Effect of hydrophobicity of monomers on the structures and properties of 1,3:2,4-dibenzylidene-D-sorbitol organogels and polymers prepared by templating the gels

The effects of hydrophobicity of monomers on the structures and properties of 1,3:2,4-dibenzylidene-D-sorbitol (DBS) organogels and nanostructured polymers prepared by templating the self-assembled organogels were investigated in this study. Hydrophobic styrene (St), hydrophilic methyl (methacrylate) (MMA), and their mixtures were chosen as the monomers. Though the gelation time varied, the average diameters (around 10 nm) of DBS nanofibrils found in the resulting organogels did not change significantly, for monomers of different hydrophobicity, as observed by transmission electron microscopy (TEM). Nonetheless, new structures, DBS microaggregates, appeared when the MMA content in the monomers was high enough. These irregular, micrometer-sized DBS structures (microaggregates) may have formed because the aggregated DBS molecules were influenced by the MMA monomers, due to the hydrogen bonding between DBS and MMA. This was confirmed by Fourier transform infrared (FTIR) spectroscopy and could also explain the differences in the gelation time of the DBS organogels: gels form more slowly in MMA than in St because of the competing interaction, hydrogen bonding, between DBS and MMA. Subsequently, we thermally initiated the free-radical polymerization of these St/MMA co-monomers. PS/PMMA copolymers were obtained, and no macroscopic phase separation occurred after the polymerization. Finally, the porous structures of the polymers produced by the solvent extraction of the DBS templates were observed, using TEM.     

Organoboronium amphiphilic block copolymers

A new class of amphiphilic organometallic block copolymers with cationic organoboron pendant groups was developed. Selective replacement of one of the bromine substitutents on each boryl group of the block copolymer PSBBr₂‐b‐PS with an organometallic reagent ArM (ArM = 2,4,6‐trimethylphenyl copper, 4‐t‐butylphenyltrimethyl tin) followed by treatment with 2,2′‐bipyridine gave the novel block copolymers [ 3Ar ](Br)_n as light yellow solid materials that show good stability in air and moisture and high solubility in most organic solvents. Their structure and composition were confirmed by multinuclear NMR, GPC, and elemental analysis. Highly regular micellar aggregates form in block‐selective solvents (e.g., MeOH, toluene) as demonstrated by ¹H NMR, dynamic light scattering, and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6612–6618, 2009     

功能性两亲嵌段共聚物的研究进展

功能性两亲嵌段共聚物因自身独特的性质而在靶向输送、控制释放、分子识别等领域得到广泛的应用.本文对这类嵌段共聚物的合成方法、其胶束的形成机理、制备形式、表征手段以及一些常见的具有光学活性的两亲嵌段共聚物及其应用进行了综述.     

新型线状-树枝状两亲嵌段共聚物的合成

本文设计合成了一系列由不同链长的聚丙烯酸(PAA)为亲水嵌段和不同代数聚苄醚树枝体(Dendr.PBE)为疏水嵌段的杂化共聚物(PAA-Dendr.PBE)。     

Synthesis and surface properties of amphiphilic block copolymers polyvinylpyrrolidone-block-polystyrene

Amphiphilic block copolymers of N-pyrrolidone and styrene were prepared by chain transfer to organogermanium compounds bis(pentafluorophenyl)germane and tris(pentafluorophenyl)germane. The relative chain-transfer constants were determined. The surface properties of the isolated block copolymers with various numbers of units in the hydrophilic block were studied. The polar and dispersive components of the surface tension of films of the amphiphilic block copolymers were calculated by the Zisman method.     

Synthesis and aggregation behaviour of amphiphilic block copolymers with random middle block

The effect of microstructure on the aggregation behaviour of symmetrical di- and triblock copolymers P(BMA)-b-P(MAA) and P(BMA)-b-P(BMA-co-MAA)-b-P(MAA) with a molecular weight of 40,000 g/mol was studied. The critical micelle concentration, hydrodynamic radius and morphology of the micelles were determined by fluorescence spectroscopy, dynamic light scattering and scanning force microscopy (SFM). Whereas no effect of the microstructure on the critical micelle concentration could be detected, the hydrodynamic radius decreased from di- to triblock copolymer from 53 to 36 nm. The decrease of about 32% corresponds to the length of the random middle block within the triblock copolymer so that the reduction in hydrodynamic radius was caused by a complete orientation of the random middle block at the core corona interface. Finally, the SFM investigation showed that dehydration of micelles on a substrate is accompanied by formation of a physisorbed monolayer with a thickness of 2 nm on which the micelles are deposited.     

Non-ionic amphiphilic block copolymers by RAFT-polymerization and their self-organization

Water-soluble, amphiphilic diblock copolymers were synthesized by reversible addition fragmentation chain transfer polymerization. They consist of poly(butyl acrylate) as hydrophobic block with a low glass transition temperature and three different nonionic water-soluble blocks, namely, the classical hydrophilic block poly(dimethylacrylamide), the strongly hydrophilic poly(acryloyloxyethyl methylsulfoxide), and the thermally sensitive poly(N-acryloylpyrrolidine). Aqueous micellar solutions of the block copolymers were prepared and characterized by static and dynamic light scattering analysis (DLS and SLS). No critical micelle concentration could be detected. The micellization was thermodynamically favored, although kinetically slow, exhibiting a marked dependence on the preparation conditions. The polymers formed micelles with a hydrodynamic diameter from 20 to 100 nm, which were stable upon dilution. The micellar size was correlated with the composition of the block copolymers and their overall molar mass. The micelles formed with the two most hydrophilic blocks were particularly stable upon temperature cycles, whereas the thermally sensitive poly(N-acryloylpyrrolidine) block showed a temperature-induced precipitation. According to combined SLS and DLS analysis, the micelles exhibited an elongated shape such as rods or worms. It should be noted that the block copolymers with the most hydrophilic poly(sulfoxide) block formed inverse micelles in certain organic solvents.     

Synthesizing amphiphilic block copolymers through macromolecular azo-coupling reaction

This communication reports a new approach to synthesize amphiphilic block copolymers. The copolymers with well-defined structures were synthesized by macromolecular azo-coupling reaction between the diazonium salt of aniline-functionalized PEG and the polymeric blocks with a terminal suitable for the azo-coupling reaction.     

Synthesis of amphiphilic block copolymers polystyrene-block-polyvinylpyrrolidone from active polystyrene

A new method was developed for preparing amphiphilic block copolymers polystyrene-block-polyvinylpyrrolidone. The colloid-chemical properties of the copolymers were studied by probe microscopy and wetting. The possibility of modifying the properties of surfaces by the block copolymers synthesized and of preparing inverse emulsions based on them was demonstrated.     

Interactions of amphiphilic block copolymers with lipid model membranes

Studies on interactions between amphiphilic block copolymers and lipid membranes have been focused traditionally on ABA triblock copolymers of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), widely due to their commercial availability. However, new architectures of amphiphilic block copolymer have been synthesized in recent years partially taking advantage of new polymerization techniques. This review focuses on amphiphilic block copolymers with potential biological activity and on model membrane systems used for studying interactions with such block copolymers. Experimental methods to study block copolymer–phospholipid interactions in Langmuir monolayers, liposomes, and planar bilayers are summarized. This work is intended to convey a better understanding of amphiphilic block copolymers used for in vitro and in vivo experiments in medicine and pharmacy. Recent developments and open questions are addressed.     

Synthesis of amphiphilic block copolymers bearing stable nitroxyl radicals

We present here the synthesis of two kinds of amphiphilic block copolymers, a diblock copolymer MPEG‐b‐PTAm and a triblock copolymer MPEG‐b‐PLA‐b‐PTAm, which can self‐assemble into micelles with nitroxyl radicals‐containing PTAm segment in the core. The structure of the block copolymers was characterized by ¹H NMR and GPC. Dynamic laser light scattering and transmission electron microscopy were used to study the micellar behavior of the two block copolymers in aqueous solution. The micelles carrying nitroxyl radicals in the core can generate electron paramagnetic resonance, which is stable for a period of time up to 8 min even in the presence of reducing reagent such as ascorbic acid. The enhanced stability against the reducing agent was ascribed to the inaccessibility of the nitroxyl radical core placed in the interior of the micelles. Combined with the biocompatibility, these micelles were promising to be used as the EPR probes for bioimaging in vivo. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Novel fluorescent amphiphilic block copolymers: Controllable morphologies and size by self-assembly

New fluorescent amphiphilic copolymers polyacrylamide-b-poly(p-methacrylamido)acetophenone thiosemicarbazone (PAM-b-PMATC) were synthesized by atom transfer radical polymerization (ATRP) method. The structures of polymers were confirmed by ¹H NMR and gel permeation chromatography-multi-angle laser light scatting (GPC-MALLS). PAM-b-PMATC showed a broad emission peak about 388 nm excited at 318 nm in aqueous solution. The self-assembly behavior of PAM-b-PMATC in the binary mixture formamide/water was observed by transmission electron microscope (TEM). It indicated that PAM-b-PMATC-I and -II with the same PAM block self-assembled to vesicles and sunflower-like micelles. The water fraction in the mixture could control the size and thickness of vesicles. Vesicle size increased from 50 to 420 nm and vesicle thickness changed from 5 to 50 nm with water content ranging from 33 to 90 vol.%. In addition, the cytotoxicity in vitro of PAM-b-PMATC-I and its nanoparticles loaded with methotrexate (MTX) were evaluated by MTT assay.     

Foam and wetting films from amphiphilic block copolymers: Isoelectric state and stability

Foam and wetting films from PEO-PPO-PEO triblock copolymers Synperonic P85 and F108 are studied under the identical conditions, using microinterference method. The range of background electrolyte concentration, where DLVO (electrostatic and van der Waals) forces and non-DLVO (steric) forces act in the films, is determined. From the dependence of the film thickness on pH, it is unambiguously shown that electrostatic interactions (i.e., the potential and surface charge) in the foam and wetting films caused by the presence of nonionic polymer surfactants arise due to the preferential adsorption of OH⁻ ions at the solution-air interface. The films obtained below the critical pH values are sterically stabilized; i.e., a decrease in pH induces a transition from electrostatic to steric stabilization. Three-layer models are designed for both types of films that allow to calculate electrostatic disjoining pressure Π_el. The values of ϕ₀ potential of the foam film are used to calculate Π_el in wetting films. A relation between the isoelectric state of foam and wetting films and their stability is found to exist in the range of pH corresponding to electrostatic stabilization. Metastable films, film rupture, or the transition to sterically stabilized films were also found. The text was submitted by the authors in English.     

Formation of polymer vesicles by liquid crystal amphiphilic block copolymers

We report the formation of polymer vesicles (or polymersomes) by a new class of amphiphilic block copolymers in which the hydrophobic block is a side-on nematic liquid crystal polymer. Two series of these block copolymers, named PEG-b-PA444 and PEG-b-PMAazo444, with different hydrophilic/hydrophobic ratios were synthesized and characterized in detail. Polymersomes and nanotubes were formed by adding water into a solution of copolymers in dioxane. Polymersomes in water were finally obtained by dialyzing the resulting mixture against water. These self-assemblies have been studied by classical TEM and cryo-TEM. For the PEG-b-PA444 series, polymersomes were observed for hydrophilic/hydrophobic ratios ranging from 40/60 to 19/81. For PEG-b-PMAazo444 series, polymersomes were observed for hydrophilic/hydrophobic ratios ranging from 26/74 to 18/82. For a PEG-b-PA444 sample with hydrophilic/hydrophobic ratio equal to 25/75, a tubular morphology with tube diameter of typically 100 nm and tube length of up to 10 mum was also observed together with polymersomes during addition of water into the polymer solution in dioxane.     

Syntheses of amphiphilic block copolymers. Block copolymers of methacrylic acid and p-N,N-dimethylaminostyrene

Amphiphilic block copolymers consisting of methacrylic acid (MA) sequences and p-N,N-dimethylaminostyrene (DMS) sequences were prepared by living anionic polymerization. DMS was polymerized by lithium naphthalene in tetrahydrofuran to yield a living polymer solution, to which trimethylsilyl methacrylate (TMSM) was added to allow the block copolymerization. The conversion of TMSM was dependent on the countercation, i.e., with Na⁺ as counterion, no quantitative conversion was reached owing to premature termination, whereas with Li⁺ the conversion was quantitative. The role of the counterion was discussed in some detail in connection with self-termination by the backbiting mechanism. The trimethylsilyl ester groups in the block copolymer were quantitatively hydrolyzed by treatment with aqueous methanol at room temperature, yielding MA sequences. The block copolymer of MA and DMS exhibited micellar properties in an aqueous solution.     

Anti-biofouling properties of comblike block copolymers with amphiphilic side chains

Surfaces of novel block copolymers with amphiphilic side chains were studied for their ability to influence the adhesion of marine organisms. The surface-active polymer, obtained by grafting fluorinated molecules with hydrophobic and hydrophilic blocks to a block copolymer precursor, showed interesting bioadhesion properties. Two different algal species, one of which adhered strongly to hydrophobic surfaces, and the other, to hydrophilic surfaces, showed notably weak adhesion to the amphiphilic surfaces. Both organisms are known to secrete adhesive macromolecules, with apparently different wetting characteristics, to attach to underwater surfaces. The ability of the amphiphilic surface to undergo an environment-dependent transformation in surface chemistry when in contact with the extracellular polymeric substances is a possible reason for its antifouling nature. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) was used, in a new approach based on angle-resolved X-ray photoelectron spectroscopy (XPS), to determine the variation in chemical composition within the top few nanometers of the surface and also to study the surface segregation of the amphiphilic block. A mathematical model to extract depth-profile information from the normalized NEXAFS partial electron yield is developed.     

Sorption of anionic amphiphilic block copolymers by a network polycation

The interaction of amphiphilic block copolymers comprising an anionic block (polyacrylate or polymethacrylate) and a hydrophobic block (polystyrene, poly(butyl acrylate) or polyisobutylene) with lightly crosslinked poly(N,N-diallyl-N,N-dimethylammonium chloride) is studied for the first time. It is shown that the cationic hydrogel can sorb anionic amphiphilic block copolymers via electrostatic interaction with the corona of block copolymer micelles. The rate of sorption of block copolymer polyelectrolytes is significantly lower than the rate of sorption of linear polyions and is controlled by the lengths of the hydrophilic and hydrophobic blocks and the flexibility of the latter blocks. The sorption of amphiphilic block copolymers is accompanied by their self-assembly in the polycomplex gel and formation of a continuous hydrophobic layer impermeable to water and the low-molecular-mass salt dissolved in it.     

Microphase separation in the melts of diblock copolymers composed of linear and amphiphilic blocks

Computer-aided simulation performed via two independent methods (the Monte Carlo method and method of dissipative particle dynamics) is performed for studying the effect of microphase separation in concentrated solutions of diblock copolymers composed of linear blocks A and amphiphilic blocks A-graft-B. The type of microstructures generated by strong incompatibility between units A and B is shown to be controlled by the ratio of block lengths. For example, in the case of short amphiphilic blocks, elongated micelles with correlated mutual alignment are formed. In the case of longer amphiphilic blocks, lamellar structures are produced; with an increase in the length of this block, these structures are transformed into sequences of lamellas containing parallel layers, lamellas with intersecting layers, and perforated lamellas. When the system contains long amphiphilic blocks, bicontinuous structures arise.     

Functionalization of magnetic nanoparticles with amphiphilic block copolymers: self-assembled thermoresponsive submicrometer particles

For the first time the four block copolymers derived from 1-alkyl[2-(acryloyloxy)ethyl]dimethylammonium bromides with hexyl (ADA) or cetyl (ADHA) groups and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) were synthesized and employed for functionalization of monodisperse iron oxide nanoparticles (NPs). The polyADA (pADA) or polyADHA (pADHA) block consists of long hydrophobic tails (C(6) or C(16)) connected to a positively charged quaternary ammonium group, making this block amphiphilic. The second block was either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). The dependence of the NP coating on the length of the hydrophobic tail in the amphiphilic block, the composition of the hydrophilic block, and the NP sizes have been studied. Unusual self-assembling of iron oxide NPs into well-defined composite submicrometer particles was observed for pADHA-b-pNIPAM in the wide range of concentrations (at the pADHA repeating unit concentrations of 0.065 × 10(-2)-2.91 × 10(-2) mmol/mL per 1 mg/mL NPs) but only two concentrations, 1.62 × 10(-2) and 1.94 × 10(-2) mmol/mL, led to regular spherical particles. The thermoresponsive behavior of these composite particles was tested using ζ-potential and dynamic light scattering measurements, while the morphology of particles was characterized by transmission electron microscopy. Coating of NPs with pADHA-b-pHEA results in the formation of individually coated NPs. The different composite particle morphologies are explained by different properties of pHEA and pNIPAM. It is demonstrated that the composite particles based on pADHA-b-pNIPAM are responsive to a magnetic field and can be recommended as magnetic stoppers in biorelated membrane separations. The incorporation of Pd species in submicrometer particles makes them promising candidates for catalytic applications as magnetically recoverable catalysts with a high magnetic response.