Search

Based on the highly disparate reactivities of isoprene (I

The development of diblock copolymer (DBC) nanocomposite films containing magnetic nanoparticles (NPs) with diameters (D) over 20 nm is a challenging task. To host large iron oxide NPs (Fe3O4, D = 27 ± 0.6 nm), an ultrahigh molecular weight (UHMW) linear DBC polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is used as a template in the present work. Due to hydrogen bonding between the carboxylic acid ligands of the NPs and the ester groups in PMMA, the NPs show an affinity to the PMMA block. The localization of the NPs inside the DBC is investigated as a function of the NP concentration. At low NP concentrations, NPs are located preferentially at the interface between PS and PMMA domains to minimize the interfacial tension caused by the strong segregation strength of the UHMW DBC. At high NP concentrations (≥10 wt %), chain-like NP aggregates (a head-to-tail orientation) are observed in the PMMA domains, resulting in a change of the morphology from sphere to ellipsoid for part of the PMMA domains. Magnetic properties of the hybrid films are probed via superconducting quantum interference device magnetometry. All hybrid films show ferrimagnetism and are promising for potential applications in magnetic data storage.

The synthesis of tapered multiblock copolymers by statistical living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in cyclohexane is based on vastly different reac...

Anion-adsorbing membranes provide an interesting possibility to remove toxic arsenate and chromate from drinking water. A promising way to prepare anion-exchange materials is to introduce positively charged amine groups on polymers. In this study, polyacrylonitrile (PAN) ultrafiltration membranes were modified with amine functionalities on the mem-branes. The success of the modifications was demonstrated using infrared spectroscopy and zeta potential measurements. Additionally, the arsenate adsorption was analyzed. The modified membrane showed arsenate adsorption 5 times higher than the pristine PAN membrane.

Ultrahigh molecular weight (UHMW) block copolymers (BCPs) are promising candidates for the fabrication of photonic materials. Here, we demonstrate the synthesis and self-assembly capability of well...

To explore the potential of myrcene (Myr) as a bio-based monoterpene comonomer for styrenic copolymers and to establish its general applicability for the carbanionic copolymerisation, several statistical copolymerisations of myrcene and common monomers like isoprene (I), styrene (S) and 4-methylstyrene (4MS) were carried out in cyclohexane and monitored by in situ1H NMR spectroscopy. Real-time NMR kinetic studies permitted the determination of the reactivity ratios and the composition profile for each monomer combination. While the copolymerisation of Myr/I yielded a gradient copolymer and reactivity ratios of moderate disparity (rMyr = 4.4; rI = 0.23), the statistical copolymerisation of Myr/S and Myr/4MS afforded block-like, tapered copolymers due to highly diverging reactivity ratios (rMyr = 36; rS = 0.028 and rMyr = 140; r4MS = 0.0074). Furthermore, a terpolymerisation of Myr/I/4MS was studied by real-time NMR kinetics, revealing an alteration of the composition profile of 4MS towards a more block-like structure. Based on the kinetic studies, a series of Myr/I/4MS terpolymers and Myr/S copolymers was prepared by statistical living anionic copolymerisation. All copolymers showed narrow molecular weight distributions (SEC) and two glass transition temperatures (Tg,1 = −51 to −62 °C; Tg,2 = 93 to 107 °C), suggesting phase segregation. TEM and SAXS measurements revealed highly ordered lamellar morphologies for all copolymers with long range correlation and confirmed the block-like structure and behaviour of Myr/S and Myr/4MS copolymers prepared by statistical carbanionic copolymerisation.

The living anionic copolymerization of isoprene and styrene in cyclohexane affords tapered block copolymers due to the highly disparate reactivity ratios of rI = 12.8 and rS = 0.051. Repeated addit...

Based on the highly disparate reactivities of isoprene (I, rI = 25.4) and 4-methylstyrene (4MS, r4MS = 0.007) in the anionic copolymerization in nonpolar media, a general strategy for the rapid and scalable synthesis of tapered multiblock copolymers with an extremely steep gradient has been developed. A repetitive addition strategy of a mixture of isoprene and 4MS leads to a tapered diblock in each case, giving access to linear alternating multiblock copolymers of the (AB)n type with up to 10 blocks. All multiblock copolymers showed narrow molecular weight distributions (dispersity Đ = 1.04–1.12). High molecular weights in the range of 80 to 400 kg mol–1 were achieved. Due to the incompatibility of PI and P4MS segments, the multiblock copolymers exhibit nanophase separation, manifested by separate glass transitions for both constituents. Stress–strain measurements revealed extraordinary toughness and elongations up to 1150% strain at break, even at a 50/50 molar ratio I/4MS (i.e., 37 wt% isoprene). Our sy...

Block copolymers of polyisoprene and polystyrene are key materials for polymer nanostructures as well as for several commercially established thermoplastic elastomers. In a combined experimental and kinetic Monte Carlo simulation study, the direct (i.e., statistical) living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in nonpolar media was investigated on a fundamental level. In situ 1H NMR spectroscopy enabled to directly monitor gradient formation during the copolymerization and to determine the nature of the gradient. In addition, a precise comparison with the established copolymerization of isoprene and styrene (I/S) was possible. Statistical copolymerization in both systems leads to tapered block copolymers due to an extremely slow crossover from isoprene to the styrenic monomer. For the system I/4MS the determination of the reactivity ratios shows highly disparate values with rI = 25.4 and r4MS = 0.007, resulting in a steep gradient of the comonomer composition. Th...

The molecular design of smart polymer surfaces and control over functionality in a way that the properties can be changed by external triggers garnered a great deal of attention of polymer chemists in the last decade. Here, we introduce the formation of a dual-responsive, i.e. reduction- and oxidation-responsive, cobalt-containing polymer core-shell particle system, displaying a reversibly switchable behavior by means of chemical oxidation reagents as well as electrochemistry experiments. The responsiveness is based on a cobalt(I)-containing shell material, which is obtained by a surface-initiated atom transfer radical polymerization (SI-ATRP) protocol for (η 5 -cyclopentadienyl-4-hydroxybutan-1-on)cobalt(η 4 -tetraphenyl-cyclobutadiene) methacrylate (CpCoCbMA). The novel metallopolymer particles featuring a cobalt-containing shell are investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), while control over the ATRP approach is shown by characterizing freely formed poly(CpCoCbMA) chains by size-exclusion chromatography (SEC). The responsive behavior of the poly(CpCoCbMA)-containing shell is investigated by dynamic light scattering (DLS) and cyclic voltammetry (CV) measurements indicating a tremendous change of the particle hydrodynamic radii and dispersion capability in organic polar and non-polar solvents. Transformation of these preceramic cobalt-grafted core-shell particles to cobalt oxide-based materials is investigated after convenient thermal treatment. Overall, the herein reported redox-mediated core-shell cobalt-containing polymer architectures open a variety of applications for switchable and electrochemical devices.

Ultrahigh molecular weight (UHMW) diblock copolymers (DBCs) have emerged as a promising template for fabricating large-sized nanostructures. Therefore, it is of high significance to systematically study the influence of film thickness and solvent vapor annealing (SVA) on the structure evolution of UHMW DBC thin films. In this work, spin coating of an asymmetric linear UHMW polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) DBC is used to fabricate thin films, which are spherically structured with an inter-domain distance larger than 150 nm. To enhance the polymer chain mobility and facilitate approaching equilibrium nanostructures, SVA is utilized as a post-treatment of the spin coated films. With increasing film thickness, a local hexagonal packing of PMMA half-spheres on the surface can be obtained, and the order is improved at larger thickness, as determined by grazing incidence small angle X-ray scattering (GISAXS). Additionally, the films with locally hexagonal packed half-spherical morphology show a poor order-order-poor order transition upon SVA, indicating the realization of ordered structure using suitable SVA parameters.

A variety of applications of amphiphilic block copolymers result from the control of their self-assembled structures. Herein, the synthesis and structure formation of block copolymers (BCPs) consisting of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) as one segment and poly(methyl methacrylate) (PMMA) or a statistical copolymer (PDMAEMA-co-PMMA) as a second segment, is described. The BCPs provide molar masses between 8.9 kg mol−1 and 35.6 kg mol−1 with low polydispersity index values, Đ = 1.05–1.13. BCPs are synthesized via sequential anionic polymerization strategies while structure formation in water is investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The PDMAEMA-containing micelles in water are loaded with a Ru(II) polypyridyl complex, i.e. [Ru(bipy)2-dppz-7-hydroxymethyl][PF6]2 (bipy = 2,2′-bipyridine; dppz = dipyridophenazine), which was previously shown to act as a potential photosensitizer in photodynamic therapy (PDT). Successful loading of the BCP micelles is evidenced by TEM measurements after dialysis in water. Stimulus-responsive release of the Ru(II) complex from the BCP micelles is shown using ultrasound, change of pH or temperature as external triggers. The quantification and release profiles for the Ru(II) complex are obtained by atomic absorption spectrometry (AAS). As a result, PDMAEMA-b-PMMA is not capable of releasing the Ru(II) complex in a controlled manner after application of, for instance, ultrasound or temperature change as external triggers due to the shielding (stealth effect) of the BCP. On the contrary, micelles made of BCPs featuring PDMAEMA and PDMAEMA-co-PMMA segments reveal excellent Ru(II) complex release profiles due to the tailored molecular composition of the underlying block segments as evidenced by temperature-dependent DLS and AAS measurements. Thus, these smart PDMAEMA-containing BCPs pave the way to a variety of applications for selective triggered release of small molecules.

Microphase separation drives the structure formation in block copolymers. Here, functional metallopolymer-grafted diblock copolymers consisting of polystyrene-block-polyisoprene (PS-b-PI) as polymer backbone featuring low molar mass polyferrocenyldimethylsilane (PFS) and polyvinylferrocene (PVFc) are synthesized via an iterative anionic grafting-to polymerization strategy. PS-b-PI block copolymers having about 30 mol % 1,2-polyisoprene moieties are subjected to platinum-catalyzed hydrosilylation reaction for the introduction of chlorosilane groups. The Si–Cl moieties are shown to efficiently react with the active metallopolymers yielding block-selective metallopolymer-grafted copolymers with 34 vol % PVFc and 43 vol % PFS as evidenced by 1H NMR spectroscopy as well as size exclusion chromatography. The microphase separation of the functional metallopolymer-grafted block copolymers is evidenced via TEM measurements revealing fascinating morphologies. The structure formation of the PVFc-grafted block copoly...

Ultrahigh-molecular-weight (UHMW) tapered block copolymers (BCPs) consisting of polyisoprene-block-poly(4-methylstyrene) featuring overall molar masses in the range of 1101–2033 kg mol–1 (Mw) are synthesized via a convenient one-step anionic copolymerization protocol. The obtained UHMW BCPs are investigated by differential scanning calorimetry, size exclusion chromatography, and 1H NMR spectroscopy. Microphase separation for the UHMW BCPs in the bulk state is investigated by transmission electron microscopy (TEM) measurements and scanning electron microscopy (SEM), revealing well-ordered lamellar and spherical domains with large domain sizes in the range of 100–200 nm. Excellent order and periodicity are observed for lamellar morphologies over large film areas of 90 × 120 μm. Because of this high order of the underlying domains and the different refractive indices of the block segments, vivid structural colors can be observed in the bulk state. Structural colors of BCP films are investigated by angle-depe...

Stimuli-responsive micro- to nano-scale containers have gained increasing attention due to their unique potential to selectively release payloads under specific environmental conditions. We report here novel triple stimuli-responsive nanocapsules that selectively respond to changes in temperature, pH value, and redox potential. The nanocapsules were prepared from either a triple responsive triblock terpolymer or a blend of responsive diblock copolymers, both synthesized by sequential anionic polymerization. We then compared the release performance of nanocapsules under oxidative conditions and changes of temperature or pH value. Our results reveal the close correlation between the release properties of stimuli-responsive nanocontainers and the microstructure of the polymer shell. In fact, the microphase separation between the responsive diblock copolymers across the shell significantly hinders the triggered release of the payload from the nanocapsules. These results demonstrate that the fine morphology of triblock terpolymers can be exploited to achieve the triggered release of payloads from polymer nanocontainers upon application of three different external triggers.