A Facile One‐Pot Synthesis to Dextran‐Based Nanoparticles with Carboxy Functional Groups

Summary: Stabilized nanoparticles functionalized with carboxy groups were synthesized directly from dextran and acrylic acid (AA), without using any organic solvent and surfactant. The composition and morphology of these dextran‐based nanoparticles, as well as the mechanism of this one‐pot synthesis, were also investigated in this paper. This approach is anticipated to be applicable to various water‐soluble polysaccharides to fabricate nanoparticles facilely.

Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA.     

Chain Growth Polycondensation as a Polymer Generating Reaction in the Synthesis of Oligo(p‐phenyleneethynylene)s with Low Polydispersity

Summary: The polycondensation of 1‐ethynyl‐2,5‐dihexyl‐4‐iodobenzene in the presence of 1‐ethynyl‐2,5‐dihexyl‐4‐(2‐phenylethynyl)benzene proceeds according to the mechanism of initiated chain growth polycondensation. It has allowed the synthesis of oligomers with a desired molecular weight and a narrow molecular weight distribution. The reasons for the side reaction leading to the formation of diyne compounds are revealed and the presumed mechanism is given. This opens prospects for the preparation of defectless poly(p‐phenyleneethynylene)s with required molecular weights and narrow molecular weight distributions.

     

Photodeformable Polymers: A New Kind of Promising Smart Material for Micro‐ and Nano‐Applications

Summary: Starting in the 1960s, several kinds of photodeformable polymers have been developed, such as monolayers, polymer gels, solid films and liquid‐crystalline elastomers with different photodeformation mechanisms. This field evolved slowly until recently when significant achievements have been made. Most recently, Lendlein and co‐workers have put forward another new concept – using photo‐crosslinking to prepare deformable polymers with various pre‐determined shapes (Nature 2005 , 434, 879). This highlight gives a general introduction into photodeformable polymers and brings forth future challenges.

A polymer film doped with SCAA molecules where (a) is the permanent shape, (b) is the temporary shape and (c) is the recovered shape.     

Thermosensitive Hollow Capsules Based on Thermoresponsive Polyelectrolytes

Thermosensitive hollow capsules were successfully fabricated by the layer‐by‐layer deposition onto colloid particles of oppositely charged diblock copolymers each containing a poly(N‐isoproprylacrylamide) (PNIPAM) block and by the subsequent decomposition of the core. The multilayer growth was characterized by electrophoresis and single particle light scattering. By combining confocal microscopy observation and FRAP measurements, we showed that the morphology and the permeability of the capsules change upon heating in aqueous solution. The decrease of size accompanied by a decrease of the permeability with increasing temperature was attributed to structural rearrangements in the shell. However, this process is only partially reversible upon cooling, limiting the thermoresponsive behavior of the capsules.

CLSM images of hollow capsules in presence of 6‐carboxyfluorescein (left) and fluorescein‐labeled dextran (right).     

Preparation and Properties of Cholesteric Network Polymers Based on Liquid Crystalline Epoxides

Summary: Polyether network polymers with cholesteric superstructure are formed by the photochemically induced cationic copolymerisation of a nematic diepoxide with chiral epoxides. If a cholesteric superstructure is formed or not, depends on the temperature at which the photopolymerisation is carried out. The storage modulus is higher above T_G in samples with cholesteric superstructure. Optical rotations and vibrational circular dichroism spectra (VCD) depend strongly on the surface state of the substrates. From the VCD spectra it is concluded that the copolymerisation leads to different superstructures depending on the rub directions of the substrates.

IR absorption spectrum and VCD spectrum of the cholesterol derivative 4 .     

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.     

Cover Picture: Macromol. Chem. Phys. 21/2005

Summary: In this paper, we describe the multiple morphogenesis of poly(ethyleneimine) (PEI)‐directed silicas through the facile tuning of the media in which the PEIs pre‐organize. The silica shapes and structures ranged from nanofiber‐based asters, fans, particles, plates, and/or curved films to large aggregates composed of unit nanoribbon structures and networks that contained nanospheres or particles, depending on the media compositions or media modulations coupled with the polymer concentrations and chain architectures. We found that the media modulations not only controlled the formation of the silica unit structures but also manipulated the hierarchical structures based on the unit silicas. Furthermore, methanol modulation successfully allows us to elucidate the dependence of silica deposition ability on the polymer chain architectures that cause subtle differences in their aggregates. The approach of methanol modulation to obtain shaped silicas, which involves both PEI aggregation and silica deposition at room temperature, is of particular interest to applications for the immobilization of bioactive components.

     

Large Area Monodomain Order in Colloidal Crystals

Summary: In previous papers, a novel melt process was reported for the preparation of colloidal crystals exhibiting the crystalline structure of opals. Latex spheres with a hard, crosslinked core and a grafted‐on elastomeric shell flow at elevated temperatures under uniaxial compression much like other polymer melts. However, the spheres start crystallizing at the plates of the press, whereupon the crystalline order grows, layer by layer, into the flowing melt. In this report, the domain order of opal disks thus obtained is discussed, together with the phenomena of light reflection. The pattern of light reflected from the (220) plane of the fcc lattice reveals that, during compression, this lattice is oriented macroscopically by the radial melt flow so that each radial sector of the opal disk forms a crystalline monodomain.

Film of latex spheres with colloidal crystalline order prepared by melt compression of PS/PMMAcsPEA core‐shell latex spheres.     

Modification of Polyethylene by VUV Irradiation in the Presence of Trimethylsilane and Oxygen

The photoassisted modification of LDPE by VUV irradiation in a reactive trimethylsilane/oxygen atmosphere was investigated. The modified LDPE surface was investigated by FT‐IR, XPS, contact‐angle measurements and electron microscopy. Attachment of alkylsilyl and Si–O units to LDPE was observed. Best results were obtained using an equimolar trimethylsilane/oxygen mixture. Low‐energy surfaces were obtained after a few minutes of irradiation at an intensity of 1.7 mW · cm^?2. After prolonged irradiation, the thickness of the modified polyethylene layer is approximately 700 nm. Surface modifications of this type may be of interest to obtain protective and barrier layers on polyolefins.

     

Synthesis and Characterization of Hyperbranched Polyethylenes Made with Nickel‐α‐Diimine Catalysts

The polymerization of ethylene in the presence of 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediiminenickel(II) dichloride ( 1 ) and methylaluminoxane (MAO) gives hyperbranched polyethylene (HBPE) in appropriate reaction conditions. The system 1 /MAO is active in solvents like toluene or hexane at temperatures as high as 80 °C and ethylene pressures ranging from 1 to 15 atm. The polyethylenes obtained show high molecular weights (up to 467 kg · mol^?1) and more than 218 branches per 1 000 backbone carbon atoms, qualifying these materials as hyperbranched. Dynamic‐mechanical thermal analysis (DMTA) of these materials shows high β‐transitions, directly related to the branch content of these polyethylenes.

DMTA analysis of polyethylenes obtained with 1 /MAO at 0, 30, and 50 °C (corresponding to entries 1, 2 and 3).     

Polyrotaxanes of Pyrene–Triazole Conjugated Azomethine and α‐Cyclodextrin with High Fluorescence Properties

The paper reports on the preparation of a new 2‐rotaxane monomer through an acid coupling reaction between 1‐pyrenecarboxaldehyde and α‐CD/3,5‐diamino‐1,2,4‐triazole inclusion complex. Pyrenyl groups are large enough to provide a blocking effect toward cyclodextrin de‐threading. The oxidative C? C coupling of 2‐rotaxane in the presence of RuCl₃ catalyst afforded conjugated azomethine polyrotaxanes. The expected modifications of the solubility, morphology, film forming ability for rotaxane polymer were proved. As shown by fluorescence and UV‐vis spectroscopy, a material with optical properties appropriate for use in photonics was obtained.

     

Chemical Binding of Unsaturated Fluorenes to Poly(2‐chloroxylylene) Thin Films

A series of substituted fluorenes with vinyl groups as reactive sites were synthesized and characterized. Fluorene‐based polymers with vinyl groups as end chains and side chains functionalities were also prepared. In both cases, successful preparation of functionalized Parylene C films (modylayers) was achieved. The set of spectral methods used has allowed us to conclude that such functionalization is based on the chemical reaction of double bonds with xylylene radicals during deposition process. Parylene C films chemically modified with specially synthesized polyfluorenes showed PL quantum efficiency comparable with neat polyfluorenes.

     

Synthesis of Polyphenylene Ether Derivatives: Estimation of Their Dielectric Constants

A series of poly(2‐alkyl‐6‐phenylphenylene ether)s were prepared by the oxidative polymerization of 2‐alkyl‐6‐phenylphenols. Their dielectric constants were approximately 2.5, whereas it was found that the phenyl group at the 6‐position clearly increased the Q factor of the polymer compared with poly(2,6‐dimethylphenylene ether), PPE. These values were qualitatively predicted from the polarizability and the molar volume calculated by the theoretical analysis of the unit structure at the HF/6‐31G* level.

     

Macromol. Chem. Phys. 13/2011

Reactive blending of functionalized polyethylenes (PE) and polyamides (PA) is performed by carefully choosing extrusion conditions and polymeric materials in order to obtain two types of stable morphologies. The first blend type yields a co‐continuous morphology and the second type a dispersion of sub‐micron droplets of the PA phase in a PE matrix. The crystallization kinetics of the PA change from a sigmoidal classical type (for the co‐continuous blend) to first‐order kinetics in the case of the sub‐micron PA droplets. The results demonstrate an intimate relationship between blend morphology and nucleation and crystallization kinetics of the blend components.

     

Nanoscale Blends between Immiscible Polymers via Simultaneous Non‐Interfering Polymerisation

Summary: An important topic in polymer science seeks to improve the performances of polymer blends using nanoscale phase segregation. Here, blends between polystyrene and polycaprolactone are realised by a chemical route. The non‐interfering character of the radical polymerisation of styrene and the lanthanide halide initiated ring‐opening polymerisation of caprolactone is assessed. The molecular weights range from 2 000 to 3 500 for polycaprolactone and up to 140 000 for polystyrene, with reasonable polydispersity indexes. From calorimetry measurements, it is shown that polystyrene and low molecular weight polycaprolactone are immiscible. The morphology of the blends between the two immiscible polymers studied by atomic force microscopy is consistent with nanometer‐scale phase segregation.

AFM surface image of a nanoscale blend.     

Versatile Synthesis of Soluble Multifunctional Thiophene Copolymers with NLO Activity

Functionalized second‐order nonlinear optical (NLO) thiophene copolymers were synthesized. Two elegant syntheses based on the post‐functionalization of polymeric precursors obtained by oxidative polymerization were developed, leading to copolymers that proved to be fully soluble in common organic solvents. The new materials were characterized by NMR, FT‐IR, and UV‐vis spectroscopies, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Moreover, the NLO activity of the new materials, as determined by corona poling alignment and second harmonic generation (SHG) measurements, showed a good agreement between the second‐order NLO coefficient and the chromophore concentration.

Three‐dimensional optimization of the chromophore thiophene‐functionalized comonomer.     

Syndiotactic Polystyrene Films: Orientation and Structural Changes Upon Biaxial Drawing

The orientation developed in biaxially stretched sPS (BoSPS) films before and after crystallization is studied using XRD and FT‐IR. On BoSPS films, thermal treatment induces crystallization into the trans‐planar α‐crystalline phase and a “planar” crystalline phase orientation is observed. In contrast, solvent treatments on BoSPS films induce crystallization into the helical δ‐crystalline phase, representing the first example of a polymeric framework that is able to absorb low‐molecular‐mass guest molecules from water and air at low activities and that is promising for applications in chemical separation or water purification applications; in this case a high degree of a_//c_// “uniplanar” crystalline phase orientation is observed.

     

New Second‐Order Nonlinear Optical Polymers Derived from AB2 and AB Monomers via Sonogashira Coupling Reaction

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.

     

New Materials for Rapid Prototyping Applications

Summary: Rapid prototyping (RP) is a widely used manufacturing tool in the product development cycle. This Highlight article gives a brief overview of the currently available RP techniques with special emphasis on three‐dimensional (3D) printing. The advantages and drawbacks of various RP processes regarding material quality, feature resolution, and surface quality are pointed out. New developments in the field of material development allow the use of polymer ionomers for 3D printing. Using polymer ionomers some of the drawbacks of 3D printing can be eliminated. In particular, the mechanical strength can be increased compared to traditional powder systems used for 3D printing. This article describes the chemical background of polymer ionomers and the relevance of these materials for future developments in RP.

Cellular structures made of photopolymerizable polymers.     

Synthesis of Ethylene/Acrylonitrile Composite Elastomers with Nanosized Polyacrylonitrile Domains Using α‐Dimine‐[N,N] Nickel Dichloride/EASC

A series of ethylene and acrylonitrile composite elastomers were prepared using (1,4‐bis(2,6diisopropylphenyl)‐acenaphtenediimine‐nickel(II))‐dichloride/ethylaluminum sesquichloride (EASC). The xylene‐soluble polymer fraction showed nitrile bands in infrared spectroscopy at 2 245 and 2 214 cm^?1 and polyacrylonitrile‐enriched structures were detected in the xylene‐insoluble fraction by¹H and ¹³C NMR. In addition, TEM detected nanosized polyacrylonitrile domains dispersed in the polyethylene matrix. Differential scanning calorimetry scans conducted from ?70 to 350 °C measured exothermic bands corresponding to the cyclization and aromatization of the nitrile groups dispersed in the polyethylene matrix.