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Macromolecular Rapid Communications - published by
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... is one the most cited journals publishing original research in general macromolecular science. Each original article is commented on by current experts in the field. The commentary describes the role of each paper in the development of the particular area of polymer science and the historical background, and significance of the article.
Macromolecules - published by
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Focuses on all fundamentals of polymer science, including synthesis, polymerization mechanisms and kinetics, chemical modification, and solution/melt/solid-state characteristics, as well as surface properties of organic, inorganic, and naturally occurring polymers.
Macromolecular Chemistry and Physics - published by
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The journal contains original research papers in all topical areas of polymer chemistry and physics. Outstanding macromolecular science research is presented in the form of strictly peer-reviewed Full Papers. Macromolecular Chemistry and Physics also includes Highlights, Book Reviews, Essays, Macromolecular News and Conference Reports.
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... explores the interactions of macromolecules with biological systems and their environments as well as biological approaches to the design of polymeric materials. Cutting-edge research at the interface of polymer science and biological sciences.
Aktuelle wissenschaftliche Fachartikel der
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Reversibly cross-linked core-shell-corona micelles based on a triblock copolymer composed of poly(aliphatic ester), polyphosphoester, and poly(ethylene glycol) are reported. The triblock copolymer is synthesized through consecutive ring-opening polymerization of [epsiv]-caprolactone and 2,4-dinitrophenylthioethyl ethylene phosphate, followed by conjugation of poly(ethylene glycol). After deprotection under mild conditions, the amphiphilic polymer forms core-shell-corona micelles with free thiols in the shell. Cross-linking of the micelles within the shell reduces their critical micellization concentration and enhances their stability against severe conditions. The redox-sensitive cross-linkage allows the facilitated release of entrapped anticancer drugs in the cytoplasm in response to the intracellular reductive environment. With enhanced stability during circulation after administration, and accelerated intracellular drug release at the target site, the biocompatible and biodegradable shell-cross-linked polymeric micelle is promising as a drug vehicle for cancer chemotherapy.
A simple and direct method for derivatization of solid polysaccharides is presented. The novel methodology is based on the combination of organic acid-catalyzed esterification or etherification and photochemical thiol-ene click derivatization of a heterogeneous polysaccharide. The solid cellulose was "organoclick" modified with aryl, alkyl and polyester groups, respectively. The modification allows for a highly modular and metal free surface modification of solid polysaccharides.
UV irradiation of chloromethyl styrene simultaneously crosslinks the polymer and generates aldehyde groups that can be employed for polymer surface functionalization through aldehyde-imine/hydrazone chemistry. Using this method, we successfully have functionalized nanoimprinted polymer patterns with dyes, nanoparticles, and enzymes. These surfaces were characterized by infrared (ATR-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), fluorescence microscopy, and enzymatic activity assays.
Here, we present a new class of terpyridine complexes of the transition-metal ions, iron(II), ruthenium(II), and osmium(II), overcoming the poor emission properties typical for this class of polypyridyl complexes. These complexes show, besides an increased room-temperature emission quantum yield and a prolonged lifetime of the metal-to-ligand charge-transfer (MLCT) states, dual emission from two well-separated excited states of the same molecule. These experimental findings are attributed to a highly stabilized ligand chromophore, where photoinduced excited-state planarization causes an enhancement of electron delocalization. This planarization, in turn, reduces the potential energy of the S1 state and minimizes electronic coupling to the MLCT state, which is prone to non-radiative deactivation via metal-centered excited states. Due to their dual emission the complexes presented here show emission covering the entire Vis spectral range upon excitation of the [pi][pi]* states in the near UV. Thus, by structurally tuning the electronic coupling of the [pi][pi]* and the MLCT states a new synthetic route toward white emitters, which can subsequently be incorporated into polymers, is opened.
A new series of shape-persistent metallomacromolecules G0 and G1 as well as corresponding ligands, based on thiophene-functionalized bisterpyridine-Ru(II) with truxene moieties, as the nodes, were developed. All new compounds were fully characterized by 1H, COSY, and 13C NMR, as well as MALDI-TOF MS. Their photophysical properties revealed that the branched scaffold resulted in high molar absorption coefficients and broad absorption making these materials potential candidates for light-harvesting.
PEDOT nanospheres with an average diameter of about 100 nm were chemically synthesized using APS as the oxidant in the presence of SDBS and Cu2O, respectively. It was found that Cu2O is crucial to forming uniform PEDOT nanospheres because only granular PEDOT was obtained in the absence of Cu2O. It is proposed that the PEDOT nanospheres are self-assembled by a cooperation effect of SDBS as the micelle soft-template and Cu2O as the stabilizer of the spherical micelles. Additionally, the PEDOT nanospheres are soluble in some organic solvents, such as THF, DMF and DMSO, which is of benefit for fabrication of electronic and photonic devices.
High oleic sunflower oil, a renewable raw material consisting of triglycerides with internal C[double bond]C-double bonds, was polymerized via acyclic triene metathesis (ATMET) to highly branched and functionalized polyesters. If the Hoveyda-Grubbs second generation catalyst was used and methyl acrylate was introduced as a chain stopper, the molecular weight of the obtained polymers could be tuned by varying the ratio of the triglyceride and methyl acrylate. Using the first generation Grubbs catalyst for the polymerization of high oleic sunflower oil, no cross-linking was observed, even without the use of a chain stopper. The resulting branched materials were characterized by GPC, 1H and 13C NMR, and ESI-MS.
A series of star block copolymers were prepared through nitroxide-mediated radical polymerization (NMRP) from polyhedral oligomeric silsesquioxanes (POSS) nanoparticle by core-first polymerization. Eight N-alkoxyamine groups were incorporated onto the eight corners of a POSS cube through quantitative hydrosilylation through addition of octakis(dimethylsiloxy)silsesquioxane (Q8M8H POSS) with 1-(2-(allyloxy)-1-phenylethoxy)-2,2,6,6-tetramethylpiperidine (allyl-TEMPO) and Karstedt's agent (a platinum divinylsiloxane complex) was used as a catalyst. Octa-N-alkoxyamines POSS (OT-POSS) were used as platform to synthesize star polystyrene-POSS ((PS)8-POSS) homopolymer and diblock copolymers of poly(styrene-block-4-vinylpyridine)-POSS ((PS-b-P4VP)8-POSS) and poly(styrene-block-acetoxystyrene) ((PS-b-PAS)8-POSS) through NMRP. In addition, subsequent selective hydrolysis of the acetyl protective group of (PS-b-PAS)8-POSS, the poly(styrene-block-vinyl phenol) ((PS-b-PVPh)8-POSS) with strong hydrogen bonding group was obtained. The detailed chemical structure and self-assembled structures of these star block copolymers based on POSS were characterized by 1H NMR, FTIR, SEC, TEM, and SAXS analyses.
The synthesis of the 1st generation dendrimer 1,3,5-{trans-[Ru(C[equiv]C-3,5-(trans-[Ru(C[equiv]CPh)(dppe)2(C[equiv]CC6H4-4-(E)-CH[double bond]CH)])2C6H3)(dppe)2(C[equiv]CC6H4-4-(E)-CH[double bond]CH)]}3C6H3 proceeds by a novel route that features Emmons-Horner-Wadsworth coupling of 1,3,5-C6H3(CH2PO(OEt)2)3 with trans-[Ru(C[equiv]CC6H4-4-CHO)Cl(dppe)2] and 1-I-C6H3-3,5-(CH2PO(OEt)2)2 with trans-[Ru(C[equiv]CPh)(C[equiv]CC6H4-4-CHO)(dppe)2] as key steps. The stilbenylethynylruthenium dendrimer is much more soluble than its ethynylated analog 1,3,5-{trans-[Ru(C[equiv]C-3,5-(trans-[Ru(C[equiv]CPh)(dppe)2(C[equiv]CC6H4-4-C[equiv]C)])2C6H3)(dppe)2(C[equiv]CC6H4-4-C[equiv]C)]}3C6H3 and, in contrast to the ethynylated analog, is a two-photon absorber at telecommunications wavelengths.
As one of the most promising optoelectronic materials, polymers that contain phosphorescent IrIII complexes have attracted more and more interest in recent years. They are a class of well-known electroluminescent materials with excellent performance. So far, efficient green-, red-, and white-emitting polymer light-emitting diodes based on polymers with on-chain IrIII complexes have been realized successfully. For the realization of this class of polymer material, IrIII complexes (as energy guest) can be introduced into the main-chain or side-chain of polymers (as energy host). In this article, we summarize the design principles, synthetic routes, structure-property relationships, and applications in optoelectronic devices of polymers that contain phosphorescent IrIII complexes.
The molecular characteristics of poly(N-isopropylacrylamide) (PNIPA), prepared by free-radical polymerization using an aqueous redox initiator and reaction conditions comparable to those used in the synthesis of nanocomposite gels, were investigated by altering the monomer concentration ([NIPA]) and the polymerization temperature (Tp) across the transition temperature (LCST). When Tp<LCST, there is a critical [NIPA] (=n*) above which PNIPA partially forms gels in the absence of a chemical crosslinker, and the gel fraction increases with increasing [NIPA] and decreasing Tp. In the range of n<n*, the molecular weight of soluble PNIPA correlated well with [NIPA]. When Tp>LCST, gels were not formed regardless of [NIPA]. The structure and mechanism of formation of self-crosslinked PNIPA gels are discussed.
Rigid anisotropic crosslinkers have been shown to decrease the nematic order and the transition temperatures of main-chain liquid crystalline elastomers (MCLCEs). In order to look into this phenomenon, the state of order of an anisotropic crosslinker in an MCLCE was investigated separately from that of the matrix. For this purpose, multifunctional perylene derivatives were synthesized and used as a crosslinker and as a reference mesogen probe. Their states of order were measured by their dichroism, and were compared to that of the MCLCE matrix. A systematically lower degree of order was observed for the crosslinker in comparison to the matrix, both when attached to and dissolved in the network.
Stoichiometric ionically bonded side-chain polymer complexes of poly(styrene sulfonate) and quaternary ammonium-functionalised azo-containing surfactomesogens were exposed to controlled humidity atmosphere, to organic non-solvents (acetone, THF, ethyl acetate) and to a good solvent (DMF) for the complex. This modifies or increases the packing order, and includes induction of a crystal-like lamellar structure that is amenable to photoisotropisation. The molecular packing order influences photoinduced birefringence relaxation. Conditions for frozen-in morphologies are discussed in the light of higher temperature data. The observed diversity of phase changes upon solvent exposure is comparable to what is observed in surfactant-polyelectrolyte complexes.
The structure of adsorption layers of amphiphilic block and block-like copolymers of poly(isobornyl acrylate) and poly(acrylic acid) on the surface of hydrophilic titanium dioxide and hydrophobic copper phthalocyanine (CuPc) pigments in an aqueous dispersion has been studied by the electrokinetic sonic amplitude (ESA) method. The electroacoustic behaviour of the polyelectrolyte block copolymer-coated particles could be described in the context of the polymer gel layer theory. The polymer layer around the particles was found to be much thinner for CuPc as compared to the TiO2 substrate. This is attributed to differences in the adsorption mechanism and the composition of the adsorption layer normal to the substrate surface. Adsorption models were established that consider effects of the copolymer structure.
There is a significant knowledge gap in the degradation of poly(methyl methacrylate) (pMMA) under conditions experienced by surface coatings in the harsh Australian environment. In the current study pMMA model compounds were exposed to 95 °C temperatures and high UV radiation (1 kW · m-2), separately as well as in combination. Contrary to the findings of previous studies, degradation proceeds in these conditions via a non-radical cyclic mechanism. The mechanism was further confirmed by synthesis and degradation of ethylene-oxide-terminated pMMA, an intermediate product in the cycle. Electrospray ionisation mass spectrometry analysis of thermally degraded samples after 155 weeks shows degradation consistent with the proposed cycle in vinyl-terminated pMMA, while saturated pMMA was shown to be stable after the same period. Saturation delayed the UV-induced degradation, yet these compounds still displayed some slight degradation after 52 weeks, confirming the terminal vinyl bond in pMMA as a weak point. Combined UV and thermal radiation after 56 weeks showed degradation of both pMMA samples, with the vinyl-terminated sample also exhibiting crosslinking. The combination of thermal and UV radiation also caused acceleration of degradation, shown by a comparison of the polymer samples after [ap]60 weeks.
The influence of the doping level in the formation of specific interactions between plasmid DNA and PEDOT is investigated using experimental assays and theoretical calculations. Electrochemical methods are used to prepare polymer samples with oxidation degrees ranging from 0.14 to 1.05 positive charges per repeating unit. A combination of experimental and theoretical results are used to propose a mechanism for the formation of DNA/conducting polymer complexes, which consists of the initial stabilization of the adducts through non-specific interactions followed by small structural re-arrangements that allow to be established specific hydrogen bonds involving the polar groups of the conducting polymer and selected DNA bases.
A nonconjugated N-vinyl monomer, N-vinylphthalimide (NVPI), was copolymerized with various comonomers via reversible addition-fragmentation chain transfer (RAFT) process. Two different chain transfer agents (CTAs), O-ethyl-S-(1-ethoxycarbonyl) ethyldithiocarbonate (CTA 1) and benzyl 1-pyrrolecarbodithioate (CTA 2), were compared for these copolymerizations with 2,2[prime]-azobis(isobutyronitrile) as an initiator. The effects of the nature of CTA, the comonomer structure, and solvent on the copolymerization were investigated in terms of the controlled character of the copolymerization and alternating structure. The copolymerization of NVPI and N-isopropylacrylamide using CTA 2 in DMF or MeOH afforded well-defined copolymers with predominantly alternating structure, controlled molecular weights, and low molecular mass distributions.
The influence of Hofmeister salts was investigated on the cloud point of three poly(2-oxazoline)s, namely poly(2-ethyl-2-oxazoline) [PEtOx], poly(2-n-propyl-2-oxazoline) [PnPropOx], and poly(2-isopropyl-2-oxazoline) [PiPropOx]. In addition, a comb polymer based on oligo-2-ethyl-2-oxazoline side chains and a methacrylate backbone (POEtOxMA) was included in this investigation. It was found that the ionic response of the poly(2-oxazoline)s strongly depends on their hydrophilicity. The comb polymer POEtOxMA revealed a strikingly similar response to the salts as linear PEtOx even though the cloud points of the polymers in water differ. This indicates that the architecture does not significantly influence the effect of the Hofmeister ions, even though there is a difference in the absolute cloud point.
This paper reviews the precise synthesis of many-armed and multi-compositional star-branched polymers, exact graft (co)polymers, and structurally well-defined dendrimer-like star-branched polymers, which are synthetically difficult, by a commonly-featured iterative methodology combining living anionic polymerization with branched reactions to design branched polymers. The methodology basically involves only two synthetic steps; (a) preparation of a polymeric building block corresponding to each branched polymer and (b) connection of the resulting building unit to another unit. The synthetic steps were repeated in a stepwise fashion several times to successively synthesize a series of well-defined target branched polymers.
A triblock amphiphilic macrocycle consisting of a macrocyclic aromatic segment, a hydrophilic oligo(ethylene oxide) branch, and a hydrophobic alkyl dendron is successfully synthesized and characterized. The resulting cyclic amphiphile is observed to self-assemble into hollow double-layered capsules in aqueous solution, as confirmed by dynamic light scattering and cryogenic transmission electron microscopy investigations. The capsules are able to encapsulate hydrophobic guest molecules through aromatic interactions with high stability.
Bifunctional surfaces are micropatterned using a self-aligned, dual-purpose lithographic mask and pairs of conformally deposited iCVD polymers. A first layer is deposited, then physically masked and etched in oxygen plasma. A second layer is deposited with the mask still in place. Lift-off reveals the micropatterned surface. The thicknesses of the two layers are independently controlled so that the resultant surface displays both chemical and topographical contrast. The patterning scheme is independent of the polymers used and order of deposition. We use this scheme to create surfaces that spatially confine microcondensation, as well as chemical functionality. We also demonstrate microwells whose depth can be altered in response to a water stimulus.
In this work, we report how biodegradable triple-layered microparticles can be fabricated through a simple, reliable, and economical one-step solvent evaporation technique. Characterization of triple-layered PLGA (shell)/PLLA (middle layer)/EVA (core) microparticles was conducted and their formation mechanism was described. Subsequently, in vitro hydrolytic degradation of these microparticles was investigated. It was found that the PLGA shell degraded rapidly leaving behind double-walled microparticles of PLLA/EVA after 40 days. The middle PLLA layer degraded more rapidly than expected because of the migration of PLGA oligomers that created a hydrophilic and acidic microenvironment in the PLLA layer. These degradation results therefore provide important insights into how triple-layered microparticles degrade, and how their degradation characteristics affect the drug releasing properties of these novel microparticles.
Supramolecular star-shaped polymers are a class of materials that are formed by self-assembly of polymeric precursors. The resulting structures combine the beneficial properties of conventional star-shaped polymers and (reversible) supramolecular interactions. We previously introduced [2 × 2] copper(I) grids of 3,6-di(2-pyridyl)-pyridazine (DPP) as structural motif to form the core of supramolecular star-shaped polymers. In the current work, this concept is expanded to star-shaped poly(ethylene glycol) (PEG) by end-functionalization of amine-functionalized PEG with DPP. The synthesis and characterization of PEG-DPP as well as the self-assembly into star-shaped supramolecular polymers upon copper(I) complexation are discussed in detail.
Synthetic glycopolypeptides have attracted much interest for application in biomedical field as they are structural mimics to the natural glycopeptides or glycoproteins. However, the synthesis methods toward glycopolypeptides are still few or less efficient. Herein, we present a facile route to preparation of glycopolypeptides with highly effective "glycosylation" by click postpolymerization modification. First, an alkyne-substituted N-carboxyanhydride (NCA) monomer was synthesized and subsequently polymerized to afford the polypeptide with "clickable" alkyne pendants. The alkyne-functionalized polypeptide was then "glycosylated" by click reaction of different sugar azides to the alkyne pendants with high efficiency. All the obtained glycopolypeptides were soluble and preferred [alpha]-helix conformation in water. Primary studies on the obtained glycopolypeptides binding with Con A lectin were assessed by turbidimetric assay. The more quantitive studies of the interactions between lectin proteins and the synthetic glycopolypeptides, and the application of these materials as the multivalent ligands are in progress.
This study reports the first PEO-coated polymer nanoparticles synthesis by miniemulsion polymerization of nano-emulsions prepared by the low-energy emulsification method called EIP. The surfactant used was Brij 98, a PEO based non ionic commercial surfactant. The partial phase diagram of the system water/Brij 98/styrene was first determined. The Emulsion Inversion Point technique was then used on the water/Brij 98/styrene system to the formation of styrene-in-water nano-emulsions. After miniemulsion polymerization, particle sizes as low as 36 nm were obtained. To the best of our knowledge, this method had not been used for polymerizable system up to now.
Using Monte Carlo simulations we show that the equilibrium properties of metallo-supramolecular micelles are determined by the competition of 2:1 and 1:1 metal-ligand complexation in the bulk and on the surface as well as steric interactions between the neighboring corona blocks attached to the surface. We predict that by increasing the association energy for the second metal-ligand bond, or decreasing the corona block length one can achieve a larger core surface coverage for metallo-supramolecular micelles. Compared to covalently bonded block copolymer micelles, we show that metallo-supramolecular micelles have smaller monomer and end group density, especially in the vicinity of the core, which may lead to experimentally observed aggregation.
Monodisperse hyper-crosslinked polystyrene nanospheres with ultrahigh specific surface area were successfully prepared by emulsifier-free miniemulsion polymerization and post-crosslinking. The specific surface area and the total pore volume of hyper-crosslinked nanospheres were increased with increasing the concentration of vinybenzyl chloride in monomer mixture. The hyper-crosslinked nanospheres exhibited excellent swelling capacity in thermodynamically good and poor solvent. Furthermore, the nanospheres with specific surface area of 1 223 m2 · g-1 adsorbed 2.13 wt.-% hydrogen at 163 K/1.5 MPa. Overall, the present study provided a simple method to prepare monodisperse microporous hyper-crosslinked polymer nanospheres.
Synthesis and characterization of a series of PAEs containing DPP units in the main chain are described. of the polymers was in the range 10 800-111 900. The polymers formed a deep blue solution in chloroform with absorption maxima between 589 and 645 nm and optical band gaps ranging from 1.61 to 1.74 eV. When excited at the absorption maxima, the polymer solutions showed red fluorescence with emission maxima between 656 and 676 nm. The polymers exhibited quasi-reversible oxidation process with HOMO energy levels between -5.60 and -6.17 eV. EL properties of three polymers were investigated with device configuration ITO/PEDOT:PSS/Polymer/LiF/Al. When appropriate bias voltage was applied, a red EL with a maximum brightness of 17.5-24 cd · m-2 could observe from the devices.
Surface-induced crystallization of high-density polyethylene in vertically aligned multiwalled carbon nanotube arrays has been investigated by means of scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). 1-mm long nanotube arrays are infiltrated by polyethylene solutions and then the system is allowed to crystallize under controlled conditions. Periodic disk-shaped polyethylene single crystals grow perpendicularly to the aligned nanotubes but do not completely fill the intertube spacing, forming oriented 3D porous structures. This unique morphology leads to low density, high nanotube mass fraction (up to 80 wt.-%) composites. Microstructure (WAXD) analysis shows that the nanotubes act as both orientation templates as well as nucleating agents for polyethylene crystallization creating orthorhombic and monoclinic forms, although the overall crystal structure is dominated by the orthorhombic form. Thermal analysis (DSC) shows that the nanocomposite exhibits multiple phase transitions during heating and cooling with a weak superheating and supercooling dependence on different scanning rates. Three phase structures have been identified and a possible model is proposed to explain the observed phenomenon.
PE/MMT nanocomposites were prepared through in situ polymerization using a nickel diimine catalyst supported on commercially available MMTs such as Cloisite Na+, Cloisite 30B, and Cloisite 93A. XRD patterns revealed that the layers of Cloisite 30B and Cloisite 93A were intercalated after treatment with TMA and the nickel diimine complex. The catalyst supported on Cloisite 30B showed high yields without additional activator and produced nanocomposites with high melting and decomposition temperatures. The thermal properties and crystallinity could be controlled by varying the clay content in the nanocomposite. The morphologies of the resulting particles and the dispersion of the MMT layers in the polymer matrix were characterized by SEM and TEM.
A new pH sensor, which consists of a fluorophore and gold nanoparticle (AuNP) attached to each chain end of a pH-sensitive polysulfonamide, respectively, is synthesized, and its pH sensitivity is investigated in terms of the fluorescent quenching efficiency of AuNP. Since the pH-sensitive polymeric linker exhibits a pH-induced coil-globule transition that is rapid enough to show a typical two-state transition, it shows drastic on-and-off quenching efficiency with variation of pH due to the change in the distance between fluorophore and AuNP. This AuNP-based pH sensor exhibits a well-defined on-and-off behavior at a small change in pH, and therefore can be used for an ideal alarm-type sensor.
PEO-based amphiphilic block copolymers that exhibit a pH responsive phase transition behavior are synthesized. The amphiphilic block copolymers show sharp phase transitions in the physiological pH (7.2) range of aqueous media. The block copolymers were efficient stabilizers for the preparation of superparamagnetic iron oxide nanoparticles in aqueous media. The resulting iron oxide nanoparticles in the size range of 5-30 nm showed a relatively good image on the basis of the results on their phantom test. All the materials were characterized by the combination of 1H NMR spectroscopy, size exclusion chromatography, UV/visible spectroscopic analysis, magnetization, transmission electron microscopy, electron diffraction, and X-ray diffraction pattern analysis.
The hot-stretching method has been well accepted for enhancing the electrical conductivity of conducting polymer films. High temperature is the prerequisite to soften the polymer to highly align and elongate the polymeric molecular chains. In this study, the cold-stretching method is proposed for the first time to enhance the conductivity of conducting polymeric films. Polyaniline (PANI) films are stretched at room temperature to different strain levels. It is observed that the applied strain has significant effects on the morphology, molecular chain structure, crystallinity, and crosslinking of the PANI films. As a result, the conductivity of PANI films is effectively increased by the cold-stretching process. Particularly, a maximum conductivity with an 18.4-fold increase in the direction parallel to the stretched direction is obtained when the elastic limit strain is applied. Compared to hot stretching, cold stretching is unique due to the extremely low dimensional change and very high efficiency achieved.
The homopolyester of isosorbide and cis-trans 1,4-cyclohexane dicarboxylic acid (CHDA) was prepared by three different methods, but only polycondensation of isosorbide and CHDA dichloride yielded a satisfactory molecular weight (corrected = 11 000 Da). For the best sample the MALDI-TOF mass spectrum revealed a high content of cycles. The homopolyester of CHDA and isomannide or isoidide was prepared analogously. For the homopolyesters of CHDA high glass transition temperatures were found (Tg = 146 °C for isosorbide, 133 °C for isomannide, and 115 °C for isoidide), whereas the polyester of isosorbide and succinic acid (SuA) has a Tg around 77 °C. Copolyester of isosorbide and various molar ratios of CHDA and SuA were prepared by two different methods, but only rather low molecular weights were obtained. SEC measurements with and without "universal calibration" revealed that the normal calibration with polystyrene overestimates the real molecular weights by 30-45%.
Surface-attached, photo-crosslinked gel films of a N-isopropylacrylamide copolymer were investigated in ethanol/water mixtures using a combination of surface plasmon resonance/optical waveguide spectroscopy with reversed WKB analysis. The solvent quality of the pure good solvents drops in their mixture and this co-nonsolvency effect shifts the transition temperature (Tc) in the µm-thin gel films from 32.8 °C in pure water to 29.7 °C with only 0.25 vol.-% ethanol. Between 20 and 70% ethanol and >10 °C (the practical temperature limit) the layers existed only in the collapsed state. A reentrant Tc of 40.2 °C was found at 70% ethanol while at higher ethanol volume fraction no Tc could be recorded.
Synthetic gene delivery vectors, especially cationic polymers have attracted enormous attention in recent decades because of their ease of manufacture, targettability, and scaling up. However, certain issues such as high cytotoxicity and low transfection efficiency problems have hampered the advance of nonviral gene delivery. In this study, we designed and synthesized brush-like amphoteric poly[isobutylene-alt-(maleic acid)-graft-oligoethyleneamine] capable of mediating highly efficient gene transfection. The polymers are composed of multiple pendant oligoethyleneimine molecules with alternating carboxylic acid moiety grafted onto poly[isobutylene-alt-(maleic anhydride)]. The polymer formed from pentaethylenehexamine {i.e., poly[isobutylene-alt-(maleic acid)-graft-pentaethylenehexamine)]} was able to condense DNA efficiently into nanoparticles of size around 200 nm with positive zeta potential of about 28-30 mV despite its amphoteric nature. Luciferase expression level and percentage of GFP expressing cells induced by this polymer was higher than those mediated with polyethyleneimine (branched, 25 kDa) by at least one order of magnitude at their optimal N/P ratios on HEK293, HepG2, and 4T1 cells. In vitro cytotoxicity testing revealed that the polymer/DNA complexes were less cytotoxic than those of PEI, and the viability of the cells after being incubated with the polymer/DNA complexes at the optimal N/P ratios was higher than 85%. This polymer can be a promising gene delivery carrier for gene therapy.
Two solution-processable metallopolyynes of platinum functionalized with the electron-deficient 4H-cyclopenta[2,1-b:3,4-b']dithiophen-4-one spacer and their model molecular complexes were synthesized and developed for the applications of polymer solar cells. These metallated polymers possess extremely low bandgaps of 1.44-1.53 eV which extend toward the near-infrared (NIR) range of the solar spectrum, and represent the lowest optical bandgap yet reported for platinum(II) metallopolyynes to date. The structural flexibility, processibility, and good photovoltaic performance make cyclopentadithiophenone-containing polymers prominent candidates for NIR photovoltaic applications.
Poly(ethylene glycol) (PEG)-based films, nanotubes, and nanotube arrays were successfully made using layer-by-layer (LbL) assembly ion-containing PEO derivatives on porous templates and planar substrates. PEG nanotubes are challenging to produce because PEG dissolves into solutions and solvents used during nanotube processing, but our techniques circumvent the issue. Nanotube dimensions were verified using microscopy and the average observed diameter was 155 nm. The PEG-based structures showed remarkable stability in water, salt water, and sodium hydroxide solution.
We present the first fast and facile microwave assisted synthesis of polyaniline (PANI) nanofibers ("MWA synthesis"). Under conventional synthesis (CS), the polymer was produced with 79.7% yield after 5 h at ambient temperature. However, under microwave irradiation, the nanofibers were produced with yield of 76.2% after only 5 min, i.e., with 78.8% after 20 min at ambient temperature. The FTIR and Raman spectra show the PANI structure in all samples either synthesized conventionally or in the microwave. SEM and TEM confirm the nanofibrillar morphology.
Dumbbell-shaped amphiphiles based on an elongated rod segment can self-assemble into planar networks with in-plane hexagonally ordered pores in aqueous solution. On increasing temperature, the 2D networks change into hollow capsules passing through the closed sheets as an intermediate structure due to a LCST behavior of the oligoether dendritic exterior. The primary driving force for this interesting feature seems to originate from a consequence of the energy balance between hydrophobic interactions of anisotropic rod segments and alkyl chains, and repulsive interactions between dissimilar blocks. This dynamic structural variation triggered by external stimuli in a self-assembling system can provide a useful strategy to create smart supramolecular materials and biomimetic systems.
We report the simple one-pot synthesis of size tunable zinc oxide nanoparticles (ZnO NPs) out of an organometallic ZnO precursor using the self-assembly of solution phase polystyrene-block-poly(2-vinylpyridine) micelles. The resulting hybrid material could be deposited on various substrates in a straightforward manner with the NPs showing size-dependent absorption and photoluminescence due to the quantum-size effect. We compare the results to the assembly of preformed NPs which are selectively incorporated in the poly(2-vinylpyridine) core of the micelles due to the high affinity of ZnO to vinylpyridine.
Graft copolymers with thermo-sensitive PNIPAAm backbone and hydrophilic PEtOxa graft chains demonstrated typical amphiphilic behavior. For specific compositions stable micelle-like aggregates were formed depending on the temperature. Applying long polyoxazoline side chains ( > 120), stable reversible micelle-like aggregates with hydrodynamic radii of 30-40 nm could be obtained between 33 and 55 °C. These graft copolymers have been successfully crosslinked by electron-beam irradiation in the micellar state yielding core/shell type nanogels with thermo-reversible swelling behavior. The temperature dependent volume change of the new thermo-responsive nanogels due to the phase transition of the PNIPAAm core has been verified by DLS.
Photoinduced microphase separation in block copolymers (BCP) was achieved for the first time, using a rationally designed diblock copolymer composed of two side-chain liquid crystalline polymers (SCLCP). The miscibility of the two blocks was promoted by the miscibility between the two types of mesognic side groups, while upon UV exposure inducing the trans-cis isomerization of azobenzene mesogens on one SCLCP, the shape incompatibility of bent cis isomers with an ordered liquid crystalline phase drove the separation of the two blocks resulting in a microphase separated morphology. This result shows the perspective of using light to process and organize BCP morphology and related nanostructures in a lithography-free manner.
The extraordinary mechanical and swelling/deswelling properties of nanocomposite (NC) gels are attributed to their unique organic (polymer)/inorganic (clay) network structure. In this study, poly(N-isopropylacrylamide) (PNIPA) was successfully separated from an NC gel network by decomposing the clay (hectorite) using hydrofluoric acid (HF). A very low HF concentration (0.2 wt.-%) was adequate for the decomposition of the clay without causing any damage to PNIPA. The separated PNIPA had a high (=5.5 × 106 g · mol-1). Also, was almost constant regardless of the clay concentration (Cclay = 1-25 × 10-2 mol · l-1), even though the properties of the NC gel varied widely over this Cclay range. Comparisons of NC gels, PNIPA, and SiO2-NC gels indicated that the clay platelets specifically play an important role in NC gels.
A modified synthesis of 25-allyl-26,27,28-trihydroxycalix[4]arene is reported. This calix[4]arene was utilized to prepare calix[4]arenes containing norbornene and calix[4]arene containing azo dyes and norbornene on their upper rims. The calixarene monomers were reacted with Grubbs' second generation catalyst to give poly(norbornenes) containing calixarenes. The poly(norbornenes) were determined to possess molecular weights between 45 100 and 116 200 with PDIs between 1.4 and 1.9. Thermal analysis showed that the azo dye containing polymers were less thermally stable than the non-azo dye containing polymers with decompositions beginning at 140 °C and 395 °C, respectively. The azo dye containing polymers displayed [lambda]max at 430 nm in THF solutions that underwent a bathochromic shift to 520 nm when acidified with HCl(g), due to the formation of the azonium ion.
In this paper, a facile route was designed to prepare a new AB2-type polymer P1 via simple Sonogashira coupling reaction, also its corresponding linear analog (P2) was obtained from AB monomer for comparison. Despite the relatively lower loading density of the effective chromophore moieties, P1 demonstrated higher second-harmonic coefficient (153.9 pm · V-1) than that of P2 (98.2 pm · V-1), due to the three-dimensional spatial isolation effect of the hyperbranched structure. The good results of P2 also indicated that the ladder shape may help to solve the problem existing in main-chain polymers, the low poling efficiency.
We demonstrate the formation of highly ordered hexagonal arrays of hybridized polystyrene-poly(4-vinyl pyridine), PS-PVP, micelles with controllable size by solvent annealing techniques. Because the formation of hybridized micelles was prohibited in the mixture solutions of two different-sized PS-PVP micelles, single-layered films with bimodal self-assemblies of small and large micelles were fabricated from the mixture solutions by adjusting their mixing ratios. When the single-layered films were solvent annealed by saturated vapor of tetrahydrofuran (THF), on the other hand, small and large PS-PVP micelles in the bimodal self-assemblies merged together to form hybridized micelles. In addition, the hybridized micelles arranged themselves in a highly ordered hexagonal array, the diameter and center-to-center distance of which were precisely adjusted by varying the mixing ratio of small to large micelles in the bimodal assemblies.
A series of donor-acceptor alternated conjugated copolymers, composed of thiophene, bithiophene, thieno[3,2-b]thiophene, and 2,1,3-benzothiadiazole units and differing from each other by the nature and the number of 3-alkylthiophene in the backbone, have been synthesized by Stille cross-coupling polymerization. The material's optical and electrochemical properties, in solution and in thin films, have been investigated using UV-Visible absorption and cyclic voltammetry. Bulk heterojunction solar cells using blends of the newly synthesized copolymers, as electron donor, and C60-PCBM or C70-PCBM, as electron transporting material, have been elaborated. A maximum power conversion efficiency of 1.8% is achieved with a 1:4 PPBzT2-C12:C70-PCBM weight ratio.
Methoxy PEG amine with molecular weight of 5k and [epsiv]-caprolactone with molecular weight of 1 960 were conjugated to a peptide comprising three cysteine residues. The shift of peak molecular weight and narrow molecular weight distribution in GPC trace without any noticeable shoulder as well as 1H NMR analysis confirmed the successful synthesis of the copolymer. A modified O/W dialysis system was employed to prepare self-aggregates having the size around 210 nm. During the dialysis, stabilized aggregates were obtained by intermolecular disulfide bonds via oxidation. Critical aggregate concentration (CAC) of the copolymer was determined as 0.07 mg · mL-1 and disulfide-stabilized self-aggregates remained stable regardless of the concentration without displaying CAC. Doxorubicin-loading amount and efficiency was 8.7 and 26.0%, respectively. Release profile of doxorubicin below CAC at 37 °C showed a sustained release and the addition of D,L-dithiothreitol (DTT) after 24 h triggered a burst release of doxorubicin. Intermolecular disulfide bonds via oxidation stabilized the polymeric aggregates even in the diluted condition similar to that in the bloodstream and addition of DTT destabilized the aggregates to burst encapsulated doxorubicin in the reductive condition.
Ulvan, a sulfated cell-wall polysaccharide extracted from green seaweeds, is functionalized by grafting methacryloyl moieties as a radical polymerizable group and photopolymerized under UV irradiation in order to attain biodegradable hydrogels. The functionalization reaction is carried out by using methacrylic anhydride or glycidyl methacrylate according to two basic procedures applied to polysaccharides. The functionalization of Ulvan is determined by FT-IR and 1H NMR spectroscopy and confirmed by DSC analysis. Hydrogels were characterized by FT-IR and by 1H NMR spectroscopies and their swelling behaviour assessed in terms of degree of swelling using PBS 1 × pH 7.4 as a medium in order to check their stability under physiological conditions.
This review article surveys the electronic and photophysical properties of conjugated organometallic polymers built upon the title compound and its related derivatives focussing primarily on systems investigated in our laboratories. The general structure of the polymers is (trans-bis(para-ethynylbenzene)bis(phosphine)platinum(II)-G)n where G is a conjugated group such as thiophene, fluorene, carbazole, substituted silole, quinone derivative, and metalloporphyrin residue, or a non-conjugated main-group moiety. Systems based on substituted phenylene units and other related fused rings are also discussed. The phosphine ligands are generally triethyl- or tri-n-butylphosphine groups. These trans-platinum(II) polymers and the corresponding model compounds are compared to the corresponding ortho-derivatives in the quinone series, and the newly prepared paracyclophane-containing polymers. For the porphyrin series, a comparison of fully conjugated oligomers exhibiting the general structure (trans-bis(para-ethynyl(zinc(porphyrin)))bis(phosphine)platinum(II))n (i.e., the C6H4 group is absent from the main chain) will be made. This contribution also includes a description of the properties of the mononuclear chromophore itself, properties that define those of the polymers. Potential applications with regard to electronic and optical devices will be highlighted. These soluble and stable materials feature both the processing advantages of polymers and the functionality provided by the presence of metal centers. These multifunctional organometallic polyyne polymers exhibit convenient structural variability as well as optical and electronic properties, which renders them important for use in different research domains as chemical sensors and sensor protectors, as converters for light/electricity signals, and as patternable precursors to magnetic metal alloy nanoparticles.
A novel approach is employed to produce core-corona nanospheres, which introduces a stereoregular hydrophilic part to an amphiphilic block copolymer. The resultant morphology is reported using isotactic-poly(methacrylic acid)-block-poly(butyl acrylate). Infrared spectroscopy revealed a supramolecular interaction, and X ray diffraction revealed the crystallization of the outer isotactic-poly(methacrylic acid) part. The nanostructure, which looks like a nanosized 'grape', was formed when nanospheres and nanofibers coexisted simultaneously and partially fused.
We applied 1,3-dipolar cycloaddition to bind ethynylferrocene onto 6I-azido-6I-deoxycyclomaltoheptaose under microwave assisted conditions. The process was investigated by 1H NMR, FT-IR spectroscopy, and MALDI-TOF mass spectrometry. The ability of the synthesized compound to self-organize to cyclic supramolecular structures was investigated by dynamic light scattering measurements and cryo-transmission electron microscopy.
A new synthesis of amphiphilic biodegradable copolymers consisting of hydrophobic poly(3-hydroxyalkanoate) (PHA) backbone and hydrophilic poly(ethylene glycol) (PEG) units as side chains is described. Poly[(3-hydroxyoctanoate)-co-(3-hydroxyundecenoate)] (PHOU) was first methanolyzed and its unsaturated side chains were quantitatively oxidized to carboxylic acid. Esterification with propargyl alcohol led to an alkyne-containing "clickable" PHA in 71% conversion. Its reactivity was successfully demonstrated by grafting azide-terminated PEG chains of 550 and 5 000 g · mol-1, respectively. All products were fully characterized using GPC, 1H, and COSY NMR.
This study deals with the production of starch microspheres containing insulin using the sonochemical technique. The structure and properties of the final product were studied using SEM, FTIR and XRD. A microsphere size of 600 nm and the size distribution of the starch microspheres with encapsulated insulin were determined. A spectrophotometric analytical procedure was selected to evaluate the amount of loaded insulin in the starch microspheres and to perform the release studies. The product is organized in a double-layer structure (insulin layer covered by starch layer), and this composite may provide a new system for the administration of protein drugs. The microspherilization process involves the degradation of the starch to the smaller fragments due to the application of high-intensity ultrasound, and the organization of these fragments in a microsphere structure using the same type of bonds as in regular starch.
Natural materials, such as bone and spider silk, possess remarkable properties as a result of sophisticated nanoscale structuring. They have inspired the design of synthetic materials whose structure at the nanoscale is carefully engineered or where nanoparticles, such as rods or wires, are self-assembled. Although much work has been done in recent years to create ordered structures using diblock copolymers and template-assisted assembly, no reports describe highly ordered, three-dimensional nanotube arrays within a polymeric material. There are only reports of two-dimensional network structures and structures on micrometer-size scales. Here, we describe an approach that uses plasticized colloidal particles as a template for the self-assembly of carbon nanotubes (CNTs) into ordered, three-dimensional networks. The nanocomposites can be strained by over 200% and still retain high conductivity when relaxed. The method is potentially general and so may find applications in areas such as sensing, photonics, and functional composites.
Copolymerization of ethylene with 5-norbornene-2-methanol and terpolymerization of ethylene with norbornene and 5-norbornene-2-methanol by a rare-earth metal based catalyst, specifically the half-sandwich bis(alkyl) scandium precursor [Sc([eta]5-C5Me4SiMe3)([eta]1-CH2SiMe3)2(THF)] activated by [Ph3C][B(C6F5)4] were successfully achieved for the first time. A protocol for masking of [bond]OH functionality by AliBu3 to avoid catalyst poisoning was exploited. Copolymers with high molar masses and noticeable incorporation of functionalized norbornene derivative were obtained. Terpolymers with very high molar masses and with a broad range of composition were prepared with excellent yields.
Three accessible azobenzene mesogen-substituted diacetylene monomers (DA1, DA2, and DA3) were synthesized and the effect of the molecular structure on the photopolymerization behavior and self-assembled structures of the resulting azobenzene-substituted polydiacetylene (PDA) films had been investigated in detail. The films derived from DA1 were substantially polymerized into blue phase. However, the films derived from DA2 and DA3 were polymerized into red phase directly. The morphology, packing structure, and thermal stability of the resulting azobenzene-substituted PDA films were characterized in detail by SEM, XRD as well as POM measurements. PDA1 formed micrometer-sized lamellar crystal structures, while PDA2 and PDA3 both formed spherulitic crystal structures. The strong [pi]-[pi] stacking interaction among side chains was essential for maintaining high stability upon thermal stimulus.
We present a new type of nanoporous hydroquinone/catechol formaldehyde resin synthesized by a one-pot route, with a surface area of up to 1 112 m2 · g-1. The resins show highly efficient reactive adsorption for silver/gold (silver adsorbance up to 2.43 g · g-1) and excellent selectivity for gold (Kd is as high as 1 914 090 mL · g-1). The first-used resins can be regenerated with NaHSO3, and the gold capacities of the recycled PCFR and PHFR reach 44 and 78% of their first loading capacities, respectively.
This contribution explores different strategies for the synthesis of side chain functional polydepsipeptides. First, the ring-opening polymerization of side chain functional morpholine-2,5-diones is revisited and the optimized reaction conditions used for the polymerization of (Z)-L-Lys, (Boc)-L-Lys and L-allylglycine based morpholine-2,5-diones. As a first approach towards side chain functional polydepsipeptides, the deprotection of poly(Glc-alt-(Z)-L-Lys) and poly(Glc-alt-(Boc)-L-Lys) is evaluated. Although under appropriate conditions, the side chain protecting groups can be quantitatively removed, the reaction conditions used here were found to lead to backbone degradation. As an alternative approach, the thiol-ene post-polymerization modification of poly(Glc-alt-allylglycine) is explored. Free radical addition of various [omega]-functional thiols was found to proceed without backbone degradation and in several cases with quantitative allyl group conversion. The post-polymerization modification strategy is attractive as it obviates the need for protecting group chemistry and facilitates the synthesis of diverse libraries of side chain functional polydepsipeptides.
A series of polythiophene derivatives P1-P5 containing carbazole side chains were designed and synthesized via the Stille polymerization. All carbazole containing polymers showed broad absorption in the visible region. The power conversion efficiencies of solar cells based on blends of two component copolymers and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) were determined to be 0.29 and 0.56% for P1 and P5, respectively. For solar cells fabricated with the three component copolymers and PC61BM, the efficiencies were 0.56% for P2, 0.86% for P3, and 0.70% for P4. The introduction of electron-donating carbazole side chains can broaden the absorption in the visible region and meanwhile reduce phase separation due to the steric hinderance of the carbazole moiety to the conjugated main chain. Improving efficiency needs a balance of broad absorption and ordered packing of polymer chains in the solid state.
The possibility of introducing hydrolytically cleavable ester linkages onto the poly(N,N-dimethylaminoethyl methacrylate) for the formation of less toxic and degradable polycations is shown in this work. For achieving this aim, the copolymerization behavior of 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), with N,N-dimethylaminoethyl methacrylate (DMAEMA) is studied by free radical ring-opening polymerization. Structural characterization is performed using 1D and 2D NMR techniques. Under optimized reaction conditions, quantitative ring-opening of BMDO took place during the copolymerizations leading to the formation of poly(DMAEMA-co-ester)s. Blocky random copolymers were further quaternized by alkyl bromide to generate degradable cation containing polymers. Cytotoxicity results were highly encouraging and showed less cytotoxicity as compared to polyethyleneimine, which was used as a positive control. The formation and characterization of highly stable copolymer/DNA polyplexes is also shown here.
The synthesis of novel linear-hyperbranched (linhb) polyether block copolymers based on poly(ethylene oxide) and branched poly(glycerol), bearing a single pyrene or myristyl moiety at the [alpha]-position of the linear chain is described. The polymers exhibit low polydispersity ( < 1.3) and controlled molecular weights ( = 5 000 g · mol-1). The mainly hydrophilic block copolymers with multiple hydroxyl end groups readily dissolve multiwalled carbon nanotubes (MWCNTs) in water by mixing and subsequent sonification, resulting in noncovalent attachment of the linhb hybrid structure to the carbon nanotubes (CNTs). Transmission electron microscopy (TEM) was employed to visualize the solubilized nanotubes; after sulfation of the multiple hydroxyl groups the polymer layer was detected in the TEM images.
Soybean oil is one of the most promising renewable raw materials for polymers. Cationic copolymerization with a variety of olefinic monomers gives interesting materials but the curing process is tedious and high temperatures and long reaction times are needed. We studied the cationic homopolymerization of soybean oil and its copolymerization with styrene and divinylbenzene under microwave irradiation using boron trifluoride etherate as initiator and the comparison with conventional heating showed a great enhancement in reaction rates.
A novel dispersion polymerization system to produce "clean" polystyrene (PS) particles, using a polymerizable sodium styrene sulfonate (NaSS) as stabilizer, and a mixture of methanol/water (MeOH/H2O) as the reaction medium was investigated. The effects of the polymerization parameters, such as the methanol/water ratio in the medium, the concentration of the stabilizer, the initiator and the monomer on the resulting particles were studied. By observing the morphological changes of the PS particles by SEM and analyzing the surface chemical composition of these particles by XPS, it is found that this system had the following unique features: as little as 0.05 wt.-% of NaSS (based on styrene as opposed to 5 wt.-% for a routine dispersion polymerization system) was enough to prepare stable latex with monodisperse particles; as high as 20 vol.-% of monomer (as opposed to 5 wt.-% for polymerization system in the absence of surfactants) could be added into the polymerization system to produce monodisperse particles; surface-charged and monodisperse particles with average diameters of approximately 470-1600 nm could be directly obtained.
A series of functional initiators for atom transfer radical polymerization (ATRP) was prepared. These structures contain an ATRP initiating site, a labile p-alkoxybenzyl ester Wang linker and a functional end-group (i.e., [bond]COOH, [bond]N3, [bond]OH, [bond]C[triple bond]CH, or [bond]NHFmoc). These novel initiators can be utilized for synthesizing well-defined soluble polymer supports. For instance, the azide-, alcohol-, alkyne-, and NHFmoc- derivatives were tested as initiators for the bulk ATRP of styrene. SEC, MALDI-TOF-MS, and NMR measurements indicated that well-defined polystyrene samples with defined end-groups have been synthesized in this process. Moreover, it was demonstrated that the labile Wang linkers could be easily cleaved with a mild trifluoroacetic acid treatment.
In this paper, we describe the thiol-ene "click" reaction with modified poly methacrylic acid in water. The thiol group was implemented by a polymer analogous condensation reaction of polymethacrylic acid (1) and cysteamine (2), which was carried out in bulk by use of microwave. The allyl modified polymethacrylic acid (5) was obtained by DCC-coupling of the allyl amine onto the polymethacrylic acid backbone. By combination of cysteamine (3) and allyl modified polymethacrylic acid (5) the thiol-ene click reaction could be started with a redox initiator in aqueous solution at room temperature. The kinetics of this reaction were determined by 1H NMR spectroscopy and the resulting hydrogels were analyzed by rheological measurements and differential scanning calorimetry (DSC).
A novel amphiphilic diblock copolymer composed of a hydrophilic poly(ethylene oxide) block and a hydrophobic block copolymerized by azobenzene-containing methacrylate and N-isopropylacrylamide was synthesized using ATRP. The polymer micelles showed dual responsiveness to heat and light. The size of the micelles was dependent on temperature and the encapsulated substance in the hydrophobic cores was released during heating and cooling processes. The hydrophobicity of the micellar cores appeared as a reversible change in response to light with neither disruption of the micelles nor leakage of the encapsulated substance while H-aggregation of the azobenzene moieties was detected.
Poly(dimethylsiloxane) copolymers were synthesized directly from AA/BB monomers employing a CuAAC reaction (click chemistry) in a polyaddition approach. Using organic dialkynes and oligo(siloxane)s end-functionalized with azide moieties it was possible to obtain siloxane-based copolymers with TPE properties by click chemistry for the first time. As seen from DSC experiments, properties were strongly dependent on the incorporated organic comonomer.
A simple and efficient Diels-Alder (DA) reaction on carbon material has been demonstrated. The present work involves single and multiwall carbon nanotubes (CNTs), as well as Herringbone carbon nanofiber. The CNTs show a dual nature of reactivity in DA reaction, i.e., they behave both as dienophile and diene with furfuryl groups and maleic anhydride derivatives, respectively. Various functional groups, including alcohol, amine, epoxy, carboxylic and ester, have been introduced on the carbon materials. The results suggest that the reactivity of CNT in DA reaction may resemble the chemistry of small molecules.
A photocurable polymer mixture made of poly(ethylene glycol) (PEG) dimethacrylate and monomethacrylate is proposed as structural material for the fabrication and easy prototyping of the microfluidics for Lab-on-Chip (LOC) devices. The kinetics of photopolymerisation and some material properties such as its viscoelastic behaviour (by dynamic-mechanical analysis) and surface wettability (by contact angle) were studied. The PCR biocompatibility of the PEG crosslinked material was favourably assessed by preliminary in vitro tests. A direct fabrication method of controlled geometry microchannels is finally presented by direct photopolymerisation under UV light irradiation through photomasks without the need of a master. Finally the same process was successfully used to assembly and seal the microchannels.
The effects of temperature and solvent on the [beta]-phase formation and energy transfer in an Ir(III) complex-containing polyfluorene were investigated. Efficient energy transfer from polyfluorenes host to Ir complexes guest can be realized at low temperature. The formation of [beta]-phase was observed both in THF solution at low temperature and as suspended nano-particles at room temperature. In addition, phosphorescent polymer nanoparticles were prepared successfully and exhibited efficient phosphorescent emission.
Here, we describe a procedure to manufacture smart hybrid probes that exhibit tunable optical properties as a function of multiple environmental variations. Initially, we achieved a one-pot synthesis of gold-PREP (photo-responsive elastin-like polymer) conjugate Gold-AzoGlu15 via reduction of auric acid in the presence of PREP AzoGlu15. Outstandingly, Gold-AzoGlu15 exhibited pH and temperature sensitiveness. However, Gold-AzoGlu15 was not UV-vis sensitive. We noticed that photo-isomerisation of azobenzene moieties in Gold-AzoGlu15 could not be detected by UV-vis spectroscopy. In a subsequent step, we explored the use of cyclodextrins and the formation of alkanethiol mixed-monolayers over mother Gold-AzoGlu15 by thiol-place exchange reactions in order to decouple photo-isomerisation of azobenzene from the bulk phase absorption. In this sense we achieved the synthesis of [beta]-cyclodextrin capped Gold-CD-AzoGlu15. Notable was that cis-trans photo-conversion of azobenzene groups in Gold-CD-AzoGlu15 could be successfully detected. Finally, we present the optical properties exhibited by multi-sensitive probe Gold-CD-AzoGlu15 as a function of pH, temperature and UV-vis irradiation. We think that gold-PREP hybrids could be of great interest in the design of multi-functional chromophore-metal nanocomposites that operate in aqueous media for the development of multi-stimuli sensitive detectors for biosensing applications.
We reveal that a beam of low-energy electrons (18 eV) can directly trigger long-range molecular ordering of an amorphous, semi-flexible oligomer in a few minutes without the prerequisite of pre-orientation. A strong endothermic transition was detected with a micro-thermal analyzer on the areas that had been exposed to the electron irradiation while the areas that were shielded from the irradiation by a protective mask remained amorphous as usual. This result suggests that long-range molecular ordering only develops in the area of the oligomer film under electron irradiation. This is the first-time effort to use electron irradiation to control the long-range ordering of an amorphous organic thin film above the glass transition temperature.
Here, we report the first results of investigation the local structure and photoactive properties of iron-containing dendromesogens based on decyloxybenzoate substituted poly(propylene imine) dendrimers of the first to fifth generations. Iron ions existing in a high-spin state are coordinated in dendrimer ligands by two kinds of iron-complexing sites with an octahedral and a tetrahedral symmetry. Octahedral (high-symmetry) centers are located at the border of the dendrimeric core, while the tetrahedral centers with strong rhombic distortion of iron environment are distributed throughout all branching of the dendrimeric core. It has been found that all iron-containing dendromesogens exhibit light-harvesting and fluorescence properties.
One of the most challenging issues remaining in the design and the synthesis of robust nanostructured polymers blends is incorporating long crystallizable chains while preserving the co-continuity of the phases. Here, we demonstrate that by reactive blending of functionalized polyolefin and polyamides such co-continuous structures can be obtained provided that a bimodal mixture of short and long polyamides is used. The short chains react more readily to form graft copolymers that facilitate both grafting of long chains and formation of nanostructures. We discuss different mixing strategies, characterize, and compare reacted products and resulting blend structures.
We synthesized an alternating copolymer of N-allylmaleimide (AMI) and isobutene (IB) [poly(AMI-alt-IB)] as a new class of thermosetting polymers by the free radical copolymerization process. The reactivity of the maleimide group of the AMI monomer was evaluated to be 103 times higher than that of the N-allyl group based on the results for the ternary copolymerization system composed of N-methylmaleimide (MMI), N-allylphthalimide (AP), and IB. The maleimide moiety exclusively participated in the propagation during the copolymerization of AMI with IB, resulting in the formation of the soluble poly(AMI-alt-IB). The copolymer included an alternating repeating structure consisting of maleimide and IB units in the main chain and the unreacted allyl group in the side chain. The onset temperature of the decomposition for poly(AMI-alt-IB) was over 400 °C in a nitrogen stream. The transparent cast film of poly(AMI-alt-IB) was readily cured upon heating without any catalyst.
Four poly(N,N-dimethylacrylamide)-block-poly(L-lysine) (PDMAM-block-PLL) hybrid diblock copolymers and two PLL homo-polypeptides are prepared via ROP of [epsiv]-trifluoroacetyl-L-lysine N-carboxyanhydride initiated by primary amino-terminated PDMAM and n-hexylamine respectively. The PLL blocks render the copolymers a multi-responsive behavior in aqueous solution due to their conformational transitions from random coil to [alpha]-helix with increasing pH, and from [alpha]-helix to [beta]-sheet upon heating. The random coil-to-[alpha]-helix transition is found to depend on the PLL length: the longer the peptide segment, the more readily the transition occurred. The same trend was observed for the [alpha]-helix-to-[beta]-sheet transition, which was found to be inhibited for short polypeptides unless conjugated with the PDMAM block.
The stabilisation of miniemulsions using an in situ generated surfactant is presented. This surfactant, prepared from of a water-soluble base and an oil-soluble long chain acid was successfully used to create stable miniemulsions with up to 60 vol.-% organic phase. It is shown that the creation of a surface active species at the oil-water interface allowed stable miniemulsions to be generated more rapidly than when using conventional surfactant. In addition, polymerised miniemulsions exhibited less secondary nucleation when in situ surfactants were used.
Today, high-ordered micro- and nano-patterned surfaces are widely used in many areas, such as in the preparation of super-thin dielectric films, photonic crystals, antireflective films, super-non-wetting surfaces, bio-compatible surfaces and microelectric devices. Considering the critical fabrication conditions and the irreducible high cost of the photolithography technique in patterning nano-scale structures (<100 nm), the development of other micro- and nano-patterning techniques that can be used to fabricate long-range ordered features - especially nanoscale arrays - is a promising subject in surface science. In contrast to the traditional photolithography patterning technique, block copolymers can spontaneously phase separate into arrays of periodic patterns with length-scales of 10-50 nm, which provides an efficient pathway to pattern nanoscale features. Today, preparing long-range ordered arrays by block copolymer microphase separation is one of the most promising techniques for the fabrication of nanoscale arrays, not only being a simple process but also having a lower cost than traditional methods. In this feature article, we first summarize the many techniques developed to induce ordering in the microphase separation of the block copolymer thin films. Then, evolution, order-order transitions and reversible switching microdomains are considered, since they are very important in the ordered engineering of microphase separation of the block copolymer thin films. Finally, the outlook of this research area will be given.
New amphiphilic block copolymers consisting of N-vinyl pyrrolidone and vinyl acetate were synthesized via controlled radical polymerization using a reversible addition/fragmentation chain transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) system. The synthesis was carried out in 1,4-dioxane as process solvent. In order to get conclusions on the mechanism of the polymerization the molecular structure of formed copolymers was analysed by means of different analytical techniques. 13C NMR spectroscopy was used for the determination of the monomer ratios. End groups were analysed by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This technique was also used to determine possible fragmentations of the RAFT end groups. By means of a combination of size exclusion chromatography, 13C NMR and static light scattering molar mass distributions and absolute molar masses could be analysed. The results clearly show a non-ideal RAFT mechanism.
Graft copolyesters with a PCL backbone and PLLA side chains were successfully prepared in three steps avoiding transesterification. First [epsiv]-caprolactone was polymerised with 1,6-hexane diol as initiator to obtain hydroxytelechelic oligo([epsiv]-caprolactone)s. These diols were then subjected - in the second step - to polycondensation with L-malic acid yielding in linear poly[oligo([epsiv]-caprolactone)L-malate] having secondary hydroxyl functions in the side chain. For both reactions scandium triflate Sc(OTf)3 was used as a catalyst. In the third step various amounts of L-lactide were grafted from the polymer backbone using Zn(oct)2 as catalyst. The successful reaction was confirmed by NMR and SEC (size exclusion chromatography) analysis. Further the thermal properties of the graft copolymers with different graft lengths were determined via differential scanning calorimetry.
The layer-by-layer (LBL) assembly of poly(diallyldimethylammonium chloride) and poly(sodium styrene sulfonate) on poly(sulfo propyl methacrylate) brushes resulted in films with nanometer- and micrometer-sized holes and ledges, observed by atomic force microscopy and scanning electron microscopy. Polyelectrolyte assembly was followed by the quartz microbalance technique. The formation of ledges and holes is explained by the interaction of the brush polymers with the incoming polyelectrolytes during the LBL assembly, inducing a spatially localized and self-organized accumulation of the assembled polymers.
Poly(2-alkyl-2-oxazoline)s can be regarded as pseudo-peptides or bioinspired polymers, which are available through living/controlled cationic polymerization and polymer ("click") modification procedures. Materials and solution properties may be adjusted via the nature of the side chain (hydrophilic-hydrophobic, chiral, bio-functional, etc.), opening the way to stimulus-responsive materials and complex colloidal structures in aqueous environments. Herein, we give an overview over the macromolecular engineering of polyoxazolines, including the synthesis of biohybrids, and the "smart"/bioinspired aggregation behavior in solution.
Highly functional and monodisperse macromolecules with tailored architecture constitute the key to designing efficient and smart nanomaterials. Dendrimers offer real potential to achieve this goal, and one of the earlier challenges faced by this novel class of polymers has been addressed by the evolution of synthetic methodologies. This review provides an evaluation of the role played by chemistry in taking these macromolecules of academic relevance to practical industrial and biological applications, in a relatively short period. One can now construct dendrimers in a 'made-to-order' fashion, for numerous applications in a variety of disciplines.
Crystallization-induced vertical stratified structures were constructed based on double-crystalline poly(3-hexylthiophene) (P3HT)/poly(ethylene glycol)s (PEG) systems at room temperature, in which the P3HT crystallinity and the mechanism were investigated. Vertical stratified microstructures with highly crystalline P3HT network on the surface were formed when depositing from marginal solvents, while lateral phase-separated structures or low P3HT crystallinity were observed for good solvents. The morphological differences came from the solvent effect. In marginal solvents, p-xylene and dichloromethane, P3HT large-scale microcrystallites were generated in solution, which ensured the priority of P3HT crystalline sequence, and phase separation began in the liquid states. When the PEG matrix began to crystallize, great energy from which the second phase separation was induced drove P3HT crystallites to the surface, resulting in the formation of vertical stratified microstructures with highly crystalline P3HT network on the surface. The method, crystallization-induced phase segregation of crystalline-crystalline blends in marginal solvent, provides a facile way to construct vertically stratified structures, in which P3HT highly crystalline network is favored.
A set of poly(propylene) composites containing different amounts of copper nanoparticles (CNP) were prepared by the melt mixed method and their antimicrobial behavior was quantitatively studied. The time needed to reduce the bacteria to 50% dropped to half with only 1 v/v % of CNP, compared to the polymer without CNP. After 4 h, this composite killed more than 99.9% of the bacteria. The biocide kinetics can be controlled by the nanofiller content; composites with CNP concentrations higher than 10 v/v % eliminated 99% of the bacteria in less than 2 h. X-ray photoelectron spectroscopy did not detect CNP at the surface, therefore the biocide behavior was attributed to copper in the bulk of the composite.
Silver nanoparticles have been used for a long time and recently various methods have been additionally developed for their production. Here we report for the first time a solid-state high-speed vibration milling method for the synthesis of silver nanoparticles, in which poly(vinylpyrrolidone) is used for the reduction of the silver salt. The synthesis is performed at room temperature and no surfactant to direct the anisotropic growth of the nanoparticles is required. The formation of the nanoparticles was studied by UV-Visible spectroscopy, transmission electron microscopy, and powder X-ray diffraction techniques. The nanoparticles synthesized were found to be uniform in size and shape with an average diameter of less than 5 nm. In addition, the antimicrobial activity of these silver nanoparticles was investigated against Escherichia coli and found to be positive.
Thin hydrogel films of the thermoresponsive polymer poly(N-isopropylacrylamide) (pNIPAm) were prepared by electrochemically triggered reversible addition-fragmentation chain transfer (RAFT) polymerization. Two different RAFT agents were employed, which work in either acidic or basic solution. In both cases, addition of RAFT agents had an influence on the thickness and the surface morphology of the films. At low concentration, the polymerization efficiency increased. At high concentration, the efficiency decreased at acidic pH, while it remained constant under basic conditions. Neither RAFT agent displayed electrochemical activity on its own, but they did modify the electrochemical behavior of the initiator. The addition of RAFT agent strongly enhances the homogeneity of the hydrogel surfaces, which presumably is due to a reduced amount of microgel formation.
An important category of self-healing materials relies on the release of a healing agent from a capsule upon the occurrence of damage to the material. Visualization of the release of the healing agent is difficult to accomplish. Here we show that a profluorophore can successfully be used to visualize the local release of a healing agent in a self-healing coating. A tetra-functional thiol compound encapsulated in nanocapsules or microcapsules is dispersed in a poly(methyl acrylate) film, in which the profluorophore is molecularly dispersed. A strong fluorescence signal is observed when a cut is introduced in the film. This fluorescence provides clear evidence that the capsules rupture locally during the introduction of a cut. In a more general sense, it proves that profluorophores can be very useful in materials science.
Solid-state complexation of syndiotactic polystyrene (sPS) with a crown ether compound, 1,4,7,10-tetraoxa-cyclododecane (12-crown-4), took place when a film of sPS/chloroform clathrate was subjected to a guest exchange procedure assisted with a plasticizing agent. The new guest 12-crown-4 molecules were incorporated into the crystalline region of the sPS film, without causing a large conformational change of host sPS helices. X-ray diffraction and thermogravimetric investigations showed that sPS/12-crown-4 complex had a clathrate complex structure which contained four 12-crown-4 molecules per unit cell. IR and Raman data suggested that 12-crown-4 took a Ci-type conformation in the sPS complex phase.
A one-step method to fabricate a biomimetic dual-scale hierarchical structure for a transparent anti-reflective, self-cleaning layer for organic solar cells is reported. Template-mediated UV replica molding is used to directly create a multi-functional surface with an acrylate-functionalized perfluoropolyether without complicated processing steps. The surface exhibits superhydrophobic properties and self-cleaning characteristics. In addition, the surface leads to an enhancement of photovoltaic power conversion efficiency by [ap]10% as a result of reflection suppression and transmittance enhancement. The method can easily be applied to large area substrates (22 cm × 24 cm) in a cost-effective manner. Furthermore, the solar cell can withstand harsh outdoor conditions for a long time, without a notable change in the device performance, owing to robust surface layer and non-fouling properties.
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