Search

The carbon content of mesostructured organic-inorganic hybrid material of a cylindrical block copolymer template of poly(2-vinylpyridine)-block-poly(allyl methacrylate) (P2VP-b-PAMA) and ammonium paramolybdate (APM) could be reduced by thermal depolymerization. By calcination in vacuo at 320 °C the PAMA core can be completely removed while the remaining P2VP brush preserves the mesostructure. The P2VP-APM composite can then be carburized in-situ to MoOxCy in a second pyrolysis step without any additional carbon source but P2VP. The molybdenum oxycarbide nanotubes obtained, form hierarchically porous non-woven structures, which were tested as catalyst in the decomposition of NH3. They proved to be catalytically active at temperatures above 450 °C. The activation energy was estimated from an Arrhenius Plot to be 127 kJ·mol–1.

In this paper, preparation method and actuation properties of an innovative composite membrane composed of thermo- and pH-responsive poly(N-isopropylacrylamide-co-acrylic acid) fibers (average diameter ≈ 905 nm) embedded within a passive thermoplastic polyurethane (TPU) matrix at different angles with degree of alignment as high as 98% are presented. The composite membrane has a gradient of TPU along the thickness. It has the capability of temperature- and pH-dependent direction-, and size-controlled actuation in few minutes. The stresses generated at the responsive fiber and nonresponsive matrix provide actuation, whereas the angle at which fibers are embedded in the matrix controls the actuation direction and size. The temperature has no effect on actuation and actuated forms at pH 7 and above, whereas the size of the actuated forms can be controlled by the temperature at lower pH. The membranes are strong enough to reversibly lift and release ≈426 times weight of their own mass (2.47 g metal ring is lifted by a 5.8 mg membrane). Soft actuators are of interest as smart scaffolds, robotics, catalysis, drug release, energy storage, electrodes, and metamaterials.

A new route for the preparation of enzymatically degradable amphiphilic conetworks (APCNs) based on unsaturated polyesters by radical ring-opening copolymerization of vinylcyclopropane (VCP) with cyclic ketene acetal (CKA) is presented in this article. In the first step, the unsaturated biodegradable polyesters with random distribution of cross-linkable double bonds and degradable ester units were prepared by radical ring-opening copolymerization of VCP and CKA such as 2-methylene-4-phenyl-1,3-dioxolane (MPDO). Very similar reactivity ratios (rVCP = 0.23 ± 0.08 and rMPDO = 0.18 ± 0.02), unimodal gel permeation chromatography (GPC) curves and 2D NMR technique (heteronuclear multiple bond correlation, HMBC) showed the formation of random copolymers with unsaturation and ester units. The unsaturated units were used for cross-linking by radical polymerization with a hydrophilic macromonomer (oligo(ethylene glycol) methacrylate, OEGMA) in a second step for the formation of enzymatically degradable amphiphilic conetworks (APCNs). Enzymatic degradability was studied using Lipase from Pseudomonas cepacia. Due to the hydrophilic (HI) and hydrophobic (HO) microphase separation, the APCNs showed swelling in both water and organic solvents with different optical properties. The method provides an interesting route for making functional biodegradable APCNs using radical chemistry in the future by choosing appropriate vinyl comonomers.

The chemical structure and high aspect ratio of carbon nanotubes (CNTs) give rise to numerous exceptional physical properties but are also the origin for their intrinsic tendency to agglomerate. Since the full potential of CNTs is harnessed in homogeneous dispersions, e.g. in a polymer matrix, bundling of CNTs must be suppressed by compatibilizing unfavorable interfaces. We present a robust, noncovalent functionalization of multiwalled CNTs via physical grafting of polystyrene-block-polyethylene-block-poly(methyl methacrylate) (SEM) triblock terpolymers to the CNT surface in organic media. In an ultrasound-assisted approach at ambient temperature, the polyethylene (PE) middle block of SEM strongly adsorbs to the CNTs surface, yielding long-term stable dispersions of well-separated 1D hybrids with up to 3 wt % CNT content. Importantly, the strong affinity of PE toward CNTs prevents polymer desorption irrespective of the solvent conditions. The incompatible polystyrene (PS) and poly(methyl methacrylate) (PM...

Ease of catalyst separation from reaction mixtures represents a significant advantage in heterogeneous photocatalytic wastewater treatment. However, the activity of the catalyst strongly depends on its surface-to-volume ratio. Here, we present an approach based on cylindrical polybutadiene- block -poly(2-vinylpyridine) polymer brushes as template, which can be simultaneously loaded with zinc oxide (ZnO) and gold (Au) nanoparticles. Pyrolytic template removal of the polymer yields in mesostructured ZnO/Au composites, showing higher efficiencies in the photocatalytic degradation of ciprofloxacin and levofloxacin (generic antibiotics present in clinical wastewater) as compared to neat mesostructured ZnO. Upscaling of the presented catalyst is straightforward promising high technical relevance.

Polymer-Nanorohrchen mit eingeschlossenen Goldnanopartikeln wurden uber den “Tubes by Fiber Templates”(TUFT)-Prozess hergestellt und als Teebeutel-ahnliches Katalysatorsystem verwendet. Dazu wurden zunachst Poly(L-lactid)-stabilisierte Goldnanopartikel synthetisiert und mit freiem Poly(L-lactid) zu Komposit-Nanofasern elektrogesponnen. Anschliesend wurde das Faservlies aus der Gasphase mit Poly(p-xylylen) beschichtet, und die inneren Templatfasern wurden durch Pyrolyse entfernt. Die so hergestellten Polymer-Rohrchen enthielten immobilisierte Goldnanopartikel und zeigten eine hohe katalytische Aktivitat bezuglich der hydrolytischen Oxidation von Dimethylphenylsilan sowie der entsprechenden Alkoholyse mit n-Butanol. Das makroskopische Rohrchenvlies konnte zur Katalyse analog zu einem Teebeutel verwendet werden und zeigte eine hervorragende Wiederverwendbarkeit.

Gold-containing polymer nanotubes, which showed both catalytic activity and resistance to leaching, were prepared by the "tubes by fiber templates" (TUFT) process. For this purpose, electrospun polymer nonwovens with incorporated poly(L-lactide)-stabilized gold nanoparticles were coated with poly(p-xylylene) by the chemical vapor deposition process, and then the inner fiber templates were removed. The resulting polymer tubes carried encapsulated gold nanoparticles which were shown to be immobilized and featured pronounced catalytic activity towards the hydrolytic oxidation of dimethylphenylsilane and the alcoholysis of dimethylphenylsilane with n-butanol. The macroscopic nonwovens could be used as tea-bag-like catalyst systems and showed excellent reusability.

Living Micrococcus luteus (M. luteus) and Escherichia coli (E. coli) are encapsulated in poly(vinyl alcohol), poly(vinylpyrrolidone), hydroxypropyl cellulose, and gelatin by high-temperature spray drying. The challenge is the survival of the bacteria during the standard spray-drying process at temperatures of 150 °C (M. luteus) and 120 °C (E. coli). Raman imaging and transmission electron microscopy indicate encapsulated bacteria in hollow composite microparticles. The versatility of the spray-dried polymer bacteria microparticles is successfully proved by standard polymer solution-processing techniques such as electrospinning, even with harmful solvents, to water-insoluble polyacrylonitrile, polystyrene, poly(methyl methacrylate), and poly(vinyl butyrate) nanofiber nonwovens, which opens numerous new opportunities for novel applications.

Several hundred grams of Janus nanoparticles (d ≈ 40 nm) were synthesized from triblock terpolymers as compatibilizers for blending of technologically relevant polymers, PPE and SAN, on industry-scale extruders. The Janus nanoparticles (JPs) demonstrate superior compatibilization capabilities compared to the corresponding triblock terpolymer, attributed to the combined intrinsic properties, amphiphilicity and the Pickering effect. Straightforward mixing and extrusion protocols yield multiscale blend morphologies with "raspberry-like" structures of JPs-covered PPE phases in a SAN matrix. The JPs densely pack at the blend interface providing the necessary steric repulsion to suppress droplet coagulation during processing. We determine the efficiency of JP-compatibilization by droplet size evaluation and find the smallest average droplet size of d ≈ 300 nm at 10 wt % of added compatibilizer, whereas at 2 wt %, use of JPs is most economic with reasonable small droplets and narrow dispersity. In case of excess JPs, rheological properties of the system is changed by a droplet network formation. The large-scale synthesis of JPs, the low required weight fractions and their exceptional stability against extensive shear and temperature profiles during industrial extrusion process make JP promising next generation compatibilizers.

Heterogeneous catalysis with supported nanoparticles (NPs) is a highly active field of research. However, the efficient stabilization of NPs without deteriorating their catalytic activity is challenging. By combining top-down (coaxial electrospinning) and bottom-up (crystallization-driven self-assembly) approaches, we prepared patchy nonwovens with functional, nanometer-sized patches on the surface. These patches can selectively bind and efficiently stabilize gold nanoparticles (AuNPs). The use of these AuNP-loaded patchy nonwovens in the alcoholysis of dimethylphenylsilane led to full conversion under comparably mild conditions and in short reaction times. The absence of gold leaching or a slowing down of the reaction even after ten subsequent cycles manifests the excellent reusability of this catalyst system. The flexibility of the presented approach allows for easy transfer to other nonwoven supports and catalytically active NPs, which promises broad applicability.

We introduce a modular route for the synthesis of well-defined ABC miktoarm star terpolymers. To this aim, the synthesis of a 1,1-diphenylethylene derivative bearing a protected alkyne function (1-[(4-(tert-butyldimethylsilyl)ethynyl)phenyl]-1-phenylethylene) was developed. This compound was for the first time employed in sequential anionic polymerization to readily prepare alkyne mid-functionalized diblock copolymers with polybutadiene as first and a poly(alkyl methacrylate) (poly(tert-butyl methacrylate), poly(N,N-dimethylaminoethyl methacrylate)) as second block. For the third arm controlled radical polymerization methods (polystyrene, poly(tert-butyl methacrylate), poly(N,N-dimethylaminoethyl methacrylate)) and anionic ring-opening polymerization (poly(ethylene oxide)) were used to separately prepare homopolymers with an azido function. Afterward, azide–alkyne Huisgen cycloaddition was successfully employed to synthesize a library of ABC miktoarm star terpolymers with different molecular weights and c...

We present a straightforward approach to well-defined 1D patchy particles utilizing crystallization-induced self-assembly. A polystyrene- block -polyethylene- block -poly(methyl methacrylate) (PS- b -PE- b -PMMA) triblock terpolymer is cocrystallized in a random fashion with a corresponding polystyrene- block -polyethylene- block -polystyrene (PS- b -PE- b -PS) triblock copolymer to yield worm-like crystalline-core micelles (wCCMs). Here, the corona composition (PMMA/PS fraction) can be easily adjusted via the amount of PS- b -PE- b -PMMA triblock terpolymer in the mixture and opens an easy access to wCCMs with tailor-made corona structures. Depending on the PMMA fraction, wCCMs with a mixed corona, spherical PMMA patches embedded in a continuous PS corona, as well as alternating PS and PMMA patches of almost equal size can be realized. Micelles prepared by cocrystallization show the same corona structure as those prepared from neat triblock terpolymers at identical corona composition. Thus, within a certain regime of desired corona compositions the laborious synthesis of new triblock terpolymers for every composition can be circumvented.

Double hydrophilic stimuli-responsive star block copolymers with poly(2-(dimethylamino)ethyl methacrylate) (PDMA) inner blocks and poly(2-(diethylamino)ethyl methacrylate) (PDEA) outer blocks were synthesized using ATRP. Different multifunctional initiators based on sugar scaffolds were employed in a core-first approach with sequential polymerization of both blocks yielding stars with 4 and 6 arms, respectively, and varying length of the PDEA outer block. The star block copolymers show pH- and temperature-responsive aggregation as revealed by dynamic light scattering and turbidimetry. The impact of pH, PDEA block length and arm number on the gelation behavior was investigated by tube inversion and rheology.

We present the synthesis of dual-responsive (pH and temperature) magnetic core-shell nanoparticles utilizing the grafting-from approach. First, oleic acid stabilized superparamagnetic maghemite (γ-Fe(2)O(3)) nanoparticles (NPs), prepared by thermal decomposition of iron pentacarbonyl, were surface-functionalized with ATRP initiating sites bearing a dopamine anchor group via ligand exchange. Subsequently, 2-(dimethylamino)ethyl methacrylate (DMAEMA) was polymerized from the surface by ATRP, yielding dual-responsive magnetic core-shell NPs (γ-Fe(2)O(3)@PDMAEMA). The attachment of the dopamine anchor group on the nanoparticle's surface is shown to be reversible to a certain extent, resulting in a grafting density of 0.15 chains per nm(2) after purification. Nevertheless, the grafted NPs show excellent long-term stability in water over a wide pH range and exhibit a pH- and temperature-dependent reversible agglomeration, as revealed by turbidimetry. The efficiency of γ-Fe(2)O(3)@PDMAEMA hybrid nanoparticles as a potential transfection agent was explored under standard conditions in CHO-K1 cells. Remarkably, γ-Fe(2)O(3)@PDMAEMA led to a 2-fold increase in the transfection efficiency without increasing the cytotoxicity, as compared to polyethyleneimine (PEI), and yielded on average more than 50% transfected cells. Moreover, after transfection with the hybrid nanoparticles, the cells acquired magnetic properties that could be used for selective isolation of transfected cells.

The synthesis of galactose-displaying core-shell nanospheres exhibiting both fluorescent and magnetic properties by grafting a glycocopolymer consisting of 6-O-methacryloylgalactopyranose (MAGal) and 4-(pyrenyl)butyl methacrylate (PyMA) onto magnetic silica particles via thiol-ene chemistry is reported. Magnetization measurements indicated that neither the encapsulation of the iron oxide particles into silica nor the grafting of the glycocopolymer chains had a significant influence on the superparamagnetic properties. This not only simplifies the purification of the particles but may facilitate the use of the particles in applications such as hyperthermia or magnetic resonance imaging (MRI). Furthermore, the hydrophilic glycopolymer shell provided solubility of the particles in aqueous medium and enabled the uptake of the particles into the cytoplasm and nucleus of lung cancer cells via carbohydrate-lectin recognition effects.

Aqueous solutions of a double responsive P2VP62-b-PEO452-b-P(GME36-co-EGE36) triblock terpolymer were investigated by means of small-angle neutron scattering (SANS) in order to derive information about structural changes going along with the temperature triggered gel-sol-gel transition at pH = 7, and the sol-gel transition at pH = 3.5, respectively, observed by rheology. SANS measurements on dilute samples at different pH and temperature confirmed the formation of core-shell-corona micelles under conditions, where only one of the outer blocks is insoluble. In addition, temperature-dependent scattering experiments were performed for higher volume fractions, that is, the concentration range where hydrogels were formed. This allowed us to identify the structural transitions, being responsible for the gel-sol-gel transition at pH = 7, and the structure of the gel phase formed at low pH and elevated temperatures.

A combination of anionic polymerization, atom transfer radical polymerization (ATRP) and “click” chemistry was used to construct trishydrophilic ABC triblock terpolymers composed of a pH-sensitive A block, a water-soluble B block and two different thermo-sensitive C blocks without any block sequence limitation problems. First, an azido end-functionalized poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO-N3) diblock copolymer was synthesized by anionic polymerization. In a second step, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) were synthesized via ATRP using an alkyne functionalized initiator. The resulting polymers were attached to the P2VP-b-PEO-N3 diblock copolymer using the 1,3-dipolar Huisgen cycloaddition (“click” chemistry). For the “click” step, P2VP-b-PEO-N3 diblock copolymers with either an azidoacetyl or a 2-azidoisobutyryl group were tested. In the latter case, however, a side reaction involving the cleavage of the formed “click” product via nucleophilic substitution occurred, preventing a permanent attachment of PDMAEMA or POEGMA to the P2VP-b-PEO-N3 diblock copolymer. Finally, P2VP-b-PEO-b-POEGMA (with POEGMA=P(MEO2MA-co-MEO8.5MA)) and P2VP-b-PEO-b-PDMAEMA triblock terpolymers were successfully synthesized and used to construct stimuli-responsive hydrogels. A concentrated solution of P2VP56-b-PEO370-b-P[(MEO2MA)89-co-(MEO8.5MA)7] showed a gel–sol–gel transition at pH 7 upon temperature increase, whereas in the case of P2VP56-b-PEO370-b-PDMAEMA70, a gel–sol or a weak gel–strong gel transition was observed, depending on the applied pH. Finally, the addition of trivalent hexacyanocobaltate(III) ions to the P2VP56-b-PEO370-b-PDMAEMA70 solution induced an upper critical solution temperature for the PDMAEMA block, which led to gel formation. This allows for the construction of light-sensitive hydrogels, utilizing the photo-aquation of hexacyanocobaltate(III) ions.

Thermoreversible hydroferrogels (FGs) have been prepared via gelation of aqueous maghemite ferrofluids (FFs) using the triblock copolymer Pluronic P123 as gelator. In the investigated concentration range of 28-42 wt % P123, long-term stable homogeneous FGs can be prepared from FFs with a maximum maghemite content of 14 wt %. For higher FF concentrations up to 29 wt %, however, homogeneous FGs were formed only for gelator contents up to ca. 33 wt %. A combination of rheology and μ-DSC was applied as an alternative method to construct the P123 phase diagram, without the need for visual methods or scattering techniques. Using this procedure, we could show that maghemite nanoparticles can be effectively templated by the cubic and hexagonal P123 mesophases in a concentration range of 33-38 wt % P123 and FF concentrations up to 14 wt %, respectively. Most importantly, the phase behavior and the corresponding phase-transition temperatures of P123 were not significantly altered. As a result, the FGs show a reversible temperature-triggered transition from a cubic hard gel to a hexagonal gel, which is linked with a softening of the gel. Furthermore, this concept can be applied to template cobalt ferrite nanoparticle effectively, too. Magnetization experiments revealed that the superparamagnetic behavior of the maghemite nanoparticles, which show a Néel type relaxation, is not altered in the corresponding FGs. In contrast, FGs based on blocked cobalt ferrite nanoparticles show a hysteretic behavior, which indicates a strong mechanical coupling between the P123 mesophase and the magnetic nanoparticles.

We report on the synthesis and characterization of linear and star-shaped poly(N,N-diethylaminoethyl methacrylate) (PDEA). The synthesis was accomplished by Atom Transfer Radical Polymerization (ATRP) via a core-first approach using sugar-based multifunctional initiators. The investigation of the solution properties in water shows that PDEA is both pH- and temperature-responsive, analogous to the behavior of poly(N,N-dimethylaminoethyl methacrylate) (PDMA). In literature, PDEA is frequently referred to as being only pH-sensitive. The critical pH values for the aggregation are close to the apparent pKa values in all cases, i.e. a high charge density is necessary to keep the polymers soluble. The cloud points show a strong dependence on the pH value of the solution but no dependence on either molecular weight or architecture. Thus, the two polymers differ only quantitatively, as PDEA has cloud points about 40 K lower than PDMA and critical pH values which are 1.5–2 units lower than PDMA.

The synthesis of star-shaped polymers, which are threaded regularly along a common backbone, is described. Thus, two different approaches for preparation of so-called pearl necklace polymers (synonyms: multigraft copolymers, barbwire or centipedes polymers, multiple dumbbells or star-oligomers) are presented. Poly(ethylene oxide) (PEO) was used as a thread and poly(dimethylaminoethyl methacrylate) (PDMAEMA) stars were used as pearls. In the first approach, a polycondensation reaction of PEO macromonomers with partly protected dipentaerythritol leads first to a multiblock PEO. Afterward, the protected hydroxy groups of dipentaerythritol, which is situated at the junction points of the blocks, can be released for the anchoring of PDMAEMA chains. In the second approach, anionic polymerization of ethylene oxide leads directly to a diblock PEO with an interior dipentaerythritol unit. The chain ends can be modified with further dipentaerythritols, giving access after selective deprotection to either star dimers...

We present a systematic investigation of the crystallization and aggregation behavior of a poly(1,2-butadiene)-block-poly(ethylene oxide) diblock copolymer (PB-b-PEO) in n-heptane. n-Heptane is a poor solvent for PEO and at 70°C the block copolymer self-assembles into spherical micelles composed of a liquid PEO core and a soluble PB corona. Time- and temperature-dependent light scattering experiments revealed that when crystallization of the PEO cores is induced by cooling, the crystal morphology depends on the crystallization temperature (Tc): Below 30°C, the high nucleation rate of the PEO core dictates the growth of the crystals by a fast aggregation of the micelles into meander-like (branched) structures due to a depletion of the micelles at the growth front. Above 30°C the nucleation rate is diminished and a relatively small crystal growth rate leads to the formation of twisted lamellae as imaged by scanning force microscopy. All data demonstrate that the formation mechanism of the crystals through micellar aggregation is dictated by two competitive effects, namely, by the nucleation and growth of the PEO core.

We report on softening strategies for thermo-reversible organoferrogels obtained by physical gelation of ferrofluids with gelators of the SEBS type (polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene triblock copolymers). The first approach investigates a mixture of tri- and diblock copolymers, where the diblock copolymer could act as a plasticizer. The second approach tests triblock copolymers with a longer middle block, in this case the concentration and size of the crosslinking PS micellar cores should be smaller. Rheological, mechanical, magnetic, and morphological properties of these systems were studied and compared with the first generation of physical organoferrogels. Notably with both approaches we achieved a decrease of the softening temperature. Such soft magnetic organogels are important for upcoming actuators due to their easy deformation in magnetic fields.

Well-defined core−shell bishydrophilic cylindrical polymer brushes (CPBs) with a poly(2-hydroxyethyl methacrylate) (PHEMA) core and a poly(oligo(ethylene glycol) methacrylate) (POEGMA) shell were synthesized via the combination of anionic polymerization and atom transfer radical polymerization. They were used as a unimolecular cylindrical template for the controlled fabrication of linear assemblies of titania nanoparticles. The titania precursors were found localized mainly in the brush core via a transalcoholysis reaction and partially in the shell via a weak complexation force. After hydrolysis, the obtained titania−CPB hybrid nanowires are amorphous and soluble in organic solvents as well as water. A phase transition from amorphous titania to anatase titania was found by refluxing the hybrid nanowire solution for 5 days in a mixture of water/dioxane (vol. ratio = 1/3). They could also serve as in situ template for the pyrolytic formation of inorganic crystalline titania nanowires at 550 °C.

Dynamic core-shell-shell-corona micelles are formed between two oppositely charged block copolymer systems. Preformed polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB-P2VPq-PMAA) block terpolymer micelles with a soft polybutadiene core, an interpolyelectrolyte complex (IPEC) shell made out of poly(N-methyl-2-vinylpyridinium) and poly(methacrylic acid), and a negatively charged PMAA corona were mixed in different ratios at high pH with positively charged poly(N-methyl-2-vinylpyridinium)-block-poly(ethylene oxide) (P2VPq-PEO) diblock copolymers. Under these conditions, mixing results in the formation of a second IPEC shell onto the PB-P2VPq-PMAA precursor micelles, surrounded by a PEO corona. The resulting multicompartmented IPECs exhibit dynamic behavior, highlighted by a structural relaxation within a period of 10 days, investigated by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and scanning force microscopy (SFM). After a short mixing time of 1 h, the IPECs exhibit a star-shaped structure, whereas after 10 days, spherical core-shell-shell-corona objects could be observed. To further increase complexity and versatility of the presented systems, the in situ formation of gold nanoparticles (Au NPs) in both the precursor micelles and the equilibrated IPEC was tested. For the PB-P2VPq-PMAA micelles, NP formation resulted in narrowly distributed Au NPs located within the PMAA shell, whereas for the core-shell-shell-corona IPEC, the Au NPs were confined within the IPEC shell and shielded from the outside through the PEO corona.

The synthesis of several diblock copolymers with DMAEMA via anionic polymerization is presented; PS-b-PDMAEMA, PB-b-PDMAEMA, poly(p-tert-butoxystyrene)-b-PDMAEMA, and PEO-b-PDMAEMA. The latter was synthesized using sec-butyllithium as initiator in presence of the phosphazene base t-BuP 4 , enabling a facile changeover from an oxyanion to a carbanion. All reactions resulted in narrowly distributed block copolymers (PDI < 1.1). For PEO-b-PDMAEMA, diblock copolymers with a high blocking efficiency and a near-narrow molecular weight distribution (PDI < 1.40) could be prepared. The advantage of the presented one-pot synthesis is a significant higher blocking efficiency compared to commercially available PEO macroinitiators under similar conditions.

We studied the morphology of micelles formed by a well-defined poly(1,2-butadiene)-block-poly(ethylene oxide) diblock copolymer (PB-b-PEO). Dissolved in n-heptane at 70 °C, that is, above the melting point of PEO, spherical micelles are formed due to the selectivity of the solvent for the PB-block. If the solutions are cooled down to low temperatures, the liquid PEO-block crystallizes within the cores of the spherical micelles that remain stable. If, however, the solutions are quenched to 30 °C, the spherical micelles aggregate to a novel meander-like structure within several minutes. In its final state, the meander-like super-structure is crystalline, as revealed by time-resolved wide-angle X-ray scattering. The super-structure is shown to result from crystallization-induced aggregation of spherical micelles. Moreover, crystallization leads to well-defined angles between subsequent aggregating units. A quantitative Avrami-type analysis of the crystallization kinetics demonstrates that the formation of the meander-type structure resembles a 2D growth process combined with a breakout crystallization, showing an Avrami-exponent of 2.5. In contrast to this, crystallization at low temperatures resembles a confined crystallization with a low Avrami-exponent of 0.7. All data demonstrate that the morphology of block copolymers having a crystallizable block can be switched by the competition of aggregation and crystallization.

Immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) were batch-foamed using CO2 as a blowing agent as a function of foaming temperature, foaming time, and blend composition. Evaluation of the resulting cellular morphology revealed an enhanced foamability of SAN with PPE contents up to 20 wt% as indicated by a similar volume expansion but a significantly reduced mean cell size. This behavior is related to a heterogeneous nucleation activity by the dispersed PPE phase. A further increasing PPE content, however, leads to increasing foam densities as well as nonuniform foam morphologies. The changes in the foaming behavior can be correlated with the melt rheological properties and the corresponding blend morphology. Shear-rheological investigations revealed an onset of percolation of the dispersed PPE phase between 20 and 40 wt%, and a transition towards cocontinuity at 60 wt%. The materials response under uniaxial elongational flow, as assessed by Rheotens measurements, revealed an increase in elongational viscosity scaling with the PPE content, similar to the shear data. However, the strain hardening behavior was reduced by increasing PPE contents and, at 20 wt%, the drawability revealed a significant drop-both phenomena limiting the foamability of polymers. In summary, the present study discusses fundamental aspects of foaming immiscible PPE/SAN blends. POLYM. ENG. SCI., 48:2111–2125, 2008. © 2008 Society of Plastics Engineers

Precise control over the geometry of nanoscale one-dimensional structures is challenging. Cylindrical polymer brushes have now been used to synthesize organo-silica hybrid nanowires that are not only soluble in water but also in many organic solvents. There has been growing interest in the past decade in one-dimensional (1D) nanostructures, such as nanowires, nanotubes or nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices1,2. Significant progress has been made; however, the strict control of the distinctive geometry at extremely small size for 1D structures remains a great challenge in this field. The anisotropic nature of cylindrical polymer brushes has been applied to template 1D nanostructured materials, such as metal, semiconductor or magnetic nanowires3,4,5,6. Here, by constructing the cylindrical polymer brushes themselves with a precursor-containing monomer, we successfully synthesized hybrid nanowires with a silsesquioxane core and a shell made up from oligo(ethylene glycol) methacrylate units, which are soluble in water and many organic solvents. The length and diameter of these rigid wires are tunable by the degrees of polymerization of both the backbone and the side chain. They show lyotropic liquid-crystalline behaviour and can be pyrolysed to silica nanowires. This approach provides a route to the controlled fabrication of inorganic or hybrid silica nanostructures by living polymerization techniques.

We describe detailed investigations on the self-assembly of polybutadiene-block-poly(2-vinylpyridine) diblock copolymers into so-called crew-cut micellar aggregates in aqueous media. Three analogous diblock copolymers with different short segments of poly(2-vinylpyridine) were synthesized via anionic polymerization. The self-assembled aggregates are studied in dioxane/water mixtures by means of dynamic light scattering and transmission electron microscopy. Depending on the added volume fraction of water, spherical micelles, branched cylindrical micelles, and vesicles can be found. These aggregates can be cross-linked in a facile fashion using a UV photoinitiator. The structures of the crew-cut aggregates remain intact during cross-linking, yielding stabilized polymeric nanoparticles. A transfer of these nanoparticles into common, only slightly selective solvents, in which no aggregates or different type of aggregates would exist without cross-linking, is possible. The cross-linked nanoparticle structures remain unchanged during this process. Moreover, a new pathway for the phase transition of cylindrical micelles to vesicles was found and is elucidated.

The thermo-reversible formation of wormlike micelles from a polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA) triblock terpolymer with a crystallizable middle block in organic media is presented. The formation of wormlike micelles is rather unexpected, because PE containing diblock copolymers usually form platelet-like structures. Transmission electron microscopy (TEM) investigations revealed a core−corona structure for the wormlike micelles. The core is formed by crystalline PE domains, and the soluble corona exhibits a patched structure composed of microphase-separated PS and PMMA chains. Microphase separation of the coronal chains was proven by 2D 1H nuclear Overhauser effect spectroscopy (NOESY) and TEM investigations of selectively stained samples. A combination of various techniques, such as differential scanning calorimetry (DSC), dynamic light scattering (DLS), and scanning force microscopy (SFM), indicated that the wormlike micelles might be formed by crystallization...

The isothermal crystallization kinetics of PEO and PE blocks within various triblock terpolymers were studied by DSC. The effect of the geometry of the microdomains was analyzed by studying different compositions of PE-b-PS-b-PEO triblock terpolymers. The crystallization rate decreased for decreasing block content for both crystallizable blocks. The effect of the microdomain geometry, confinement or chain tethering on the crystallization of PEO was extensively studied by comparing pairs of triblock terpolymers with differences either in the nature (crystalline, glassy, amorphous) or in the location of the other blocks in the terpolymer.

The confined crystallization of poly(ethylene oxide) (PEO) in predominantly spherical microdomains formed by several diblock copolymers was studied and compared. Two polybutadiene-b-poly(ethylene oxide) diblock copolymers were prepared by sequential anionic polymerization (with approximately 90 and 80 wt % polybutadiene (PB)). These were compared to equivalent samples after catalytic hydrogenation that produced double crystalline polyethylene-b-poly(ethylene oxide) diblock copolymers. Both systems are segregated into microdomains as indicated by small-angle X-ray scattering (SAXS) experiments performed in the melt and at lower temperatures. However, the PB-b-PEO systems exhibited a higher degree of order in the melt. A predominantly spherical morphology of PEO in a PB or a PE matrix was observed by both SAXS and transmission electron microscopy, although a possibly mixed morphology (spheres and cylinders) was formed when the PEO composition was close to the cylinder-sphere domain transitional composition as indicated by SAXS. Differential scanning calorimetry experiments showed that a fractionated crystallization process for the PEO occurred in all samples, indicating that the PE cannot nucleate PEO in these diblock copolymers. A novel result was the observation of a subsequent fractionated melting that reflected the crystallization process. Sequential isothermal crystallization experiments allowed us to thermally separate at least three different crystallization and melting peaks for the PEO microdomains. The lowest melting point fraction was the most important in terms of quantity and corresponded to the crystallization of isolated PEO spheres (or cylinders) that were either superficially or homogeneously nucleated. This was confirmed by Avrami index values of approximately 1. The isothermal crystallization results indicate that the PE matrix restricts the crystallization of the covalently bonded PEO to a higher degree compared to PB.

The mechanical performance of immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) and the subsequent influence of compatibilisation by tailored polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock terpolymers (SBM) on the mechanical performance under static and dynamic loads is analysed in detail. A PPE/SAN 60/40 blend was selected as a base system for the compatibilisation experiments. The observed static tensile behaviour is described by micromechanical models and correlated to the blend microstructures as observed by transmission electron microscopy. In most cases, the addition of the SBM triblock terpolymers further enhances the ductility of the blend while only leading to a minor reduction of modulus and strength. Triblock terpolymers with symmetric end blocks, mainly located at the interface between PPE and SAN, led to nearly isotropic specimens. In contrast, SBM materials with a longer polystyrene block predominantly formed micelles in the PPE phase and the blends revealed a highly anisotropic morphology. Comparative investigations of the fatigue crack growth behaviour parallel to the direction of injection also reflected this variation in mechanical anisotropy of the compatibilised blends. A poor toughness and a predominant interfacial failure were observed in the case of the SBM with a long polystyrene block. In contrast, a considerable improvement in properties as a result of pronounced plastic deformations was observed for blends compatibilised by triblock terpolymers with symmetric end blocks. The systematic correlation between morphology and mechanical performance of compatibilised PPE/SAN blends established in this study provides an efficient way for the desired selection of suitable and effective compatibilising agents, ensuring both a superior multiaxial toughness as well as a high strength and modulus of the overall system.

A template synthesis allows the preparation of monodisperse nanoparticles with high reproducibility and independent from self-assembly requirements. Tailor-made polymer cages were used for the preparation of nanoparticles, which were made of cross-linked macromolecules with pendant thiol groups. Gold nanoparticles (AuNPs) were prepared in the polymer cages in situ, by using different amounts of cages versus gold. The polymer cages exhibited a certain capacity, below which the AuNPs could be grown with excellent control over the size and shape. Control experiments with a linear diblock copolymer showed a continuous increase in the AuNP size as the gold feed increased. This completely different behavior regarding the AuNP size evolution was attributed to the flexibility of the polymer chain depending on cross-linking. Moreover, the polymer cages were suitable for the encapsulation of AgNPs, PdNPs, and PtNPs by the in situ method.

A first attempt was made to produce novel ABC triblock terpolymers with three potentially crystallisable blocks: polyethylene (PE), poly(ethylene oxide) (PEO), and poly(e-caprolactone) (PCL). Polybutadiene-b-poly(ethylene oxide) diblock copolymers were synthesized by living anionic polymerization. Then, a non-catalyzed thermal polymerization of e-caprolactone from the hydroxyl end group of the PB-b-PEO diblock precursors was performed. Finally, hydrogenation by Wilkinson catalyst produced PE-b-PEO-b-PCL triblock terpolymers. Side reactions were detected that lead to the formation of undesired PCL-b-PEO diblock copolymers, however, these impurities were successfully removed by purification. A range of triblock terpolymers with PCL and PEO minor components were prepared. Topological restrictions on the PEO middle block prevented this block from crystallizing while the complex crystallization behavior of the PE and PCL blocks was documented by DSC and WAXS measurements.

We present a convenient method to synthesize polymers with primary amino groups by end-capping of living anionic chain ends with nitriles followed by reduction in a one-pot process. As an example, the addition of pivalonitrile to the chain ends of oligobutadienyllithium in toluene, followed by the reduction with sodium borohydride quantitatively leads to ω-amino-oligo-1,4-butadiene, as demonstrated by 1 H and 13 C NMR, thin-layer chromatography and MALDI-ToF mass spectrometry.

Immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) with a weight composition of 60/40 were compatibilised by polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock terpolymers (SBM) using a two-stage melt-processing approach. In order to investigate the influence of the SBM composition on the compatibilisation efficiency, the block lengths of the triblock terpolymers were systematically varied. The resulting morphological features of the blend systems as function of SBM composition and processing parameters are correlated with the resulting thermal and thermo-mechanical properties. In the ideal case, SBM should be located at the interface as PS is miscible with PPE while PMMA is miscible with SAN. The elastomeric middle block as an immiscible component should remain at the interface. This particular morphological arrangement is known as the ‘raspberry morphology’. A detailed TEM analysis of the blend morphologies following initial extrusion-compounding revealed a high compatibilisation efficiency of the SBM types with equal lengths of the end blocks and, furthermore, the desired raspberry morphology was achieved. In contrast, high PS contents in comparison to the other blocks led to a pronounced micelle formation in the PPE phase. Further evaluation of the blend structures following injection-moulding indicated that the morphologies remain relatively stable during this second melt-processing step. A detailed thermal analysis of all blend systems supports the interpretation of the observed morphological features. The fundamental correlation between SBM composition and blend morphology established in this study opens the door for the controlled development of interfacial properties of such compatibilised PPE/SAN blends during melt-processing.

We discuss the use of fluorescence correlation spectroscopy (FCS) to study the diffusion of single dye-labeled polymer chains in organic solvents. Monodisperse batches of polystyrenes labeled with a single Rhodamine B molecule have been synthesized via anionic polymerization of styrene and ethylene oxide end-capping followed by a polymer analogous coupling reaction. MALDI-ToF mass spectrometry is used to characterize the resulting material. A commercial FCS system has been modified to permit FCS measurements in volatile organic solvents. FCS was used to determine the molecular weight dependence of the diffusion coefficient of 10 nM solutions of end-labeled polystyrenes in toluene. The data are utilized to establish a calibration procedure for FCS measurements in organic solvents.

Thermoplastic elastomers are used in a wide range of applications due to easy processing by conventional methods like injection molding and extrusion. ABC triblock copolymers with two hard domain forming end blocks in a rubbery matrix of B are one way to approach thermoplastic elastomers. In this contribution we will compare polystyrene-block-poly(ethylene-alt-propylene)-block-polyethylene (PS-b-PEP-b-PE) and polystyrene-block-poly-(ethylene-alt-propylene)-block-polystyrene (PS-b-PEP-b-PS) triblock copolymers with similar middle block content with respect to their morphological and mechanical properties. Transmission electron microscopy (TEM) and scanning force microscopy (SFM) reveal for the PS-b-PEP-b-PE triblock copolymers a morphology consisting of PS cylinders and PE crystallites within a matrix of the PEP block. Mechanical characterization of these triblock copolymers demonstrated that for small strains the PS-b-PEP-b-PE triblock copolymers exhibit the aimed smaller plastic deformations, i.e. better elastic properties, compared to the polystyrene based ABA type thermoplastic elastomers. However, at high strains the PS-b-PEP-b-PS triblock copolymers show a significantly better elastic recovery.

Fourier-transform near-infrared (FT-NIR) fiber-optic spectroscopy was successfully used to monitor the anionic polymerization of ethylene oxide (EO). Kinetic data are provided for the polymerization of EO with the sec-BuLi/Bu t P 4 initiating system under different initiators and reaction conditions on the polymerization of EO is investigated. Online monitoring using NIR spectroscopy revals an unexpected induction period present in EO homopolymerizations as well as in the synthesis of PEO containing block copolymers with [Li/Bu t P 4 ] + counterions. The resulting polymers are characterized by size exclusion chromatography (SEC). A low-molecular-weight polystyrene-block-poly(ethyelen oxide) (PS-b-PEO) diblock copolymer was synthesized to gain more insight into the observed induction period by matrix-assisted laser desorption ionization time-of-flight mass spectrometrhy (MALDI-ToF MS) on samples taken during EO polymerization. The induction period is believed to be a result of different factors involved in the formation of active centers, for example, the break up of lithium alkoxide aggregates by the phosphazene base Bu t P 4 , and chain lenght effects. It depends on reaction temperature, concentration of the phosphazene base Bu t P 4 , as well as the structure of the initiator.

The influence of different confinements active during crystallization within polybutadiene-block-polyisoprene-block-poly(ethylene oxide) (PB-b-PI-b-PEO) and the corresponding hydrogenated polyethylene-block-poly(ethylene-alt-propylene)-block-poly(ethylene oxide) (PE-b-PEP-b-PEO) triblock copolymers on the self-nucleation behavior of the crystallizable PEO and PE blocks is investigated by means of differential scanning calorimetry (DSC). In triblock copolymers with PEO contents ≤ 20 wt.-% crystallizationof PEO is confined within small isolated microdomains (spheres or cylinders), and PEO crystallization takes place exclusively at high supercoolings. Self-nucleation experiments reveal an anomalous behavior in comparison to the classical self-nucleation behavior found in semicrystalline homopolymers. In these systems, domain II (exclusive self-nucleation domain) vanishes, and self-nucleation can only take place at lower temperatures in domain III SA , when annealing is already active. The self-nucleation behavior of the PE blocks is significantly different compared with that of the PEO blocks. Regardless of the low PE content (10-25 wt.-%) on the investigated PE-b-PEP-b-PEO triblock copolymers a classical self-nucleation behavior is observed, i.e., all three self-nucleation domains, usually present in crystallizable homopolymers, can be located. This is a direct result of the small segmental interaction parameter of the PEP and PE segments in the mel. As a consequence, crystallization of PE occurs without confinement from a homogeneous mixture of PE and PEP segments. Self-nucleation regimes of a block copolymer showing confined crystallization by means of DSC.

The preparation of polyethylene-block-poly(ethylene-alt-propylene)-block-poly(ethylene oxide) (PE-b-PEP-b-PEO) triblock copolymers by homogeneous catalytic hydrogenation of the precursor poly(1,4-butadiene)-block-poly(1,4-isoprene)-block-poly(ethylene oxide) (PB-b-PI-b-PEO) triblock copolymers, which were synthesized by sequential anionic polymerization, is described. Thermal analysis using differential scanning calorimetry (DSC) reveals differences in the crystallization behavior of the PEO and PE blocks arising from different morphological confinements active during crystallization. If the PEO block is confined into isolated spherical or cylindrical microdomains, crystallization can only be induced by high supercoolings resulting from the vast number of microdomains (spheres or cylinders) compared to the number of available heterogeneities. In contrast, crystallization of PE proceeds via heterogeneous nucleation regardless of the composition, which can be attributed to the miscibility of PEP and PE segm...

The morphology of copoly(ether ester) elastomers, based on poly(butylene terephthalate) (PBT) hard blocks and poly(ethylene oxide)-block-poly(ethylene-stat-butylene)-block-poly(ethylene oxide) (PEO-b-PEB-b-PEO) soft blocks, has been investigated by various solid-state NMR methods. 13C IRCP and 1H T1ρ NMR experiments show a heterogeneity in molecular motions for the PEO and PBT segments, indicating the presence of a PEO-rich phase and a PEO/PBT mixed phase. In contrast, for the PEB segments a homogeneous NMR relaxation behavior is observed, indicating the presence of a separate pure PEB phase. Deuterium NMR spectra recorded of block copolymers with selectively deuterated PBT clearly show at least two distinct motional environments of PBT already at room temperature: a broad peak which is assigned to PBT segments in a crystalline phase and an extremely narrow peak which is assigned to highly mobile PBT segments embedded in an amorphous matrix (PBT/PEO mixed phase). For copoly(ether ester)s with a relativel...

We have been able to prepare a molecular complex between the poly(ethylene oxide) block of a poly(ethylene)-b-poly(ethylene-alt-propylene)-b-poly(ethylene oxide) triblock copolymer and p-nitrophenol (PNP). The composition of the copolymer employed was: 24% PE, 57% PEP and 19% PEO in weight percent. The pure copolymer exhibited a nonconventional thermal behavior since the PEO block displayed a fractionated crystallization process during cooling. The PEO block /PNP complex did not show any apparent crystallization during cooling, instead cold crystallization during heating was observed and an approximately 30 °C increase in melting point as compared to the neat PEO block within the copolymer. This caused an overlap in the melting regions of the PE block and the PEO block/PNP complex. The self-nucleation of the PE-b-PEP-b-PEO/PNP complex is very different from that of the neat triblock copolymer. An increased capacity for self-nucleation of the PEO block was produced by the complexation with PNP and therefore the three self-nucleation domains were clearly encountered for both the PE block and for the PEO block/PNP complex. Self-nucleation was able to show that the two crystallizable blocks can be self-nucleated and annealed in an independent way, thereby ascertaining the presence of separate crystalline regions in the triblock copolymer. Through the use of PNP, both the crystallinity and the melting point of the PE-b-PEP-b-PEO block copolymer employed here can be substantially increased. Similar results were obtained by complexation of the same ABC triblock copolymer with resorcinol.

The elasticity of commonly known poly(butylene terephthalate)−poly(tetramethylene oxide) (PBT−PTMO)-based copoly(ether ester)s is increased by replacement of PTMO soft segments with poly(ethylene oxide)-block-poly(ethylene-stat-butylene)-block-poly(ethylene oxide) (PEO-b-PEB-b-PEO) triblock copolymer soft segments containing a nonpolar middle block based on hydrogenated polybutadiene (PEB). The incorporation of this strongly incompatible PEB block resulted in the aimed increased phase separation between the PBT hard blocks and the soft segment phase, leading to a disperse PBT phase and hence to an increased elasticity. Dynamic shear experiments in combination with small-angle X-ray scattering revealed that crystallization of the PBT hard segments occurs from a microphase-separated melt. The resulting dispersed PBT hard phase in these materials is shown using transmission electron microscopy (TEM) and scanning force microscopy (SFM), whereas the increased elasticity is demonstrated using mechanical charact...