Synthesis of a novel structural triblock copolymer of poly(gamma-benzyl-L-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone)

A novel structural triblock copolymer of poly(gamma-benzyl-L-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PBLG-PEO-PCL) was synthesized by a new approach in the following three steps: (1) sequential anionic ring opening polymerization (ROP) of ethylene oxide and epsilon-caprolactone with an acetonitrile/potassium naphthalene initiator system to obtain a diblock copolymer CN-PEO-PCL with a cyano end-group; (2) conversion of the CN end-group into NH2 end-group by hydrogenation to obtain NH2-PEO-PCL; (3) ROP of gamma-benzyl-L-glutamate-N-carboxyanhydrides (Bz-L-GluNCA) with NH2-PEO-PCL as macroinitiator to obtain the target triblock copolymer. The structures from CN-PEO precursor to the triblock copolymers were confirmed by FT-IR and H-1 NMR spectroscopy, and their molecular weights were measured by gel permeation chromatography. The monomer of Bz-L-GluNCA can react almost quantitatively with the amino end-groups of NH2-PEO-PCL macroinitiator by ROP.

Study on crystalline morphology of poly(L-lactide)-poly(ethylene glycol) diblock copolymer

Crystallization behavior, structural development and morphology evolution in a series of diblock copolymers Of poly(L-lactide)-blockpoly(ethylene glycol) (PLLA-b-PEG) were investigated via differential scanning calorimetry, wide-angle X-ray diffraction, polarized optical microscopy and atomic force microscopy. In these copolymers, both blocks are crystallizable and biocompatible. It was interesting that these PLLA-b-PEG diblock copolymers could form spherulites with banded textures, which was undercooling dependent. Single crystals with an abundance of screw dislocations were also observed via AFM. Such results indicated that these ringed spherulites and single crystals were formed during the crystallization of the PLLA blocks.

Thermal and crystalline properties of random copolymer of CL and DTC prepared by La(OAr)(3)

Thermal and crystalline properties of random copolymer of epsilon-caprolactone (CL) and 2,2-dimethyl trimethylene carbonate (DTC) prepared by lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) (La(OAr)(3)) have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and wide-angle X-ray diffraction (WAXD). Fox equation interprets the relationship between glass transition temperature (T-g) and copolymer compositions. T-g decreases from PDTC (16.7degreesC) to PCL (-65.1degreesC), reflecting the internal plasticizing effect of CL units on DTC units in the copolymers. The introduction of CL units to PDTC can effectively improve its heat resistance. Small amount of DTC (5% molar) in PCL chain improves the mechanical properties of the polymer, which had elongation of 1000, much higher than that of PCL (8.8).

Synthesis and characterization of the paclitaxel/MPEG-PLA block copolymer conjugate

A paclitaxel/MPEG-PLA block copolymer conjugate was prepared in three steps: (1) hydroxyl-terminated diblock copolymer of monomethoxy-poly(ethylene glycol)-b-poly(lactide) (MPEG-PLA) was synthesized by ring-opening polymerization of L-lactide using MPEG as a maroinitiator, (2) it was converted to carboxyl-terminated MPEG-PLA by reacting with mono-i-butyl ester of diglycolic acid and subsequent deprotecting the t-butyl group with TFA; (3) the latter was reacted with paclitaxel in the presence of dicyclohexylcarbodiimide and dimethylaminopyridine. Structures of the polymers synthesized were confirmed by H-1 NMR, and their molecular weights were determined by gel permeation chromatography. The antitumor activity of the conjugate against human liver cancer H7402 cells was evaluated by MTT method. The results showed that paclitaxel can be released from the conjugate without losing cytotoxicity.

Micellization and reversible pH-sensitive phase transfer of the hyperbranched multiarm PEI-PBLG copolymer

A novel, hyperbranched, amphiphilic multiarm biodegradable polyethylenimine-poly(gamma-benZyl-L-gluta- mate) (PEI-PBLG) copolymer was prepared by the ring-opening polymerization of gamma-benzyl-L-glutamate-N-car-boxyanhydride (BLG-NCA) with hyperbranched PEI as a macroinitiator. The copolymer could self-assemble into core-shell micelles in aqueous solution with highly hydrophobic micelle cores. As the PBLG content was increased, the size of the micelles increased and the critical micelle concentration (CMC) decreased. The surface of the micelles had a positive potential. The cationic micelles were capable of complexing with plasmid DNA (pDNA), which could be released subsequently by treatment with polyanions. The PEI-PBLG copolymer formed unimolecular micelles in chloroform solution. ne pH-sensitive phase-transfer behavior exhibited two critical pH points for triggering the encapsulation and release of guest molecules. Both the encapsulation and release processes were rapid and reversible. Under strong acidic or alkaline conditions, the release process became partially or completely irreversible.

Interfacial electronic structure of copper phthalocyanine and copper hexadecafluorophthalocyanine studied by photoemission

Electronic structures of the heterojunction between copper phthalocyanine (CuPc) and copper hexadecafluorophthalocyanine (F16CuPc) were studied with ultraviolet photoemission spectroscopy. Band bending and an interface dipole were observed at the interface due to the formation of an electron accumulation layer and a depletion layer in F16CuPc and CuPc, respectively. Such an energy level alignment leads to interesting ambipolar characteristics for application of the CuPc/F16CuPc junction in organic field-effect transistors.

Solvent-induced novel morphologies in diblock copolymer blend thin films

We report the morphology and phase behaviors of blend thin films containing two poly styrene-b-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymers with different blending compositions induced by a selective solvent for the PMMA block, which were studied by transmission electron microscopy (TEM). The neat asymmetric PS-b-PMMA diblock copolymers employed in this study, respectively coded as a(1) and a(2), have similar molecular weights but different volume fractions of PS block (f(PS) = 0.273 and 0.722). Another symmetric PS-b-PMMA diblock copolymer, coded as s, which has a PS block length similar to that of a(1), was also used. For the asymmetric a(1)/a(2) blend thin films, circular multilayered structures were formed. For the asymmetric a(1)/symmetric s blend thin films, inverted phases with PMMA as the dispersed domains were observed, when the weight fraction of s was less than 50%. The origins of the morphology formation in the blend thin films via solvent treatment are discussed. Combined with the theoretical prediction by Birshtein et al. (Polymer 1992, 33, 2750), we interpret the formation of these special microstructures as due to the packing frustration induced by the difference in block lengths and the preferential interactions between the solvent and PMMA block.

Influence of Mn-O-Mn bond angle on the magnetic and electronic properties in YBaMn2O5

The influence of the Mn-O-Mn bond angle on the magnetic and electronic properties of YBaMn2O5 was studied by density functional theory, which was implemented in the CASTEP code. In practical calculation, both G- and A-type antiferromagnetic (AFM) orderings were considered. The calculated results indicated that G-type is more stable than A-type, in agreement with both experiment and previous theoretical study. It is also interesting to note that a transition from G-type to A-type at an Mn-O-Mn angle of ca. 170 degrees was found upon increasing Mn-O-Mn angle. Therefore, the calculation suggested that what is essential to stabilize the G-type AFM state is the reduction of the Mn-O-Mn bond angle. For both magnetic orderings, the compound changes from semiconductor to metal with the increase of Mn-O-Mn angle.

Solvent-induced crystallization of spherical micelles formed by copolymer blends

We have followed the morphological evolution and crystallization process of spherical micelles formed by the mixture of polystyrene-b-poly(acrylic acid) (PS-b-PAA) and polystyrene-b-poly(2-vinylpyridine)b-poly(ethylene oxide) (PS-b-P2VP-b-PEO) (the core of the spherical micelles was made of P2VP and PAA blocks through hydrogen bonding in neutral solvent N,N-dimethylformamide, DMF) via DMF vapor treatment. Different phenomena, such as rupture of the film, formation of cylinder aggregates and regular square lamellae, were observed when the micelle film was treated in DMF for different times. At the early stage of annealing in DMF vapor, the micelle film became unstable and ruptured. Cylinder aggregates, within which the PEO blocks achieved the association and primary chain folding, formed as the mesophases before the nucleation of the PEO single crystals at this stage. Further treatment in DMF vapor resulted in the nucleation of the PEO blocks at the corners of quasi-square lamellae. Then a quite regular "sandwich" lamellar structure, constructed by a PEO single-crystal layer covered by two tethered layers of other amorphous blocks on the top and bottom crystal basal surfaces, formed when the film of micelles was annealed in DMF vapor for sufficient times.

Inverted to normal phase transition in solution-cast polystyrene-poly(methyl methacrylate) block copolymer thin films

We have investigated the inverted phase formation and the transition from inverted to normal phase for a cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer in solution-cast films with thickness about 300 nm during the process of the solution concentrating by slow solvent evaporation. The cast solvent is 1, 1,2,2-tetrachloroethane (Tetra-CE), a good solvent for both blocks but having preferential affinity for the minority PMMA block. During such solution concentrating process, the phase behavior was examined by freeze-drying the samples at different evaporation time, corresponding to at different block copolymer concentrations, phi. As phi increases from similar to 0.1 % (nu/nu), the phase structure evolved from the disordered sphere phase (DS), consisting of random arranged spheres with the majority PS block as I core and the minority PMMA block as a corona, to ordered inverted phases including inverted spheres (IS), inverted cylinders (IC), and inverted hexagonally perforated lamellae (IHPL) with the minority PMMA block comprising the continuum phase, and then to the lamellar (LAM) phase with alternate layers of the two blocks, and finally to the normal cylinder (NC) phase with the majority PS block comprising the continuum phase. The solvent nature and the copolymer solution concentration are shown to be mainly responsible for the inverted phase formation and the phase transition process.

Electronic structures of 3d-metal mononitrides

Bond distances, vibrational frequencies, electron affinities, ionization potentials, and dissociation energies of the title molecules in neutral, positively, and negatively charged ions were studied by use of density functional methods B3LYP, BLYP, BHLYP, BPW91, and B3PW91. The calculated results are compared with experiments and previous theoretical studies. It was found that the calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy and vibrational frequency. For neutral species, pure density functional methods BLYP and BPW91 have relatively good performance in reproducing the experimental bond distance and vibrational frequency. For cations, hybrid exchange functional methods B3LYP and B3PW91 are good in predicting the dissociation energy. For both neutral and charged species, BHLYP tends to give smaller dissociation energy.

Biodegradable amphiphilic triblock copolymer bearing pendant glucose residues: Preparation and specific interaction with Concanavalin A molecules

A novel biodegradable amphiphilic block copolymer PLGG-PEG-PLGG bearing pendant glucose residues is successfully prepared by the coupling reaction of 3-(2-aminoethylthio) propyl-R-D-glucopyranoside with the pendant carboxyl groups of PLGG-PEG-PLGG in the presence of N,N'-carbonyldiimidazole. The polymer PLGG-PEG-PLGG, i.e., poly {(lactic acid)-co-[(glycolic acid)-alt-(L-glutamic acid)]}-block-poly(ethylene glycol)-block-poly{( lactic acid)-co-[( glycolic acid)-alt-(L-glutamic acid)]}, is prepared by ring-opening copolymerization of L-lactide (LLA) with (3s)-benzoxylcarbonylethylmorpholine-2,5-dione (BEMD) in the presence of dihydroxyl PEG with molecular weight of 2000 as macroinitiator and Sn(Oct)(2) as catalyst, and then by catalytic hydrogenation. The glucose-grafted copolymer shows a lower degree of cytotoxicity to ECV-304 cells and improved specific recognition and binding with Concanavalin A (Con A). Therefore, this kind of glucose-grafted copolymer may find biomedical applications.

Synthesis and characterization of RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) triblock copolymer

Advances in tissue engineering require biofunctional scaffolds that can provide not only physical support for cells but also chemical and biological cues needed in forming functional tissues. To achieve this goal, a novel RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) (PEG-PLA-PGL/RGD) was synthesized in four steps (1) to prepare diblock copolymer PEG-PLA-OH and to convert its -OH end group into -NH2 (to obtain PEG-PLA-NH2), (2) to prepare triblock copolymer PEG-PLA-PBGL by ring-opening polymerization of NCA (N-carboxyanhydride) derived from benzyl glutamate with diblock copolymer PEG-PLA-NH2 as macroinitiator, (3) to remove the protective benzyl groups by catalytic hydrogenation of PEGPLA-PBGL to obtain PEG-PLA-PGL, and (4) to react RGD (arginine-glycine-(aspartic amide)) with the carboxyl groups of the PEG-PLA-PGL. The structures of PEG-PLA-PGL/RGD and its precursors were confirmed by H-1 NMR, FT-IR, amino acid analysis, and XPS analysis. Addition of 5 wt % PEG-PLA-PGL/RGD into a PLGA matrix significantly improved the surface wettability of the blend films and the adhesion and proliferation behavior of human chondrocytes and 3T3 cells on the blend films. Therefore, the novel RGD-grafted triblock copolymer is expected to find application in cell or tissue engineering.