Core–corona inversion of micelles of diblock copolymer poly(acrylic acid)‐block‐poly(N‐isopropylacrylamide) (PAA‐b‐PNIPAM), has been successfully realized by switching either pH or temperature. The strong interaction of doxorubicin with the PAA block and the pH‐sensitive drug release from the polymer make the system very useful as a controlled drug delivery system. The encapsulation of hydrophobic Nile Red molecules above the lower critical solution temperature of PNIPAM suggests that this polymer may be useful for removing hydrophobic pollutants.
Here, the formation of nanoparticles based on a microemulsion approach and the use of polymer surfactants are described. Therefore, two amphiphilic poly(2‐oxazoline) block copolymers P1 and P2 with alkyne groups in their hydrophobic block have been synthesized by ring‐opening, cationic polymerization. The polymers P1 and P2 are employed in a microemulsion process to stabilize the particle core by core cross‐linking of 1,6‐hexanediol diacrylate (HDDA) using either AIBN as azo‐initiator or 2‐propanethiol as a photo‐initiator for the polymerization reaction. The results show that particle size can be controlled by sonication time, the hydrophilic–hydrophobic balance of the polymer surfactant, and the ratio of polymer surfactant versus HDDA giving access to water‐soluble nanoparticles in a size range of 10–70 nm.
This work aims to improve the outstanding thermal and mechanical properties of commercialized wholly aromatic polyamide fibers (i.e., aramids), by crosslinking the materials. The introduction of a reactive azide group into the polymer structure leads to functional aramids. Crosslinking processes can be easily performed using an inexpensive thermal treatment after fiber spinning with current spin production facilities.
Silicone‐based dielectric elastomers are promising dielectric electroactive polymers (DEAPs) applicable to various actuator applications. However, the lack of information concerning their long‐term performance still limits their industrial use. Here, the time‐dependent behavior of silicon‐based DEAPs under electromechanical cycling is investigated. A series of thin silicone films prepared with different stoichiometric imbalances are coated with compliant silver nanowire electrodes and then electromechanically cycled under alternating voltage (Vpp = 2 kV, VDC = 1 kV) over 105 cycles. Afterward, changes in cross‐linking density, elastic modulus, permittivity, and breakdown behavior are examined. With increasing load cycles, electrically induced cross‐linking of the hydrosilane groups occurs, which leads to increased cross‐linking density of the material. Concomitantly, increase in elastic modulus and decrease in permittivity are observed, resulting in a significant deterioration of actuation performance. The measured breakdown strength, which is related to an extrinsic breakdown strength based on electromechanical instability, increases too.
Pure cross‐linked spherical micelles, nanowires, and vesicles are successfully fabricated from poly(2‐hydroxypropyl methacrylate‐b‐p‐(methacryloxyethoxy)benzaldehyde)s (PHPMA–b–PMAEBAs) through reversible addition‐fragmentation chain transfer dispersion polymerization of MAEBA in methanol using PHPMA as a macro‐CTA and subsequent cross‐linking. The cross‐linking reaction is conducted by stirring a mixture of 1,4‐butanediamine and the resultant nano‐objects in methanol at room temperature. For all polymerizations with feed molar ratios of MAEBA/PHPMA ranging from 75/1 to 240/1, the monomer MAEBA conversions are almost complete, and block copolymers with controlled molecular weight are obtained. The transmission electron microscopy, dynamic light scattering, and gel permeation chromatography results reveal that the following three factors significantly influence the morphology of the nano‐objects: the feed molar ratio of MAEBA/PHPMA, the copolymer concentration, and the degree of polymerization of PHPMA. The cross‐linked nano‐objects are very stable in good solvents, the spheres and nanowires slightly decrease in size after cross‐linking, whereas the vesicles slightly increase in size. The cross‐linked nano‐objects are stable in neutral solutions, but they dissociate in weekly acidic solutions. The loading of 1‐pyrenemethylamine (PMA) into the vesicles and the unloading of PMA from the vesicles are studied.
Novel structural motifs in macromolecular chemistry are introduced by the use of the Asinger multicomponent reaction. The combination of ammonia, acetone, α‐chloroisobutyraldehyde, and either water or sodium hydrosulfide, leads to an oxazoline or thiazoline scaffold, respectively, which is subsequently modified with 10‐undecenol and 10‐undecenoyl chloride to obtain heterocycle‐functionalized α,ω‐dienes. These substrates are used as monomers in an acylic diene metathesis (ADMET) or thiol‐ene step‐growth polymerization. The thus‐obtained polymers are studied in post‐polymerization modifications, like hydrogenation and oxidation. Here, the thiazolidine‐ and oxazolidine‐containing polymers show dramatically different chemical stability due to the heterocyclic moieties.
In this study, the electroluminescent (EL) properties of electrochemically cross‐linkable, terthiophene terminated poly(benzyl ether) dendrimers (G0‐3T and G1‐3T DNs) are investigated. In noncross‐linked 3T DNs, there is either no emission or a low‐intensity emission due to poor charge transfer of the isolated terthiophene (3T) oligomers at the periphery of the DNs. However, increase in the length of conjugation via electrochemical cross‐linking leads to the emission of a yellowish color. It is seen that the emission of this color is dependent on the dendritic structures and effectively controlled charge trapping. Thus, these results suggest that the dendritic molecular structure, which is associated with the conjugated length of the emissive peripheral units and the generation of the dendrimers, is an important factor in controlling EL properties.
In this paper, “star anise”‐like anisotropic micelle (AM) from direct aqueous self‐assembly of poly(ethylene oxide)‐block‐poly(p‐dioxanone) amphiphilic diblock copolymer is presented. By adding poly(ethylene imine) (PEI), the AM shows morphological change from “star anise” to swollen sphere. The mechanism of PEI‐triggered morphological transition involving complexation and weakening of crystallizability is revealed.
The synthesis of three different electron‐deficient internal alkynes for the metal‐free 1,3‐dipolar azide–alkyne cycloaddition is shown. The alkynes are polymerized with several multifunctional azides and the reaction enthalpy (ΔH) is investigated by differential scanning calorimetry (DSC). The mechanical properties of the resulting polymers are analyzed using nanoindentation. The polymerization results in hard materials with an E‐modulus of maximum 2.5 GPa, which make them interesting in particular for biomedical applications.
The study reports the fabrication of a free‐standing reactive macroinitiator thin film via simple layer‐by‐layer assembly and dissolution of the sacrificial layer. The resulting macroinitiator thin film can be postfunctionalized by grafting polymer brush from it. Since the thin film is free from any substrate, bifacial functionalization can be done on the free‐standing film. This approach is expected to significantly increase the functionality of free‐standing polymer brush for most applications like catalysis and sensor because of the increase in functional group density per area.
In the present work, the preparation of different styrene‐based polymer films containing small amounts of TPE and the evaluation of their photoluminescent behaviour is reported. When TPE is dispersed in a poor solvent or in a glassy PS matrix, the arrested intramolecular rotations of its aryls favour the strong emission of light centred at about 455–460 nm. Conversely, TPE fluorescence significantly weakens to a faint signal when good solvents or viscous but not glassy polymer matrices are used. Near‐field optical microscopy correlates the fluorescence behaviour with the different matrix morphologies. These results should be able to be used for developing a new tool for polymer traceability.
In this work, a multi‐scale approach with different analytical methods is applied to study the curing process and the structural properties of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin. This monomer, thermally cured using 4,4′‐diaminodiphenilsulfone (DDS) as hardener, is analyzed after 10, 45, 90, and 120 min of reaction time at 180 °C to obtain information on samples with different cross‐linking densities. Samples are also characterized after extraction in acetone in order to obtain structural information on the insoluble parts. For this purpose, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), solid‐state nuclear magnetic resonance (ss‐NMR), and positron annihilation lifetime spectroscopy (PALS) are employed. The importance of this multi‐method approach lies in the possibility to obtain a more complete knowledge of the investigated system, overcoming the limits inherent to the use of a single technique, through the correlation among results obtained from different structural investigation methodologies.
1‐Vinyl‐2‐(methoxymethyl)imidazole ( 6 ), 1‐vinyl‐2‐(ethoxymethyl)imidazole ( 7 ), 1‐vinyl‐2‐(propoxymethyl)imidazole ( 8 ), and 1‐vinyl‐2‐(butoxymethyl)imidazole ( 9 ) are synthesized through the etherification of 1‐vinyl‐2‐(hydroxymethylimidazole) ( 1 ) with corresponding alkyl halides ( 2–5 ). Corresponding homopolymers ( 10–13 ) are synthesized via free radical polymerization and investigated concerning their temperature‐dependent solubility in water. The homopolymer 11 shows a lower critical solution temperature (LCST) behavior with a cloud point of 23 °C. Through copolymerization of 7 with N‐vinylimidazole ( 14 ), the cloud point is varied up to 42 °C.
The synthesis of metal‐containing polymers and block copolymers has led to a rapidly expanding field of research interest for manifold potential applications. Within this contribution, some recent advances in the field of side‐chain ferrocene‐containing polymers focusing on poly(vinylferrocene) and poly(ferrocenyl methacrylates) are presented. The synthetic developments shown focus on living and controlled polymerizations, as well as surface‐initiated polymerization strategies. First attempts and recent developments for these novel redox‐responsive materials toward feasible applications are addressed.
The Passerini three‐component reaction is applied to synthesize, in a one‐step procedure, diverse asymmetric α,ω‐dienes containing an acrylate and a terminal olefin. Such monomers are well known to undergo head‐to‐tail acyclic diene metathesis (ADMET) polymerization due to the high cross‐metathesis selectivity between acrylates and terminal olefins. Additionally, amphiphilic block copolymers are synthesized using a monofunctional PEG480 monoacrylate, which acts as a selective chain‐transfer agent during the polymerization process. Thus, control over the molecular weight of the amphiphilic ADMET polymers is shown by using different ratios of monomer and chain‐transfer agent. All the polymers are thoroughly characterized, and their ability to form nanoparticles in aqueous solution is studied.
Herein, a novel coil‐rod‐coil triblock copolymer with the coil blocks composed of poly(ethylene glycol) methyl ether and the rigid midterm block alternatively connected with isophorone diisocyanate and isophorone diamine is developed. The triblock copolymer can self‐assemble into ellipsoidal micelles in 1‐methyl‐2‐pyrrolidinone. After the addition of a second coil‐selective solvent (water) to the micellar solutions, these ellipsoidal micelles can further transform into chain‐like nanostructures. The self‐assembly behavior is highly influenced by the additional order of the solvents, which is considerably due to the impacts of the hydrogen‐bonding urea groups and rigid motifs. The transition of the ellipsoidal micelles to chain‐like nanostructures is governed by the water molar fractions. The sizes of the chain‐like nanostructures increase first and then decrease with the growth of the water molar fractions in the mixed solutions.
An efficient way for covering various surfaces with poly(lactic acid) (PLA) is discussed. In a first step, the material is coated with polydopamine (PDA) by air oxidation of dopamine. The resulting PDA layer acts as an initiator for ring‐opening polymerization (ROP) of lactide resulting in an outer PLA shell. Since PDA sticks to almost every solid material, the methodology has a wide scope. The strategy is demonstrated with magnetic nanoparticles and non‐magnetic powders.
Thermally reduced graphene modified with cationic ammonium ions (AAG)—affording a stable dispersion in water—self‐assembles well by electrostatic interaction on the surface of anionic poly(methyl methacrylate) (PMMA) particles of various sizes, by simple mixing in water. An interconnected 3D electrically conductive network of AAG is effectively generated in the composite when the self‐assembled composite is compression molded. The AAG network becomes wide‐meshed and electrical conduction is improved when the PMMA particle size increases, exhibiting a percolation threshold of electrical conductivity as low as 0.06 vol%. In contrast, the protection of PMMA from oxidation by air is more effective when the network is fine‐meshed.
A series of multiarmed and multicomponent miktoarm (μ‐) star polymers have been successfully synthesized by developing a new iterative methodology based on a specially designed linking reaction of the block copolymer in‐chain anions, whose anions are positioned between the blocks, with α‐phenylacrylate (PA)‐functionalized polymers. The iterative methodology involves the following two reaction steps: a) introduction of two different polymer segments by the linking reaction of a block copolymer in‐chain anion with a PA‐functionalized polymer and b) regeneration of the PA reaction site. By repeating this reaction sequence, two different polymer segments are advantageously and successively introduced into the μ‐star polymer. In practice, repetition of the reaction sequence affords well‐defined 3‐arm ABC, 5‐arm ABCDE, 7‐arm ABCDEFG, and even 9‐arm ABCDEFGHI μ‐star polymers, composed of polystyrene, polystyrenes substituted with functional groups, polyisoprene, and poly(alkyl methacrylate) arms, respectively.
The variation of the drift mobility of positive and negative charge carriers in films of anthracene‐containing poly(p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene)s ( AnE‐PVs ), differently substituted, is investigated as a function of the applied electric field. Branched 2‐ethylhexyl and linear alkoxy side chains of different lengths are considered, as well as well‐defined and random distributions of lateral substituents. The same conditions are used both for the deposition of the polymer films and for their characterization, which allows for the establishment of a clear relationship between the chemical structure and the charge carrier mobility.
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