Fluorene-Based Copolymers Containing Dinaphtho-s-indacene as New Building Blocks for High-Efficiency and Color-Stable Blue LEDs

By incorporating a new building block, 7,7,15,15-tetraoctyldinaphtho-s-indacene (NSI), into the backbone of poly(9,9-dioctylfluorene) (PFO), a novel series of blue light-emitting copolymers (PFO-NSI) have been developed. The insertion of the NSI unit into the PFO backbone leads to the increase of local effective conjugation length, to form low-energy fluorene-NSI-fluorene (FNF) segments that serve as exciton trapping sites, to which the energy transfers from the high-energy PFO segments. This causes these copolymers to show red-shifted emissions compared with PFO, with a high efficiency and good color stability and purity. The best device performance with a luminance efficiency of 3.43 cd . A(-1), a maximum brightness of 6 539 cd . m(-2) and CIE coordinates of (0.152, 0.164) was achieved.

Core Crosslinking of Biodegradable Block Copolymer Micelles Based on Poly(ester carbonate)

A biodegradable amphiphilic block copolymer, PEG-b-P(LA-co-MAC), was used to prepare spherical micelles consisting of a hydrophobic P(LA-co-MAC) core and a hydrophilic PEG shell. To improve their stability, the micelles were crosslinked by radical polymerization of the double bonds in the hydrophobic blocks. The crosslinked micelles had similar sizes and a narrow size distribution compared to their uncrosslinked precursor. The improved stability of the crosslinked micelles was confirmed by measurements of the CMC and a thermodynamic investigation. These micelles can internalize into Hela cells in vitro as demonstrated by inverted fluorescence microscopy and CLSM. These stabilized nanoscale micelles have potential use in biomedical applications such as drug delivery and disease diagnosis.

Oxygen Carrier Based on Hemoglobin/Poly(L-lysine)-block-poly(L-phenylalanine) Vesicles

An oxygen carrier was prepared by encapsulating carbonylated hemoglobin (CO-Hb) molecules into polypeptide vesicles made from poly(L-lysine)-block-poly(L-phenylalanine) (PLL-b-PPA) diblock copolymers in aqueous medium at pH 5.8. The encapsulation was confirmed by confocal laser scanning microscopy (CLSM). The morphology and size of the Vesicles were studied by field-emission scanning electron microscopy (ESEM). They had a spherical shape with it mean diameter of about 4 to 5 mu m. The encapsulation efficiency of hemoglobin was 40 wt %, and the hemoglobin content in the vesicles was 32 wt %. The CO-Hb encapsulated in the PLL-b-PPA vesicles was more stable than free CO-Hb under ambient conditions, In the presence of a O-2 atmosphere, the CO-Hb in the vesicle could be converted into oxygen-binding hemoglobin (O-2-Hb) under irradiation of visible light for 2 h. Therefore, the CO-Hb/PLL-b-PPA vesicles are expected to be used its red blood cell substitutes.

Synthesis, self-assembly in water, and cytotoxicity of MPEG-block-PLLA/DX conjugates

Docetaxel (DX) is one of the most effective antineoplastic drugs. Its current clinical administration is limited because of its hydrophobicity and Serious side effects. A polymer/DX conjugate is designed and successfully prepared to solve these problems. It is monomethoxy-poly(ethylene glycol)-block-poly(L-lactide)/DX (MPEG-PLLA/DX) It was synthesized by reacting DX with carboxyl-terminated copolymer MPEG-PLLA, which was prepared by reacting succinic anhydride with hydroxyl-terminated copolymer monomethoxy-poly(ethylene glycol)-block-poly (L-lactide) (MPEG-PLLA). Its structure and molecular weight was confirmed by H-1 NMR and GPC. The MPEG-PLLA/DX micelles in aqueous solution were prepared Using a SO]vent displacement method and characterized by dynamic light scattering for size and size distribution, and by transmission electron microscopy for surface morphology. Its antitumor activity against HeLa cancer cells evaluated by MTT assay showed that it had a similar antitumor activity to Pure D at the same drug content.

Multi-armed poly(L-glutamic acid)-graft-oligoethylenimine copolymers as efficient nonviral gene delivery vectors

Background The application of polyethylenimine (PEI) in gene delivery has been severely limited by significant cytotoxicity that results from a nondegradable methylene backbone and high cationic charge density. It is therefore necessary to develop novel biodegradable PEI derivates for low-toxic, highly efficient gene delivery.Methods A series of novel cationic copolymers with various charge density were designed and synthesized by grafting different kinds of oligoethylenimine (OEI) onto a determinate multi-armed poly(L-glutamic acid) backbone. The molecular structures of multi-armed poly(L-glutamic acid)-graft-OEI (MP-g-OEI) copolymers were characterized using nuclear magnetic resonance, viscosimetry and gel permeation chromatography. Moreover, the MP-g-OEI/DNA complexes were measured by a gel retardation assay, dynamic light scattering and atomic force microscopy to determine DNA binding ability, particle size, zeta potential, complex formation and shape, respectively. MP-g-OEI copolymers were also evaluated in Chinese hamster ovary and human embryonic kidney-293 cells for their cytotoxicity and transfection efficiency.

Synthesis of symmetric H-shaped block copolymer by the combination of ATRP and living anionic polymerization

A novel fluorescent dye labeled H-shaped block copolymer, (PMMA-Fluor-PS)(2)-PEO-(PS-Fluor-PMMA)(2), is synthesized by the combination of atom transfer radical polymerization (ATRP) and anionic polymerization (AP). To obtain the designated structure of the copolymer, a macroinitiator, 2,2-dichloro acetyl-PEO-2,2-dichloro acetyl (DCA-PEO-DCA), was prepared from DCAC and poly(ethylene oxide). The copolymer was characterized by H-1 NMR, GPC and fluorescence spectroscopy.

Synthesis of a (sic)-shaped amphiphilic block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

The functionalization of monomer units in the form of macroinitiators in an orthogonal fashion yields more predictable macromolecular architectures and complex polymers. Therefore, a new there exists E-shaped amphiphilic block copolymer, (PMMA)(2)-PEO-(PS)(2)-PEO-(PMMA)(2) [where PMMA is poly(methyl methacrylate), PEO is poly (ethylene oxide), and PS is polystyrene], has been designed and successfully synthesized by the combination of atom transfer radical polymerization (ATRP) and living anionic polymerization. The synthesis of meso-2,3-dibromosuccinic acid acetate/diethylene glycol was used to initiate the polymerization of styrene via ATRP to yield linear (HO)(2)-PS2 with two active hydroxyl groups by living anionic polymerization via diphenylmethylpotassium to initiate the polymerization of ethylene oxide. Afterwards, the synthesized miktoarm-4 amphiphilic block copolymer, (HO-PEO)(2)-PS2, was esterified with 2,2-dichloroacetyl chloride to form a macroinitiator that initiated the polymerization of methyl methacrylate via ATRP to prepare the there exists E-shaped amphiphilic block copolymer.

Tethered diblock copolymer chains on platelets prepared by semicrystalline ABC triblock copolymers in toluene with trace amounts of water

Lamellar platelets of triblock copolymers grown in dilute toluene solution with trace amounts of water can be used as templates for tethered diblock copolymer chain preparation and analysis. Polystyrene-bpoly(2-vinylpyridine)-b-poly(ethylene oxide) (PS-b-P2VP-b-PEO) with two different block fractions were used as model templates to generate tethered P2VP-b-PS chains on the platelet basal surfaces. In toluene solution the aggregation states of PS-b-P2VP-b-PEO were sensitive to the water content in the solution. For toluene with trace amount of water, spherical micelles were formed in the early stage and large square platelets would gradually grow from these spherical micelles. The hydrogen bonding between water and EO units was responsible for the formation of micelles and subsequent square platelets in the solution. Tethered P2VP-b-PS chains on basal surface of PEO platelets could be regarded as diblock copolymer brushes and the density (or: 0.086-0.36) and height (d: 3.5-14.3 nm) of these tethered chains could be easily modulated by changing the crystallization condition and/ or the molecular weight of each block. The tethered P2VP-b-PS chains were responsive to different solvent vapor.

Development of nanodomain and fractal morphologies in solvent annealed block copolymer thin films

We have systematically studied the thin film morphologies of asymmetric polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer subjected to solvent vapors of varying selectivity for the constituent blocks. Upon a short treatment in neutral or PS-selective vapor, the film exhibited a highly ordered array of hexagonally packed, cylindrical microdomains. In the case of PEO selective vapor annealing, such ordered cylindrical microdomains were not obtained. instead, fractal patterns on the microscale were observed and their growth processes investigated. Furthermore, hierarchical structures could be obtained if the fractal pattern was exposed to neutral or PS selective vapor.

Synthesis and crystallization behaviors of poly(styrene-b-isoprene-b-epsilon-caprolactone) triblock copolymers

The triblock copolymers, poly(styrene-b-isoprene-b-epsilon-caprolactone)s (PS-b-PI-b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS-b-PI-OH was synthesized by sequential- anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS-b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS-b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL27, PCL328 and PS-b-PI-b-PCL344 are 0.71, 0.46 and 0.07 mu m s(-1), respectively. The atomic force microscopy (AFM) images of the PS90-b-PI66-b-PCL-(28) show the columns morphology formed by it's self-assembling.

Synthesis and characterization of electroactive and biodegradable ABA block copolymer of polylactide and aniline pentamer

A triblock copolymer PLA-b-AP-b-PLA (PAP) of polylactide (PLA) and aniline pentamer (AP) with the unique properties of being both electroactive and biodegradable is synthesized by coupling an electroactive carboxyl-capped AP with two biodegradable bihydroxyl-capped PLAs via a condensation reaction. Three different molecule weight PAP copolymers are prepared. The PAP copolymers exhibit excellent electroactivity similar to the AP and polyaniline, which may stimulate cell proliferation and differentiation. The electrical conductivity of the PAP2 copolymer film (similar to 5 x 10(-6) S/cm) is in the semiconducting region. Transmission electron microscopic results suggest that there is microphase separation of the two block segments in the copolymer, which might contribute to the observed conductivity. The biodegradation and biocompatibility experiments in vitro prove the copolymer is biodegradable and biocompatible. Moreover, these new block copolymer shows good solubility in common organic solvents, leading to the system with excellent processibility. These biodegradable PAP copolymers with electroactive function thus possess the properties that would be potentially used as scaffold materials for neuronal or cardiovascular tissue engineering.

Morphology, tensile strength and thermal behavior of isotactic polypropylene/syndiotactic polystyrene blends compatibilized by SEBS copolymers

The effects of three triblock copolymers of poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) of different molecular weight (MW) on the morphology, tensile strength and thermal behavior of isotactic polypropylene/syndiotactic polystyrene (iPP/sPS, 80/20) blend are investigated. Morphology observation shows that both the medium MW and the lower MW SEBS are more effective than the higher MW SEBS in compatibilizing the blends. Tensile tests revels both the medium and low MW compatibilizer lead to a significant improvement in tensile strength, while the higher MW compatibilizer is efficient in increasing the elongation at break of the blends. The localization of compatibilizers in the blends is observed by mean of SEM and the correlation between the distribution of the compatibilizers and mechanical properties of the blends is evaluated. The mechanical properties of the iPP/sPS blends depend on not only the interfacial activity of the compatibilizers but also the distribution of the compatibilizer in the blend. Addition of the compatibilizers to the blend causes a remarkable decrease in the magnitude of the crystallization peak of sPS at its usual T-c. Vicat softening points demonstrate that the heat resistance of iPP/sPS blend is much higher than that of the pure iPP.

Multiple morphologies and their transformation of a polystyrene-block-poly(4-vinylpyridine) block copolymer

We report the multiple morphologies and their transformation of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) in low-alkanol solvents. In order to improve the solubility of polystyrene block in alcohol solvents, the solution of block copolymer sample was treated at a higher temperature, and then the influence of rate of decreasing temperature on multiple morphologies (including spheres, rods, vesicles, porous vesicles, large compound vesicles, and large compound micelles) was observed. The transformation of spheres to rods, to tyre-shaped large compound micelles, and to sphere-shaped large compound micelles was also realized. The formation mechanisms of the multiple morphologies and their transformation are discussed briefly.

Synthesis and characterization of poly(epsilon-caprolactone)-poly(L-lactide) diblock copolymers with an organic amino calcium catalyst

The quasiliving characteristics of the ringopening polymerization of epsilon-caprolactone (CL) catalyzed by an organic amino calcium were demonstrated. Taking advantage of this feature, we synthesized a series of poly (F-caprolactone) (PCL)-poly(L-lactide) (PLA) cliblock copolymers with the sequential addition of the monomers CL and L-lactide. The block structure was confirmed by H-1-NMR, C-13-NMR, and gel permeation chromatography analysis. The crystalline structure of the copolymers was investigated by differential scanning calorimetry and wide-angle X-ray diffraction analysis. When the molecular weight of the PLA block was high enough, phase separation took place in the block copolymer to form PCL and PLA domains, respectively.

Study on the origin of inverted phase in drying solution-cast block copolymer films

In a previous study, we reported observation of the novel inverted phase (the minority blocks comprising the continuum phase) in kinetically controlled phase separating solution-cast poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer films [Zhang et al. Macromolecules 2000, 33, 9561-7]. In this study, we adopt the same approach to investigate the formation of inverted phase in a series of solution-cast poly(styrene-b-butadiene) (SB) asymmetric diblock copolymers having nearly equal polystyrene (PS) weight fraction (about 30 wt %) but different molecular weights. The microstructure of the solution-cast block copolymer films resulting from different solvent evaporation rates, R, was inspected, from which the kinetically frozen-in phase structures at qualitatively different block copolymer concentrations and correspondingly different effective interaction parameter, chieff, can be deduced. Our result shows that there is a threshold molecular weight or range of molecular weight below which the unusual inverted phase is accessible by controlling the solvent evaporation rate. In comparing the present result with that of our previous study on the SBS triblock copolymer, we find that the formation of the inverted phase has little bearing on the chain architecture. We performed numerical calculations for the free energy of block copolymer cylinders and found that the normal phase is always preferred irrespective of the interaction parameter and molecular weight, which suggests the formation of the inverted phase to have a kinetic origin.