Templated synthesis of silver nanoparticles in amphiphilic poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) comb copolymer

In this study, poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐graft‐poly(oxyethylene methacrylate), P(VDF‐co‐CTFE)‐g‐POEM, an amphiphilic comb copolymer with hydrophobic P(VDF‐co‐CTFE) backbone and hydrophilic POEM side chains at 73:27 wt % was synthesized. The POEM side chains were grafted from the P(VDF‐co‐CTFE) mainchain backbone via atom transfer radical polymerization (ATRP) using direct initiation of the chlorine atoms in CTFE units. Synthesis of microphase‐separated P(VDF‐co‐CTFE)‐g‐POEM comb copolymer was successful, as confirmed by nuclear magnetic resonance (¹H NMR), FTIR spectroscopy, and transmission electron microscopy (TEM). Nanocomposite films were prepared using the comb copolymer as a template film and the in situ reduction of AgCF₃SO₃ precursor to silver nanoparticles under UV irradiation. Silver nanoparticles with 4–8 nm in average size were in situ created in the solid state template film, as revealed by TEM, UV–visible spectroscopy, and wide angle X‐ray scattering (WAXS). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) presented the selective incorporation and the in situ growth of silver nanoparticles within the hydrophilic POEM domains of microphase‐separated comb copolymer film. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 702–709, 2008     

Reversible activation of diblock copolymer monolayers at the interface by pH modulation, 1: Lateral chain density and conformation

This study focuses on the design of chemically regulated surfaces that allow for reversible control of the interactions between biological matter (cells and proteins) and planar substrates. As a tunable interlayer, we use a monolayer of a near-monodisperse poly[2-(dimethylamino)ethyl methacrylate-block-methyl methacrylate] (PDMAEMA-PMMA) diblock copolymer. Owing to the relatively large fraction (50%) of the hydrophobic PMMA block, this copolymer forms a stable Langmuir monolayer at the air/water interface. Both in situ and ex situ film balance experiments suggest that the hydrophilic PDMAEMA block adsorbs to the air/water interface in its uncharged state (pH 8.5), but stretches into the subphase in its charged state (pH 5.5). Optimization of the preparation protocols enables us to fabricate stable, homogeneous diblock copolymer films on hydrophobized substrates via Langmuir-Schaefer transfer at well-defined lateral chain densities. Ellipsometry and X-ray reflectivity studies of the transferred films confirm that the film thickness can be systematically regulated by the lateral chain densities. The transferred copolymer films remain stable in water for about a week, suggesting that they are promising materials for the creation of pH-controlled solid substrates for the support of biological matter such as proteins and cells.     

pH sensor based on polyaniline and aniline–anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopy

The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o‐anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV–Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2–12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25 M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV–Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pK_a for both films. Copyright © 2008 John Wiley & Sons, Ltd.     

Antifouling ultrafiltration membrane composed of polyethersulfone and sulfobetaine copolymer

A new random copolymer was synthesized by reacting hydrophilic N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) (DMMSA) with hydrophobic butyl methacrylate (BMA) through a conventional radical polymerization. The as-prepared sulfobetaine copolymer (DMMSA–BMA) was blended with polyethersulfone (PES) to fabricate antifouling ultrafiltration membrane for BSA separation. The X-ray photoelectron spectroscopy analysis of blend membranes revealed concentration of sulfobetaine groups at the membrane surfaces that endowed the membrane with higher hydrophilicity and better antifouling property. For the membrane with 8.0 wt% DMMSA–BMA copolymer concentration (No. 5), irreversible fouling has been considerably reduced and the flux recovery rate of the blend membrane reached as high as 82.8%. Furthermore, the blend membrane could effectively resist BSA fouling in a wide pH range from 4.0 to 8.0.     

Preparation and Electrochemical Behaviors of AA-PEGMA Copolymer Film Electrode

A new kind of comblike copolymer film composed of acrylic acid-polyethylene glycol monomethyl ether acrylate copolymer(AA-PEGMA copolymer) was successfully synthesized to immobilize hemoglobin(Hb). FTIR, UV-Vis and CD spectra suggest that Hb kept its original structure in the AA-PEGMA copolymer film without denaturation. A pair of well-defined, quasi-reversible cyclic voltammetric peaks at around –270 mV vs. saturated calomel electrode(SCE) for the Hb Fe(Ⅲ)/Fe(Ⅱ) redox couple was observed on the film-modified electrode in phosphate buffer solution(PBS, pH=7.0). The formal potential of Hb/AA-PEGMA copolymer film-modified electrode is linearly dependent on solution pH with a slope of –46.3 mV/pH, illustrating that one-proton transfer was accompanied with each electron transfer. Furthermore, the modified electrode displayed electrocatalytic response to the reduction of H₂O₂ with a linear range of 3.5―126 μmol/L and a detection limit of 1.17 μmol/L. In conclusion, the AA-PEGMA copolymer film was proved to be an excellent matrix for the immobilization and electrochemistry of proteins.     

聚乙二醇-b-聚对苯二甲酸丁二醇酯嵌段共聚物降解行为的研究

研究了系列PEG-b-PBT嵌段共聚物在pH=7.4磷酸盐缓冲溶液中和37℃条件下的体外降解行为.同时观察了水解降解过程中系列共聚物溶胀率、失重、特性粘度、结晶度和表面形态等方面的变化.实验结果表明,嵌段共聚物的组成直接影响其水解降解性能,共聚物的溶胀率和失重率随聚醚组分含量而增大;通过调节共聚物的组分比可以达到调节降解速率的目的.此外研究还表明,共聚物最初的降解主要发生在软段和硬段相联的酯键上.     

pH-Responsive Self-assembled Nanoparticles of Simulated P(AA-co-SA)-g-PEG for Drug Release

Simulated graft copolymer of poly(acrylic acid-co-stearyl acylate) [P(AA-co-SA)] and poly(ethylene glycol) (PEG) was synthesized, where acrylic acid, stearyl acylate and PEG was employed as the pH-sensitive, hydrophobic and hydrophilic segment, respectively. Polymeric nanoparticles prepared by the dialysis of simulated graft copolymer solution in dimethylformamide against citrate buffer solution with different pH values were characterized by transmission electron microscopy (TEM), fluorescence technique and laser light scattering (LLS). TEM image revealed the spherical shape of the self-aggregates, which was further confirmed by LLS measurements. The critical aggregation concentration increased markedly (10 to 150 mg/L) with increasing pH (4.6 to 7.0), consistent with the de-protonation of carboxylic groups at higher pH. The hydrodynamic radius of polymeric nanoparticles decreased from 118 nm at pH 3.4 to 90 nm at pH 7.0. The controlled release of indomethacin from those nanoparticles was investigated, and the self-assembled nanoparticles exhibited improved performance in controlled drug release.     

Research of the relationship of intracellular acidification and apoptosis in Hela cells based on pH nanosensors

In this paper,the relationship of intracellular acidification and apoptosis in Hela cells induced by vin-cristine sulfate has been studied by use of the ratiometric pH nanosensors that have been developed by our group,employing fluorescein isothiocyanate(FITC) doped as the pH-sensitive dye and Tris(2,2'-bipyidyl) dichlororuthenium(II) hexahydrate(RuBpy) doped as reference dye. The pH change of the Hela cells induced by vincristine sulfate has been monitored in vivo,in situ and real time by use of the ratiometric pH nanosensors. The experimental results show that the pH of the apoptotic Hela cells induced by vincristine sulfate has been acidified from 7.11 to 6.51,and the percentage of intra-cellular acidification is correlated with the induced concentration and incubation time of the vincristine sulfate. The further study of the percentage of intracellular acidification and the percentage of apop-tosis of Hela cells at the same time reveals that apoptosis of Hela cells induced by vincristine sulfate is preceded by intracellular acidification. These results would provide theoretical foundation for the therapy of cancer through interfering the pH of cells by use of vincristine sulfate or other anti-cancer drugs.     

Double‐hydrophilic block copolymer for encapsulation and two‐way pH change‐induced release of metalloporphyrins

A double hydrophilic block copolymer composed of poly(acrylic acid) (PAA) and poly(4‐vinyl pyridine) (P4VP) was obtained through hydrolysis of diblock copolymer of poly(tert‐butyl acrylate) (PtBA) and P4VP synthesized using atom transfer radical polymerization. Water‐soluble micelles with PAA core and P4VP corona were observed at low (acidic) pH, while micelles with P4VP core and PAA corona were formed at high (basic) pH. Two metalloporphyrins, zinc tetraphenylporphyrin (ZnTPP) and cobalt tetraphenylporphyrin (CoTPP), were used as model compounds to investigate the encapsulation of hydrophobic molecules by both types of micelles. UV–vis spectroscopic measurements indicate that micelles with P4VP core are able to entrap more ZnTPP and CoTPP as a result of the axial coordination between the transition metals and the pyridine groups. The study found that metalloporphyrins encapsulated by the micelles with PAA core could be released on pH increase, while those entrapped by the micelles with P4VP core could be released on pH decrease. This behavior originates from the two‐way pH change‐induced disruption of PAA‐b‐P4VP micelles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1734–1744, 2006     

聚苯乙烯-聚(4-乙烯基吡啶)嵌段共聚物LB膜结构形态的研究

采用氯仿作为铺展溶剂,将嵌段共聚物聚苯乙烯-聚(4-乙烯基吡啶)(PS-b-P4VP)稀溶液铺展于空气与水界面上,利用Langmuir-Blodgett(LB)膜技术转移至固体基底.研究了不同的嵌段比、表面压和小分子1-芘丁酸(PBA)的加入对嵌段共聚物气液界面聚集组装的影响.研究发现随着亲水段(P4VP)的增加,聚集组装结构由纳米片状、带状转变成纳米条状、纳米点状结构.表面压对纯PS-b-P4VP聚集组装产生影响,表面压增大,组装体排列紧密;随着表面压的继续增大,单层聚集结构遭到破坏,发生堆叠.加入PBA小分子后,PBA与PS-b-P4VP形成氢键,形态发生明显变化,原来的片状结构转变为条状或点状结构.     

Improved surface properties of polyaniline films by blending with Pluronic polymers without the modification of the other characteristics

Films of conductive polyaniline and amphiphilic Pluronic (P105) copolymer blends were prepared by dissolving the two polymers in N-methylpyrrolidinone (NMP) followed by a slow solvent evaporation at 55 degrees C. The characteristics of both doped and undoped films were determined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), water droplet contact angles, differential scanning calorimetry (DSC), thermal gravimetry analysis (TG), wide-angle X-ray diffraction (WAXD), and tensile strength measurements. The surface of the blends became more hydrophilic than that of the hydrophobic PANI film, but the other properties of the blends did not change appreciably for Pluronic content lower than 50 wt%. Compared to PANI films, the more hydrophilic surfaces decreased the amount of bovine serum albumin protein adsorbed. By preventing biofouling, the polyaniline-Pluronic blends can become more useful as biosensors than the polyaniline films.     

Synthesis and characterization of thermally crosslinked polyimide with second-order nonlinear optical chromophore

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Synthesis, rapid responsive thickening, and self-assembly of brush copolymer poly(ethylene oxide)-graft-poly(N,N-dimethylaminoethyl methacrylate) in aqueous solutions

Double hydrophilic brush copolymer poly(ethylene oxide)-graft-poly(N,N-dimethylaminoethyl methacrylate) (PEO-g-PDMAEMA) was successfully prepared via atom transfer radical polymerization (ATRP). We investigated the pH/thermoresponsive behaviors of PEO-g-PDMAEMA brush-shaped copolymer concentrated aqueous solutions by rheology. The observed LCST strongly decreased with increasing pH of the solutions, which was lower than that of linear block copolymer for different pH, indicating rapid thermoresponsiveness of the brush PDMAEMA chains. An unexpected shear thickening behavior was observed and could be tuned by the pH, resulting from the mobile nature and tractive force of the densely grafted hydrophobic chains of PDMAEMA at high pH. Self-assembly of the brush copolymer in a different pH and ionic strength environment was studied by transmission electron microscopy. A wormlike cylinder structure was formed at low pH. Fractals were observed for the brush copolymer aqueous solution in the presence of NaCl. The results showed that by adjusting the pH and NaCl concentration of the dispersions fractal aggregates with different topology were obtained. The observations reported here can supply a better understanding of the molecular self-assembling nature and be used to develop responsive materials with better performance.     

pH-responsive copolymer films by surface-catalyzed growth

We have engineered a new class of pH-responsive polymer films on gold surfaces by first developing a controlled, surface-catalyzed polymerization to prepare a copolymer film consistent with poly(methylene-co-ethyl acetate) and subsequently hydrolyzing the ester side chains to varying extents to yield carboxylic acids (denoted as PM-CO2H). When pH is increased, the acid groups become deprotonated or charged, dramatically increasing their water solubility and greatly altering the film properties. The carboxylic acid content within the copolymer film can be adjusted by changing the monomer concentration ratio used in the polymerization process or the length of time for the hydrolysis. We have designed PM-CO2H films to consist predominately (>95%) of polymethylene (PM) so that the film is hydrophobic in the uncharged state and, thereby, exhibits an extremely large pH-induced response in barrier properties once ionized. The effect of polymer composition on pH response was investigated by electrochemical impedance spectroscopy (EIS), reflectance-absorption infrared spectroscopy (RAIRS), and contact angle measurements. At a 1%-4% molar acid content, the copolymer film exhibits a 5 orders of magnitude change in its resistance to ion transport over 2-3 pH units. The pH at which this response begins can be tailored from pH 5 to pH 10 by decreasing the acid content in the film from 4% to 1%.     

Composition and solution properties of fluorinated block copolymers and their surface structures in the solid state

A series of diblock copolymers composed of methyl methacrylate and 2-perfluorooctylethyl methacrylate (PMMA₁₄₄-b-PFMA _n ) with various PFMA block lengths were prepared by atom transfer radical polymerization (ATRP). The surface structures and properties of these polymers in the solid state and in solution were investigated using contact angle measurement, X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, surface tension and dynamic laser light scattering (DLS). It was found that with increasing PFMA block length, water and oil repellency decreased, the ratio of F/C increased with increasing film depth, and the degree of ordered packing of the perfluoroalkyl side chains at the surface decreased. When the number of PFMA block units reached 10, PMMA segments were detected at the copolymer surface, which was attributed to the PFMA block length affecting molecular aggregation structure of the copolymer in the solution and the interfacial structure at the air/liquid interface, which in turn affects surface structure formation during solution solidification. The results suggest that copolymer solution properties play an important role in structure formation on the solid surface. Supported by the National Natural Science Foundation of China (Grant Nos. 50573069 and 20704038) and Program for Changjiang Scholars and Innovative Research Team in University (Grant No.IRT 0654)     

Swelling–shrinking behavior of hydrated noncross‐linked copolymer films in response to photoreversible isomerizaton and metal complexation of spiropyran units of the copolymers

The copolymer of hydroxypropyl methacrylate (HPMA) and photochromic spiropyran methacrylate (SPMA) has been synthesized. The films of the copolymer (P(HPMA‐SPMA)) in a hydrated state showed reversible swelling–shrinking behavior in response to photoreversible isomerization and metal complexation of SPMA units in spite of covalently noncross‐linked copolymers. In addition, the protonated open form of the SPMA units of the copolymer was possibly stabilized thermodynamically by the HPMA units from ultraviolet–visible absorption measurement of the hydrated P(HPMA‐SPMA) film. On the other hand, the difference in color of the hydrated films between P(HPMA‐AABMA) and P(NIPMA‐AABMA), which was a copolymer of N‐isopropyl methacryl amide (NIPMA) and azobenzene methacrylate (AABMA) as a pH indicator, was suggestive of the interference of the proximal hydroxyl groups of the immobilized HPMA units with protonation of the AABMA units. The HPMA units of the copolymers also contributed to improvement of thermodynamic stability of the metal complexes with the SPMA units. Copyright © 2013 John Wiley & Sons, Ltd.     

Polymeric nanoparticles prepared using salt bridges between [(dimethylamino)propyl]-octadecanamide and poly(N-isopropylacrylamide-co-methacrylic acid)

Polymeric lipid nanoparticles were prepared in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH 8.0, 10 mM) by taking advantage of salt bridges formed between poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) and N-[3-(dimethylamino)propyl]-octadecanamide (DMAPODA). The homogeneous nanoparticles of 200–250 nm were obtained when the copolymer was included in the preparation so that the relative mass of copolymer to lipid was more than 5. However, when the relative amount of copolymer was less than 5, large agglomerates more than 10 μm were observed together with nanoparticles. The protonated amino groups of DMAPODA will attach to the ionized carboxyl groups of P(NIPAM-co-MAA), and they would act as polymeric amphiphiles. It is believed that the hydrophilic copolymer can stabilize the hydrophobic core of the lipid. The critical association concentrations were determined to be 32, 112, and 158 mg/l, when the lipid/copolymer ratios were 1:5, 1:23, and 1:50, respectively.     

Participation of electrolyte cations in albumin adsorption onto negatively charged polymer latices

The participation of electrolyte cations in the adsorption of bovine serum albumin (BSA) onto polymer latices was investigated. The latices used were hydrophobic polystyrene (PS), and hydrophilic copolymers, i.e., styrene (St)/2-hydroxyethyl methacrylate(HEMA) copolymer [P(St/HEMA)] and styrene/acrylamide (AAm) copolymer [P(St/AAm)]. Three kinds of electrolyte cations (Na⁺, Ca²⁺, Mg²⁺) were used as the chloride. The amount of BSA adsorbed in every cation medium showed a maximum near the isoelectric point (iep, pH about 5) of the protein. The amounts of BSA adsorbed onto copolymer latices (except in the acidic pH region lower than the iep) were considerably smaller than that onto PS latex because of the steric repulsion and the decrease in the hydrophobic interaction between BSA and copolymer latices. In the acidic pH region, there was little difference in the amount of BSA adsorbed in every cation medium. However, in the pH region higher than the iep, the amounts of BSA adsorbed (particularly onto PS latex) in divalent cations (Ca²⁺ and Mg²⁺) media were relatively greater compared with that in a monovalent (Na⁺) one. This result was interpreted on the basis of the differences in such effects of electrolyte cations as dehydration power, suppression of the electrostatic repulsion, and binding affinity to BSA molecule. Ion Chromatographic estimation of the amounts of electrolyte cations captured upon BSA adsorption (in pH > 5) revealed that divalent cations were incorporated into the contact interface between the latex and BSA molecule so as to prevent the accumulation of anion charge and facilitate the protein adsorption.     

ROD-LIKE AGGREGATES FROM POLYSTYRENE-b-POLY(4-VINYLPYRIDINE)-b-POLYSTYRENE TRIBLOCK COPOLYMER IN AQUEOUS MEDIA

INTRODUCTIONRecently, solution-state assembly of block copolymers has attracted much interest. On the one hand, theversatility of morphology control can be used for the preparation of unique nanostructured materials with variousarchitectures[1-8]. On the other hand, some self-assembled structures are biomimetic[9,10]. The balance betweenthree major forces acting on the system affects block copolymer morphologies in solutions[11,12]. These threeforces include the stretching of the core-for…     

Synthesis of double hydrophilic graft copolymer containing poly(ethylene glycol) and poly(methacrylic acid) side chains via successive ATRP

A well‐defined double hydrophilic graft copolymer, with polyacrylate as backbone, hydrophilic poly(ethylene glycol) and poly(methacrylic acid) as side chains, was synthesized via successive atom transfer radical polymerization followed by the selective hydrolysis of poly(methoxymethyl methacrylate) side chains. The grafting‐through strategy was first used to prepare poly[poly(ethylene glycol) methyl ether acrylate] comb copolymer. The obtained comb copolymer was transformed into macroinitiator by reacting with lithium diisopropylamine and 2‐bromopropionyl chloride. Afterwards, grafting‐from route was employed for the synthesis of poly[poly(ethylene glycol) methyl ether acrylate]‐g‐poly(methoxymethyl methacrylate) amphiphilic graft copolymer. The molecular weight distribution of this amphiphilic graft copolymer was narrow. Poly(methoxymethyl methacrylate) side chains were connected to polyacrylate backbone through stable C? C bonds instead of ester connections. The final product, poly[poly(ethylene glycol) methyl ether acrylate]‐g‐poly(methacrylate acid), was obtained by selective hydrolysis of poly(methoxymethyl methacrylate) side chains under mild conditions without affecting the polyacrylate backbone. This double hydrophilic graft copolymer was found be stimuli‐responsive to pH and ionic strength. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4056–4069, 2008