and flower (see picture) crystal morphologies are achieved from the precipitation of simple minerals in the presence of specifically adsorbing polymers. These crystal design effects are illustrated using BaSO(4) and double-hydrophilic block copolymers, the latter featuring carboxylate, sulfonate, phosphonate, and aspartic acid groups.

“Living” Free Radical Photopolymerization Initiated from Surface-Grafted Iniferter Monolayers

Abstract: A method for chemically modifying a surface with grafted monolayers of initiator groups, which can be used for a “living” free radical photopolymerization, is described. By using “living” free radical polymerizations, we were able to control the length of the grafted polymer chains and therefore the layer thickness up to ∼100 nm. Also, single-layer grafted block copolymers were obtained by subsequent polymerizations of styrene and methyl methacrylate monomers. The surface-grafted polymer and block copolymer layers were evidenced by direct imaging methods (transmission and scanning electron microscopy) and by indirect surface characterization methods (contact angle measurements, SFM, XPS, and IR). The ability to control the thickness of the grafted polymer as well as the synthesis of a grafted block copolymer layer in a well-defined manner affirms the “living” character of the surface-initiated free radical photopolymerization.

Solution behavior of poly(styrene)-block-poly(2-vinylpyridine micelles containing gold nanoparticles

Abstract: Formation and structural transformation of inverse poly(styrene)-block-poly(2-vinylpyridine) micelles whose polyvinylpyridine core was loaded with HAuCl4 or with elementary gold nanoclusters was studied by combined static and dynamic light scattering. A transformation in the morphology from spherical particles (small Rg/Rh ratio) to large anisomeric objects (large Rg/Rh ratio) was observed by decreasing the concentration of the block copolymer below the critical micelle concentration. At this point, the polymer chains are molecularly dispersed and no longer able to prevent uncontrolled growth of the gold nanoclusters.