Fluorescent Nanoparticles through Self‐Assembly of Linear Ionenes and Pyrenetetrasulfonate

We investigated the association of linear cationic model polyelectrolytes with oppositely charged pyrenetetrasulfonate in aqueous solution. Water soluble ionenes were prepared via Menschutkin reaction from 1‐4‐diazabicyclo[2.2.2]octane (DABCO) and dibromoalkenes. UV? Vis results revealed that PY molecules bind to ionenes in a cooperative process due to π–π interaction. Size and structure of the particles vary in dependence of inter‐charge distance on the ionene backbone. Stable spherical dye–ionene assemblies with radii between 50 and 200 nm have been obtained with one polyelectrolyte (PD4), while this was not possible with a different polyelectrolyte (PD6) or in either case at polyelectrolyte excess. It was possible to deposit the fluorescent polyelectrolyte–dye aggregates onto mica surfaces.

     

Preparation and Characterization of Acetoacetoxyethyl Methacrylate‐Based Gels

Novel polymeric gels have been prepared by radical copolymerization of acetoacetoxyethyl methacrylate (AAEM) and hydroxyethyl methacrylate (HEMA) in water‐ethanol medium. The influence of the HEMA:AAEM ratio and crosslinker concentration on properties of gels was studied. Independently on gel composition the maximum swelling was detected in chloroform. It was found that PAAEM gels possess phase transition temperature or upper critical solution temperature (UCST) in alcohol‐water solutions. UCST decreases in linear order from 75 to 10 °C when HEMA content in gel structure increases. The minimal UCST of AAEM/HEMA gels in binary alcohol‐water mixtures is shifted toward lower temperatures and lower alcohol concentrations when the alkyl chain of alcohol increases.

AAEM/HEMA gels prepared at different BIS concentrations (1:1 mol‐%, 2:2.5 mol‐%, 3:5 mol‐%).     

Gas‐Phase Assisted Surface Polymerization of Vinyl Monomers with Fe‐Based Initiating Systems

Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl₂/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.

GASP schemes with a simple initiating system Fe(0)/MBPA.     

Poly(acrylamide‐co‐itaconic acid) and Semi‐IPNS with Poly(ethylene glycol): Preparation and Characterization

Summary: A pH‐responsive poly(acrylamide‐co‐itaconic acid) (PAAm/IA) hydrogel and semi‐interpenetrating networks (semi‐IPNs) with 5, 10 and 15 wt.‐% of poly(ethylene glycol) (PAAm/IA/PEG), were synthesized. Their swelling behavior was studied in the pH range from 1.76 to 7.81, as well as their oscillatory swelling behavior at pH = 7.81 and pH = 1.7. Throughout these studies, the gels maintained their mechanical strengths and shape. The shear storage (G′) and loss (G″) moduli, obtained as a function of frequency, for the gels as formed and at equilibrium swelling were higher for the semi‐IPNs than for the copolymer hydrogel. The shear storage moduli of copolymer hydrogel and semi‐IPNs as formed were independent of frequency over the whole experimental range, whereas the values for the gels at equilibrium swelling decreased with increasing degree of swelling, i.e., the PAAm/IA hydrogel which exhibited the largest swelling had the lowest G′ value. The G′ and G″ values also depended on the content of PEG.

Diffusion exponent vs. pH for PAAm, copolymer hydrogel PAAm/IA and semi‐IPN with PEG.     

Evaluation of the Isoconversional Approach to Estimating the Hoffman‐Lauritzen Parameters from the Overall Rates of Non‐Isothermal Crystallization of Polymers

Summary: The isoconversional approach proposed by Vyazovkin for evaluating the Hoffman‐Lauritzen parameters from overall rates of non‐isothermal crystallization was critically applied to two new and fast crystallizing polymers, poly(propylene terephthalate) and poly(butylene naphthalate), which are used for the production of fibers. Non‐isothermal crystallization data were corrected for the effect of the thermal lag and the effective activation energy as a function of temperature was calculated using the method of Friedman. The estimated Hoffman‐Lauritzen parameters, U* and K_g, were consistent with corresponding values from isothermal crystallization experiments obtained either from DSC measurements or using polarized optical microscopy (POM). It was found that the proposed method could simulate the experimental data very well, and the temperature interval under consideration did not allow the detection of any critical breakpoints denoting regime transitions.

Dependence of the effective activation energy on average temperature for PPT.     

Meshless Modeling of pH‐Sensitive Hydrogels Subjected to Coupled pH and Electric Field Stimuli: Young Modulus Effects and Case Studies

The effect of Young's modulus on the behavior of pH‐sensitive hydrogels is studied when subjected to coupled stimuli of solution pH and externally applied electric field. The study is the first instance for coupled stimuli numerical analysis of the hydrogels, in which a multieffect‐coupling pH‐stimulus (MECpH) model is presented. The model considers ionic diffusion, electric potential, and large mechanical deformation. A correlation between diffusive hydrogen ion and charge groups fixed onto the hydrogel polymeric chains by the Langmuir absorption isotherm is incorporated into the model. To validate the model, the computed results by the meshless Hermite‐Cloud technique are compared well with experimental data available from the literature. Then several case studies are conducted for the swelling hydrogel immersed in buffered solution subject to applied electric voltage, especially for the Young modulus effects on the volume variations of the hydrogels.

     

Novel Alternating Dioctyloxyphenylene Vinylene‐Benzothiadiazole Copolymer: Synthesis and Photovoltaic Performance

Summary: A novel alternating conjugated copolymer (poly[(dioctyloxyphenylene vinylene)‐alt‐(2,1,3‐benzothiadiazole)], C8‐PPV‐BT) consisting of electron‐rich dioctyloxybenzene and electron‐deficient 2,1,3‐benzothiadiazole repeat units was synthesized via a Pd‐catalyzed Heck cross‐coupling polycondensation. The thermal, electrochemical, optical properties, and photophysics of C8‐PPV‐BT blended with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) have been investigated. Photovoltaic devices of ITO/PEDOT‐PSS/C8‐PPV‐BT + PCBM (1/4, w/w)/Ba/Al were fabricated and their photovoltaic parameters were measured. The results showed the energy conversion efficiency (η_e) and external quantum efficiency (EQE) were 0.335 and 11.7% (451 nm), respectively, under simulated solar light illumination having light intensity of 78.2 mW · (cm²)^?1 (AM1.5), which were both higher than those of devices based on poly[(dioctyloxyphenylene ethynylene)‐alt‐(2,1,3‐benzothiadiazole)] (C8‐PPE‐BT) and PCBM blend under the same conditions. Optical, electrochemical, and photovoltaic properties of C8‐PPV‐BT and C8‐PPE‐BT copolymers were also compared and discussed.

     

Synthesis and Photovoltaic Properties of Side‐Chain Liquid‐Crystal Click Polymers for Dye‐Sensitized Solar‐Cells Application

SCLCPs are synthesized using “click chemistry”. The resulting polymers, P1 and P2, have good solubilities and molecular‐weight distributions. Their and polydispersities are in the ranges of 26.7–8.4 × 10³ g · mol^?1 and 1.99–1.29, respectively. DSC and POM studies reveal that both polymers exhibit liquid‐crystalline behavior. P1 and P2 are found to display blue emission. DSSCs are fabricated using P1 and P2 as matrices for electrolytes. The maximum PCE of the P1‐ and P2‐based polymer electrolytes is 4.11% (at 1 sun). This synthesis route has again proven to be a useful synthetic methodology for fabricating SCLCPs that are promising materials for device applications.

     

A Study of Copolymerization of 1‐Hexene with 2,5‐Norbornadiene Using Metallocene Catalysts

Summary: Copolymerization of 1‐hexene with a symmetrical diene, namely 2,5‐norbornadiene was studied using four different metallocene catalysts. Copolymerization was found to occur exclusively through one of the two equally reactive endocyclic double bonds with all the four catalysts. Copolymerization results in low molecular weight oligomers with the number average molecular weight ( ) varying from 1 000–3 000. End group analysis of the co‐oligomers revealed that the β‐hydrogen transfer after 2,1 insertion also occurs in the presence of highly regiospecific catalysts. The regio errors were also found to depend on various reaction parameters such as polymerization time, Al/Zr mol ratio, metallocene concentration and polymerization temperature.

Plots of variation in end groups and NBD incorporation with time.     

Block‐Selective Solvent Influence on Morphology of the Micelles Self‐Assembled by PS38‐b‐P(AA190‐co‐MA20)

Summary: The influence of block‐selective solvent on the self‐assembly of polystyrene‐block‐poly[(acrylic acid)‐co‐(methyl acrylate)] was studied. The nature of the block‐selective solvent, which is a binary solvent mixture with different composition, exerts remarkable influence on the morphology of the resulting micelles. When the block‐selective solvent is a binary solvent mixture of acetone and water with acetone content ranging from 0 to 90 vol.‐%, the resulting aggregates are core‐shell spheres with diameter about 60 nm, porous aggregates with diameter of 100, 180 and 250 nm, and core‐shell cauliflower‐like aggregates with size about 200 nm, respectively. The reason that the morphology of resulting micelles changes with acetone content has been discussed. The structure of the resulting micelles is further characterized in detail by DLS and SLS. Morphological tuning is also achieved by using a binary solvent mixture of ethanol and water or a binary solvent mixture of DMF and water as block‐selective solvent. In these cases, core‐shell spheres, hollow aggregates, and incompact aggregates are formed with the ethanol or DMF concentration ranging from 10 to 80 vol.‐%.

     

Dansyl Fluorescence and Local Structure of Dansyl‐Labeled Core‐Shell and Core‐Hair Type Microspheres in Solution

Core‐shell type microspheres with fluorescent dansyl groups at random sites in crosslinked poly(N‐isopropylacrylamide) (PNIPAM) shell chains and core‐hair type microspheres with dansyl groups at terminal sites of PNIPAM hair chains graft‐polymerized with living‐radical mechanism were prepared. Fluorescent spectra indicating the microenvironments of dansyl groups attached to the microspheres and their dependences on temperature and solvent compositions were compared to those of dansyl groups in PNIPAM bulk gels and in free solutions. Fluorescence peak wavelength of dansyl groups in the core‐shell type microspheres showed an extraordinary blue shift in water, suggesting that dansyl groups are incorporated in the semi‐interpenetrating polymer network (SIPN) region of the core‐shell boundary. This is supported by a confocal laser‐scanning fluorescence microscope (CLFM) image of a single particle for the core‐shell type microsphere. Dansyl groups at the chain ends of PNIPAN hairs of the core‐hair type microspheres in water are also located on the surface of hydrophobic cores.

     

Noncovalent Nonspecific Functionalization and Solubilization of Multi‐Walled Carbon Nanotubes at High Concentrations with a Hyperbranched Polyethylene

A hyperbranched polyethylene (HBPE) is employed herein for noncovalent nonspecific functionalization and solubilization of multi‐walled carbon nanotubes (MWCNTs) in organic solvents. Though constructed solely from ethylene without any specific functionality, this unique hyperbranched polymer has been found to effectively solubilize MWCNTs at surprisingly high concentrations (up to 1 235 mg · L^?1) in organic solvents such as chloroform and THF. These solubilities are comparable to and even better than the reported best values obtained through noncovalent specific functionalization with conjugated polymers capable of forming specific π‐π interaction with nanotubes in organic solvents. TEM and XRD results confirm that the nanotubes are completely exfoliated and debundled/de‐entangled upon functionalization with HBPE.

     

pH‐Sensitive Micelles Formed by Interchain Hydrogen Bonding of Poly(methacrylic acid)‐block‐Poly(ethylene oxide) Copolymers

pH‐sensitive micelles formed by interchain hydrogen bonding of poly(methacrylic acid)‐block‐poly(ethylene oxide) copolymers were prepared and investigated at pH < 5. Both and R_h of the micelles increase with decreasing pH of the solution, displaying an asymptotic tendency at low pH values. The observed micelles are well‐defined nanoparticles with narrow size distributions (polydispersity ΔR_h/R_h ≤ 0.05) comparable with regular diblock copolymer micelles. The CMCs occur slightly below c = 1 × 10^?4 g · mL^?1. The micelles are negatively charged and their time stability is lower than that of regular copolymer micelles based purely on hydrophobic interactions.

     

Cylindrical Polypeptide Brushes

Summary: Cylindrical brushes with poly(L ‐lysine) and poly(L ‐glutamate) side chains were prepared by “grafting through” and “grafting from” techniques. Grafting from is shown to be more successful for the synthesis of cylindrical brushes with high molar mass main and side chains.

AFM height image of polypeptide brushes with protected polylysine side chains spin‐cast from HFIP solution.     

Light‐Tunable Thermosensitivity of Polymer‐Coated Gold Nanoparticles Achieved by Light‐Controlled Molecular Recognition

Thermo‐ and photosensitive gold nanoparticles (AuNPs) coated with an azobenzene‐contained P(DMA‐PAPA‐MAEL) copolymer are prepared by ligand exchange reactions. The photoisomerization of azobenzene moiety on the surface of P(DMA‐PAPA‐MAEL)‐coated AuNPs is detected by means of UV‐Vis spectroscopy with the presence or absence of free α‐cyclodextrin. When subjected to visible and UV light irradiation alternately, P(DMA‐PAPA‐MAEL)‐coated AuNPs in the presence of free α‐CD display a light‐tunable lower critical solution temperature through light‐controlled molecular recognition between the azobenzene moiety on the surface of AuNPs and free α‐CD.

     

Synthesis of New Hydrogels by Copolymerization of Poly(2‐methyl‐2‐oxazoline) Bis(macromonomers) and N‐Vinylpyrrolidone

New non‐ionic hydrogels were synthesized by radical homopolymerization of vinyl end‐functionalized poly(2‐methyl‐2‐oxazoline) bis(macromonomers), or by radical copolymerization of these bis(macromonomers) with N‐vinyl‐2‐pyrrolidone (NVP). The poly(2‐methyl‐2‐oxazoline) bis(macromonomers) were synthesized through “living” cationic ring‐opening polymerization of 2‐methyl‐2‐oxazoline (MeOXA), using, simultaneously, the known “initiating” and “end‐capping” method for synthesis of macromonomers. Chloromethyl styrene was used as initiator and N‐(4‐vinylbenzyl)‐piperazine was used as the terminating agent. Well defined poly(2‐methyl‐2‐oxazoline) bis(macromonomers) were obtained with P_n = 4, 11, and 17. The hydrogel structures were characterized by high‐resolution magic angle spinning NMR technique and their solvent absorption capacity was tested by swelling experiments in different solvents. The bis(macromonomers) were characterized by NMR spectroscopy and gel permeation chromatography.

Schematic of polymerization     

A High‐Mobility Low‐Bandgap Copolymer for Efficient Solar Cells

A new high‐mobility low‐bandgap polymer, PBDT‐DODTBT, based on benzodithiophene and 5,6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)benzothiadiazole has been synthesized through a standard Stille coupling reaction. The polymer is soluble in common organic solvents, such as chloroform, tetrahydrofuran, and chlorobenzene and has excellent film forming properties. Preliminary studies of the copolymer showed the charge mobility as high as 7.15 × 10^?3 cm² · V^?1 · s^?1 from SCLC measurement. Initial photovoltaic cells based on the composite structure of ITO/PEDOT:PSS/PBDT‐DODTBT: ^α PC₇₁BM (1:2)/Ca/Al showed an open‐circuit voltage of 0.76 V, a power conversion efficiency of 4.02%, and a short‐circuit current of 8.96 mA · cm^?2.

     

Coassembly Modulated pH‐Responsive Hydrogel for Dye Absorption and Release

Hydrogel as a carrier for drug delivery system has been developed, but it is hard to change the load and release of drugs through a simple way. Herein, the authors report a novel pH‐sensitive supramolecular binary hydrogel based on Phe‐Gly derivative gelator (LPPG) and 4,4′‐dipyridine disulfide (DPDS). Fourier transform infrared spectroscopy, circular dichroism, and ¹H NMR confirm that the driving force for the coassembly process is intermolecular hydrogen bonds. The composite hydrogel can improve the dye adsorption capacity relative to LPPG hydrogel. Moreover, the controllable absorption of the dyes is studied by varying the pH and concentration of dye solutions. LPPG‐DPDS hydrogel can also release of entrapped dyes at physiological pH. The two‐component hydrogel should be a promising system for controllable drug delivery.

     

Tunable High‐Molecular‐Weight Anion‐Exchange Membranes for Alkaline Fuel Cells

Tunable alkaline anion‐exchange membranes based on QPMBV are synthesized using a bottom‐up approach, miniemulsion copolymerization, which can incorporate functional groups into the copolymers with designated composition and high molecular weight. The mechanical and electrochemical properties of the obtained QPMBV membranes are tuned by varying the composition. It is found that the ion exchange capacity of the copolymer, the hydrophilicity of the copolymer chains, the molecular weight, and the glass transition temperature of the copolymers are essential to balance the mechanical and OH^– transport properties of QPMBV membranes. QPMBV membrane fuel cells show the best power output and the long‐lasting fuel cell performance among the APE membranes in open literature.

     

Benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐terthiophene Copolymers Containing Styryl‐Triphenylamine Side Chains: Synthesis and Photovoltaic Performance Optimization with Fullerene Acceptors

A new two‐dimensional‐conjugated polymer (PBDTT3‐TPA) containing benzodithiophene (BDT) and a side chain isolation comonomer is designed and synthesized. Interestingly, PBDTT3‐TPA is compatible with higher lowest unoccupied molecular level (LUMO) acceptors of indene‐C₆₀ bisadduct (ICBA), and polymer solar cells based on PBDTT3‐TPA/ ICBA show an open‐circuit voltage (V_OC) of ca. 0.80 V and a power conversion efficiency of 2.48% under AM1.5G illumination of at 100 mW cm^?2. Furthermore, the energy loss in the corresponding fullerene acceptor devices is discussed, and the increase in the observed V_OC is explained quantitatively by the up‐shifted LUMO energy of ICBA (0.17 eV) and the reduced saturation current (J_SO) in the blends.