Search

This work reports a reversible braking system for micromotors that can be controlled by small temperature changes (≈5 °C). To achieve this, gated‐mesoporous organosilica microparticles are internally loaded with metal catalysts (to form the motor) and the exterior (partially) grafted with thermosensitive bottle‐brush polyphosphazenes to form Janus particles. When placed in an aqueous solution of H2O2 (the fuel), rapid forward propulsion of the motors ensues due to decomposition of the fuel. Conformational changes of the polymers at defined temperatures regulate the bubble formation rate and thus act as brakes with considerable deceleration/acceleration observed. As the components can be easily varied, this represents a versatile, modular platform for the exogenous velocity control of micromotors., A robust and easily tunable micromotor platform is reported, based on Janus gated‐mesoporous organosilica microparticles with reversible, external responsive braking systems using bottle‐brush polyphosphazenes to control acceleration/deceleration by small changes in temperature.

The ability to prepare block, multiblock and segmented polymers is an essential and established tool in polymer chemistry to tailor the properties of materials and steer the formation of complex nanostructures. The preparation of segmented or block copolymers with pre-defined block lengths is, however, inherently difficult for polyimides, one of the most important and versatile high-performance polymers. The most accessible route to polyimides, a step-growth polyamic acid formation between diamines and dianhydrides, is in dynamic equilibrium, which leads to chain scrambling of attempted block copolymers. We provide herein a solution to this by utilizing a Diels–Alder reaction on phenylethynyl end-functionalized oligomers containing pre-formed, ring-closed imides. The reaction of the alkynes with a bistetraphenylcyclopentadienone chain extender undergoes a chelotropic evolution of CO gas at high temperatures forming phenylene segments and polymerizing the chains in the process. Furthermore, we could use this reaction for the chain extension of different phenylethynyl functionalized telechelic oligoimides and thus produce random multiblock copolymers. Importantly the reaction is also demonstrated to enable chain extension reactions with insoluble oligoimides, considerably expanding the scope of potential as many important polyimides are either insoluble, or poorly soluble, in common organic solvents. This Diels–Alder polymerization is thus demonstrated to be a highly versatile route to prepare novel polyimides with wide-ranging possibilities and considerable potential to prepare advanced materials ranging from electronic applications to high-performance materials.

Despite the current advancements, yet improving the intrinsic structure and external environmental stability of hybrid metal halide perovskite nanomaterials is required for developing efficient perovskite-based devices. Up-to-date, a very attractive method is growing and/or embedding perovskite nanocrystals within organic polymeric matrices, or into porous inorganic and hybrid nano/micromaterials (e. g., metal-organic frameworks, mesoporous silica, zeolites, and others), favored through confinement effect within the pores. In this review, we highlighted the last two years of research progress on enhancing the stabilization of perovskite nanoparticles based on methylammonium cations. In the future generation of optoelectronic and photovoltaic devices along with other interesting applied fields, it is predicted that an effective way to trigger the widespread use of this type of perovskite nanocrystals may involve combining different functional host materials, acting as a smarter protection method for the guest nanocrystals.

An approach to reduce cycle times in injection molding of poly (lactic acid) through the use of bio-based nucleating agents is presented. Talc is commonly used as nucleant and will be used as the reference in this study. The other investigated additives are kraft lignin, lignosulfonate, and carbon black. This is an in-depth study of certain bio-based nucleating agents for use with poly (lactic acid) under various processing conditions. Bio-based compounds of poly (lactic acid) and different nucleating agents were produced via twin-screw extrusion. Subsequent injection molding yielded standard samples for tensile testing; cycle times were recorded during injection molding. Thermal and mechanical testing showed direct dependence upon the degree of crystallinity in the matrix polymer. The ability of certain bio-based nucleating agents (e.g. kraft lignin) to reduce the cycle time in injection molding was proven.

Thermoplastic materials used in coatings, paints and adhesives as well as structural applications for sensitive substrates, such as wood, paper or polymers, often lack the required chemical and environmental resistance for many applications, which can be overcome by covalent cross-linking. Covalent cross-linking improves chemical and mechanical properties of the material and has been used for many different materials and applications. Room temperature cross-linking can be initiated by different mechanisms and eliminates energy intensive heating as well as conditions potentially harmful for the substrate. The present article focuses on cross-linking strategies applied for different materials, such as thermoplastics and thermosets. It is organized by material class, followed by an overview about triggering mechanisms for cross-linking reactions at room temperature. The authors hope to provide helpful insights about the methods for covalent cross-linking already published.

In this paper we present the preparation and application of a novel soluble phosphine functionalized polyphosphazene (poly[3-(diphenylphosphino)propylamino]phosphazene) and investigate its application as a polymeric reagent. Upon chlorination of the pendant phosphine groups, the polymer was found to facilitate the rapid and efficient transformation of alcohols to the corresponding chlorides and bromides under Appel-type conditions. Reaction times followed by 31P NMR spectroscopy are shown to be rapid (several minutes) and the yields for the transformation of alcohols to the corresponding halides are in the range 80–99 %. The facile recovery of the oxidized polymeric agent by precipitation is also described, offering a significant advantage over notoriously difficult to remove small molecule phosphine oxide by-products. Furthermore the regeneration of the reactive phosphine chloride pendant groups is demonstrated, which could be efficiently re-used in a further chlorination reaction.

Photo-polymerizable scaffolds are designed and prepared via short chain poly(organo)phosphazene building blocks bearing glycine allylester moieties. The polyphosphazene was combined with a trifunctional thiol and divinylester in various ratios, followed by thiol-ene photo-polymerization to obtain porous matrices. Degradation studies under aqueous conditions showed increasing rates in correlation with the polyphosphazene content. Preliminary cell studies show the non-cytotoxic nature of the polymers and their degradation products, as well as the cell adhesion and proliferation of adipose-derived stem cells.

Microcapsules are synthesized via the self-assembly of silk-fibroin microspheres with polycaprolactone in a colliodosome preparation procedure. The microsphere building blocks with controlled diameter are prepared from the naturally occurring biopolymer, silk fibroin, and then act as stabilizers for oil-in-water (O/W) emulsion and organized themselves on the surface of chloroform droplets to form the capsules. The concentration of the protein-based microspheres and the binding polycacrolactone is used to tailor the size, as well as the permeability of the resultant capsules. Furthermore, microencapsulation of fluorescently labeled macromolecules (20-2000 KDa) is demonstrated. The permeability of the capsules is observed to be stimuli responsive, making it possible to incorporate a pH-triggered payload release from the capsules. The relatively simple preparation of capsules with controlled dimensions and tunable permeability, alongside the biocompatibility and biodegradability of both polymer components makes these promising materials for potential use in smart drug-delivery systems.

This feature article briefly highlights some of the recent advances in polymers in which phosphorus is an integral part of the backbone, with a focus on the preparation of functional, highly branched, soluble polymers. A comparison is made between the related families of materials polyphosphazenes, phosphazene/phosphorus-based dendrimers and polyphosphoesters. The work described herein shows this to be a rich and burgeoning field, rapidly catching up with organic chemistry in terms of the macromolecular synthetic control and variety of available macromolecular architectures, whilst offering unique property combinations not available with carbon backbones, such as tunable degradation rates, high multi-valency and facile post-polymerization functionalization. As an example of their use in advanced applications, we highlight some investigations into their use as water-soluble drug carriers, whereby in particular the degradability in combination with multivalent nature has made them useful materials, as underlined by some of the recent studies in this area.

Five different maleic anhydride grafted polypropylene (PP) coupling agents (CAs) have been tested in wood polymer composites with wood contents of 40% and 60%. The tested CAs cover a wide range of backbone molecular weight ( Mw 55–181 kDa) and also vary in MA graft level (0.5–1.5%). Furthermore, one PP copolymer-based product is among them. Mechanical properties (flexural strength, impact strength and heat deflection temperature) and water absorption (WA) have been evaluated as responses. Finally, dynamic rheological measurements on several compounds have been performed. The results show that the backbone polymer structure of the CA is the most important factor for its efficiency. Molecular weight seems to have an influence on WA properties. As regards to rheological measurements, a lubricant-like effect of a CA indicates a reduced capability for compatibilization at the interface.

Using a living cationic polymerisation procedure we synthesised a series of multi-armed poly(organo)phosphazenes with controlled molecular weights and excellent aqueous solubility. The synthetic flexibility of polyphosphazenes was exploited in order to incorporate an acid-sensitive hydrazide linker to the polymer backbone, as well as tumour-targeting folic acid groups. We were then able to attach hydrophobic anti-cancer drug molecules via the pH labile linker and studied its pH-triggered release kinetics from the polymeric carrier. Although stable for short periods (several days) in an aqueous environment, the polymers were shown to degrade over longer periods (weeks) under simulated physiological conditions. Furthermore, the rate of degradation could be tailored through careful selection of substituents. These biodegradable, multi-functional polyphosphazenes represent promising candidates for use as macromolecular carriers for the tumour-targeted delivery of anti-cancer drugs.

Porous polymer monoliths are considered to be one of the major breakthroughs in separation science. These materials are well known to be best suited for the separation of large molecules, specifically proteins, an observation most often explained by convective mass transfer and the absence of small pores in the polymer scaffold. However, this conception is not sufficient to explain the performance of small molecules. This review focuses in particular on the preparation of (macro)porous polymer monoliths by simple free-radical processes and the key events in their formation. There is special focus on the fluid transport properties in the heterogeneous macropore space (flow dispersion) and on the transport of small molecules in the swollen, and sometimes permanently porous, globule-scale polymer matrix. For small molecule applications in liquid chromatography, it is consistently found in the literature that the major limit for the application of macroporous polymer monoliths lies not in the optimization of surface area and/or modification of the material and microscopic morphological properties only, but in the improvement of mass transfer properties. In this review we discuss the effect of resistance to mass transfer arising from the nanoscale gel porosity. Gel porosity induces stagnant mass transfer zones in chromatographic processes, which hamper mass transfer efficiency and have a detrimental effect on macroscopic chromatographic dispersion under equilibrium (isocratic) elution conditions. The inherent inhomogeneity of polymer networks derived from free-radical cross-linking polymerization, and hence the absence of a rigid (meso)porous pore space, represents a major challenge for the preparation of efficient polymeric materials for the separation of small molecules.

We have investigated the free-radical copolymerization dynamics of styrene and divinylbenzene in the presence of micro- and macro-porogenic diluents in 100 μm I.D. sized molds under conditions of slow thermal initiation leading to (macro)porous poly(styrene-co-divinylbenzene) monolithic scaffolds. These specifically designed experiments allowed the quantitative determination of monomer specific conversion against polymerization time to derive the porous polymer scaffold composition at each desirable copolymerization stage after phase separation. This was carried out over a time scale of 3 h up to 48 h polymerization time, enabling the efficient and repeatable termination of the polymerization reactions. In parallel, the porous and hydrodynamic properties of the derived monolithic columns were thoroughly studied in isocratic nano-LC mode for the reversed-phase separation of a homologous series of small retained molecules. At the optimized initiator concentration, polymerization temperature and time, the macroporous poly(styrene-co-divinylbenzene) monoliths show a permanent mesoporous pore space, which was readily observable by electron microscopy and indicated by nitrogen adsorption experiments. Under these conditions, we consistently find a polymer scaffold composition which suggests a high degree of cross-linking and thus minimum amount of gel porosity. These columns reveal a retention-insensitive plate height in the separation of small retained molecules which only slightly decreases at increased linear mobile phase velocity. As the polymerization progresses, a build-up of less-densely cross-linked material occurs, which is directly reflected in the observed consistent increase in retention and plate heights. This leads to a significant deterioration in overall isocratic separation performance. The decrease in performance is ascribed in particular to the increased mass transfer resistance governing the monoliths’ performance over the whole linear chromatographic flow velocity range at polymerization times significantly higher than that of phase separation. The performance of the optimized monoliths only becomes limited by fluid dispersion due to the poorly structured macroporous pore space.

Molecularly imprinted membranes are known to be applicable as recognition elements in separation, extraction and sensors, however, not as catalysts. In this paper, two different formats of molecularly imprinted membranes were generated and used as catalysts in a dehydrofluorination reaction. The first format was based on cellulose filter membranes which were coated with a polymer imprinted with a transition-state analogue of the chosen reaction. Alternatively, ground bulk polymers have been incorporated in polyvinyl alcohol (PVA) matrices on cellulose membranes. Both types of membranes were evaluated in membrane reactors. Either the substrate solution was pumped once only through the membrane, or the substrate solution was recirculated through the membrane. The coated membranes did not show any specific catalytic effect when comparing the molecularly imprinted with a non-imprinted control polymer membrane. Nevertheless, the PVA membranes containing the imprinted polymer particles showed specific catalytic effects, compared to PVA membranes with incorporated non-imprinted control polymer particles.

Molecularly imprinted polymers (MIPs) have been synthesised and applied as catalysts in the Diels-Alder cycloaddition of hexachlorocyclopentadiene and maleic acid. For this purpose, MIPs were generated either via bulk polymerisation, or with templates immobilised on silica particles leading to MIP shells. The performances of these differently produced MIPs were compared. MIPs obtained from bulk polymers did not show any higher catalytic activity than their respective non-imprinted control polymer (CP) particles. In contrast, the MIP shells have led to a product formation threefold as high as observed when using control polymer shells. Moreover, the catalytic effects of these MIP shells were noticeably higher than the ones of the bulk MIPs.

A new and fast technique for screening combinatorial libraries of molecularly imprinted polymers is presented. The procedure is based on commercially available membrane modules which are rinsed with pre-polymerization imprinting mixtures. After the in situ polymerization and generation of MIP films on the PTFE membranes within the modules, the membranes are evaluated in terms of affinity towards the target molecule (template) R-(-)-phenylbutyric acid. Therefore, after template extraction from the freshly produced membranes a solution of this target molecule is flushed through the module. By analyzing the remaining analyte concentration in the permeate, the amount of analyte adsorbed on the membrane can be calculated and related to specific interactions with the molecular imprints. By this means, optimized recipes in terms of cross-linker to template ratios could be obtained in combination with the optimal porogen, when screening p-divinylbenzene or ethylene glycol dimethacrylate as cross-linker and porogens like acetonitrile, dimethylsulfoxide and methanol.

Molecularly imprinted polymers (MIPs) are applicable in a variety of different configurations. For example, bulk polymers imprinted with β-lactam antibiotics are presented to be used as stationary phases for the chromatographic separation of β-lactam antibiotics with both aqueous and organic mobile phases. However, in some analytical applications, monosized spherical beads are preferred over the currently used ground bulk polymers. A precipitation polymerization technique allows preparation of monosized spherical imprinted beads with diameters down to 200 nm having excellent recognition properties for different target molecules. Nevertheless, with current imprinting protocols a substantial amount of template has to be used to prepare the polymer. This can be problematic if the template is poorly soluble, expensive or difficult to obtain. It is shown that for analytical applications, the functional monomer:template ratio can be drastically increased without jeopardizing the polymer’s recognition properties. Furthermore, a substantial reduction of the degree of crosslinking is demonstrated, resulting in much more flexible polymers that are useful for example the preparation of thin imprinted films and membranes for sensors. Apart from analysis, MIPs also are applicable in chemical or enzymatic synthesis. For example, MIPs using the product of an enzyme reaction as template are utilized for assisting the synthetic reaction by continuously removing the product from the bulk solution by complexation. This results in an equilibrium shift towards product formation.

In molecular imprinting (MI), interactive monomers and suitable cross-linking agents are polymerized in the presence of a template. Once the template has been removed, the remaining space acts as a highly specific binding site for the template or analogs thereof, due to the unique three-dimensional arrangement of interaction points. Several steps are involved in producing such a polymer coat inside a capillary electrophoresis capillary. First, the silanization of the inner surface of the capillary with a suitable silane is necessary, to link a monolayer of unsaturated groups suitable for polymerization to the capillary surface. These monomeric groups are then integrated into the three-dimensional polymer coat produced in the next step. MI-capillary coatings ideally are highly porous and of a thickness, δ, which is smaller than the inner radius, r, of the capillary in question. Porous polymer networks can be produced by dispersive polymerization using a suitable solvent (porogen). However, the exact conditions for producing a coating suitable for capillary zone electrophoresis had to be determined experimentally. Seven porogens, namely hexane, toluene, tetrahydrofuran, acetonitrile, CHCl3, dimethyl sulfoxide and dimethylformamide, and two cross-linkers, namely ethyleneglycoldimethacrylate and divinylbenzene, at concentrations of between 5 and 20% (v/v) were investigated. In about 20% of the combinations, a polymer coat of the desired qualities was obtained. The applicability of the MI capillaries to specific separations was demonstrated for the separation of a racemic mixture of S(+)- and R(−)-2-phenylpropionic acid. trans-3(3-Pyridyl)-acrylic acid was used as the interactive monomer in this case.

Macroporous monolithic poly(butyl methacrylate-co-ethylene dimethacrylate) stationary phases were synthesized in the confines of 100 microm I.D. fused-silica capillaries via a free radical copolymerization of mono and divinyl monomeric precursors in the presence of porogenic diluents. These columns were used in order to determine their suitability for the reversed-phase separation of small molecules in isocratic nano-LC mode. Carefully designed experiments at varying realized phase ratio by a terminated polymerization reaction, as well as content of organic modifier in the mobile phase, address the most significant parameters affecting the isocratic performance of these monoliths in the separation of small molecules. We show that the performance of methacrylate-based porous polymer monoliths is strongly affected by the retention factor of the analytes separated. A study of the porous and hydrodynamic properties reveals that the actual nature of the partition and adsorption of the small analyte molecules between mobile and stationary (solvated) polymer phases are most crucial for their performance. This is due to a significant gel porosity of the polymeric stationary phase. The gel porosity reflects stagnant mass transfer zones restricting their applicability in the separation of small molecules under conditions of strong retention.

The chapter describes the concept of molecular imprinting. This technology allows the fabrication of artificial polymeric receptors applicable in many areas of biotechnology. Polymers imprinted with selected template molecules can be used as specific recognition elements in sensors or as selective stationary phases in affinity chromatography or in capillary electrochromatography. However, also in solid phase extraction or immunoassays these polymers (MIP) are able to compete with traditional materials such as biological antibodies. Furthermore, polymers molecularly imprinted with so-called transition state analogue templates can be applied as catalysts. In other words, these kind of polymers may be used as artificial antibodies (plastibodies) or biomimicking enzymes (plastizymes). Compared to their biological counterparts, MIP offer different advantages such as simplicity in manufacturing and durability. Thus, the author expects MIP to have a major impact on the whole area of biotechnology.

Molecular imprinting is a way of creating polymers bearing artificial receptors. It allows the fabrication of highly selective plastics by polymerizing monomers in the presence of a template. This technique primarily had been developed for the generation of biomimetic materials to be used in chromatographic separation, in extraction approaches and in sensors and assays. Beyond these applications, in the past few years molecular imprinting has become a tool for producing new kinds of catalysts. For catalytic applications, the template must be chosen, so that it is structurally comparable with the transition state (a transition state analogue, TSA) of a reaction, or with the product or substrate. The advantage of using these polymeric catalysts is obvious: the backbone withstands more aggressive conditions than a bio material could ever survive. Results are presented showing the applicability of a molecularly imprinted catalyst in different kinds of chemical reactors. It is demonstrated that the catalysts can be utilized not only in batch but also in continuously driven reactors and that their performance can be improved by means of chemical reaction engineering.

Molecularly imprinted polymers (MIPs) to penicillin V or oxacillin were prepared, and their recognition properties were investigated, both in organic and aqueous phases. The resulting MIPs proved to be efficient in distinguishing between different penicillins (penicillin V, penicillin G and oxacillin), but could also be prepared to recognise the penicillins as a group. The results indicate that MIPs can be used to prepare either selective or general recognition matrices for penicillins, which can be of potential use in separation and detection applications.