Photocrosslinkable smart terpolymers responding to pH,temperature, and ionic strength

A series of copolymers of acrylic acid, N‐isopropylacrylamide (NIPAM), and cinnamoyloxyethyl acrylate were synthesized and studied. The polymers were responsive to four stimuli: UV light, temperature, pH, and ionic strength. The polymeric cinnamoyl chromophores underwent efficient photodimerization with concomitant photocrosslinking of the polymeric micelles. Because of the content of NIPAM, the terpolymers displayed a lower critical solution temperature, which could be controlled by the polymer composition, pH, and ionic strength. The ability to respond to the pH resulted from the content of acrylic carboxyl groups, which became protonated at low pHs. The changes in the polymer properties due to the application of the aforementioned stimuli were studied with pyrene and perylene as fluorescent probes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3879–3886, 2004     

Unusual collapse of highly hydrated polyelectrolyte multilayers with the ionic strength

Highly hydrated polyelectrolyte multilayers (PEMs) were fabricated by “layer by layer” (LBL) assembly of poly (diallyl dimethyl ammonium chloride) (PDADMAC) and poly (sodium 4‐styrene sulfonate) (PSS) in 0.5 M NaCl. Both thickness and hydration of the film were determined in situ as the multilayer was assembled by means of the quartz crystal microbalance with dissipation (QCM‐D) and the Spectroscopic Ellipsometry techniques combined in a single device. For PEMs of 17 total layers in water, a final thickness of up to 300 nm and a hydration of 69% were measured. The response towards the ionic strength was then studied by means of QCM‐D. PEMs of 17 layers, with PDADMAC as last layer, shrunk dramatically and lost water when exposed to aqueous NaCl solutions of increasing concentration. Indeed, a thickness variation up to 100 nm and reduction in the 50% of the water content were observed when the PEM was exposed to 1 M NaCl. On the contrary, PEMs where PSS appears on top showed no measurable change upon the variation in the ionic strength. This brings the possibility to control the responsive character of the PEMs simply by selecting the last polyelectrolyte layer (PDADMAC or PSS) deposited. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Tailor-made polyelectrolyte microcapsules: from multilayers to smart containers

This review addresses the fabrication and properties of novel polyelectrolyte microcapsules, with an emphasis on their mechanical and permeability properties. Ease of preparation through layer-by-layer self assembly, accurate control over wall thickness as well as flexibility in the choice of constituents make these capsules very promising for numerous applications in materials and life science. Moreover, by engineering the inner and outer interfaces, these capsules can be used as microreactors for precipitation, crystallization, and polymerization reactions, as well as enzymatic, and heterogeneous catalysis.     

pH and ionic strength responsive polyelectrolyte block copolymer micelles prepared by ring opening metathesis polymerization

Well‐defined amphiphilic block copolymers were prepared by ring opening metathesis polymerization and their stimuli responsive behavior of formed micelles in aqueous solution was investigated. The hydrophobic core of the micelles consists of either a poly[5,6‐bis(ethoxymethyl)bicyclo[2.2.1]hept‐2‐ene]‐block with a glass transition T_g at room temperature or a poly[endo,exo[2.2.1]bicyclohept‐5‐ene‐2,3‐diylbis (phenylmethanone)] with a T_g of 143 °C. For the polyelectrolyte shell, the precursor block poly[endo,exo[2.2.1]bicyclohept‐5‐ene‐2,3‐dicarboxyclic tert‐butylester] was transformed into the free acidic block by cleavage of the tert‐butyl groups using trifluoroacetic acid. Micellar solutions were prepared by dialysis, dissolving the copolymers in dimethyl sulfoxide which was subsequently replaced by water. All polymers form micelles with radii between 10 and 20 nm at a pH‐value below 5, where the carboxylic acid groups are in the protonated state. The block copolymer micelles show a strong increase of the hydrodynamic radius with increasing pH‐value, due to the repulsion among the formed carboxylate anions resulting in a stretching of the polymer chains. In this state, the micelles exhibit responsive behavior to ionic strength where a contraction of the micelles is observed as the carboxylate charges are balanced by sodium ions, whereas no changes of the hydrodynamic radius on addition of salt are observed at low pH. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1178–1191, 2009     

Role of the preparation procedure in the formation of spherical and monodisperse surfactant/polyelectrolyte complexes

Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed.     

Resealing of Polyelectrolyte Capsules after Core Removal

Poly(styrene sulfonate) and poly(allylamine hydrochloride) layers have been adsorbed supplementarily on polyelectrolyte capsules. The permeability of the original capsules consisting of four layer pairs was of the order of 10^–5 m/s for fluorescein. They were also permeable for macromolecules. Polyelectrolyte layers adsorbed afterwards reduced the permeability by three orders of magnitude for small molecules. These findings are interpreted as a resealing of pores, induced by the osmotic stress during fabrication.     

Equilibrium distribution of permeants in polyelectrolyte microcapsules filled with negatively charged polyelectrolyte: the influence of ionic strength and solvent polarity

The effects of ionic strength and solvent polarity on the equilibrium distribution of fluorescein (FL) and FITC-dextran between the interior of polyelectrolyte multilayer microcapsules filled with negatively charged strong polyelectrolyte and the bulk solution were systematically investigated. A negatively charged strong polyelectrolyte, poly(styrene sulfonate) (PSS), used for CaCO3 core fabrication, was entrapped inside the capsules. Due to the semipermeability of the capsule wall, a Donnan equilibrium between the inner solution within the capsules and the bulk solution was created. The equilibrium distribution of the negatively charged permeants was investigated by means of confocal laser scanning microscopy as a function of ionic strength and solvent polarity. The equilibrium distribution of the negatively charged permeants could be tuned by increasing the bulk ionic strength to decrease the Donnan potential. Decreasing the solvent polarity also could enhance the permeation of FL, which induces a sudden increase of permeation when the ethanol volume fraction was higher than 0.7. This is mainly attributed to the precipitation of PSS. A theoretical model combining the Donnan equilibrium and Manning counterion condensation was employed to discuss the results.     

Multilayer microcapsules as anti-cancer drug delivery vehicle: deposition, Sustained release, and in vitro bioactivity

A drug delivery system based on spontaneous deposition of soluble, low-molecular-weight therapeutic agents has been developed for the purpose of sustaining drug release. Layer-by-layer assembly of oppositely charged polyelectrolytes onto melamine formaldehyde (MF) colloidal particles, followed by removal of the cores at low pH has yielded intact hollow microcapsules having the ability to induce deposition of various water-soluble substances. Dynamic observation by confocal laser scanning microscopy provided direct evidence of such deposition. Dependence of loading rate on molecular weight was investigated. Efficient loading of an anti-cancer drug, daunorubicin (DNR), was confirmed by transmission electron microscopy (TEM). Its release was quantified by fluorometry. The results indicated that loading, and subsequent release, could be tuned by factors such as feeding concentrations, temperature, and salt concentrations. The intrinsic mechanism of loading and release was discussed taking into account the interaction between the drugs and the poly(styrene sulfonate)/MF complex existing in the hollow capsules. With culture of the HL-60 cell line, a kind of human leukemia cell, the presence of DNR-loaded capsules was seen to steadily decrease the cyto-viability. Fluorescence intensity averaged from inside the circles as a function of incubation time.     

Thixotropy of Aqueous Suspensions Containing Mg‐Al Hydrotalcite‐like Compound and Low‐substituted Cationic Starch: Comparison between Oscillatory Shear and Thixotropic Loop Measurements

The rheological properties of aqueous suspensions consisting of positively charged aluminum magnesium hydrotalcite‐like compound (HTlc) and low‐substituted cationic starch (LCS) were investigated. Special emphasis was placed on the thixotropic phenomenon. Thixotropic behavior was investigated by two thixotropic methods: thixotropic loop and oscillatory shear measurements. LCS molecules could be adsorbed onto HTlc particles due to the hydrogen bonding between ether groups or hydroxyl groups of LCS and hydroxyl groups of HTlc. The elastic dynamic response of the HTlc/LCS suspension increased with increasing mass ratio (R) of HTlc and a three‐dimensional network structure could be formed in the suspension with higher R value. The thixotropic type of the HTlc/LCS suspension transformed from negative to positive and then to complex thixotropy when R changed from 0 to 0.5. By comparing between the thixotropic results obtained by thixotropic loop and oscillatory shear measurements, it was validated that the thixotropic loop for the suspension showing complex thixotropy had a crossover point.     

Compression-inhibited pore formation of polyelectrolyte multilayers containing weak polyanions: a scanning force microscopy study.

Morphological changes of poly(acrylic acid)/poly(diallyldimethylammonium chloride) multilayers induced by low pH were investigated by scanning force microscopy. The weakened interaction between the charged polymer chains in the protonation process is believed to be the reason for this variation. Kinetic studies have shown that during protonation phase separation and dissociation of the multilayers took place successively. The compression of the multilayers, however, caused a transition of the multilayers from a rubbery state to a glassy state. As a result, the closely compacted multilayers lost their sensitivity to pH change. An increase of electrostatic and hydrophobic interactions, can decrease the free energy of the multilayers, and stabilize the films. By compression of the multilayers with a rubber stamp having geometric patterns, films with spatially localized pores were produced.     

用纤维素分散ZnAl-LDHs纳米片提高磷吸附性能

为了利用大比表面积性质,将锌铝层状双金属氢氧化物(ZnAl-LDHs)在甲酰胺中剥离,所得纳米片由纤维素稳定即在水溶液中不发生配列。通过XRD、FTIR、SEM、TEM、元素分析、ICP和离子色谱等手段研究了ZnAl-LDHs纳米片与羧甲基纤维素复合体的结构、组成和形貌,并探讨了纳米片的除磷性能。结果表明复合体对磷酸二氢根离子有很高的选择吸附性和较大的吸附量,吸附量最大约为40 mg(P).g-1(LDHs)。     

Preparation of a solution‐processable,nanostructured ionic polyacetylene

Polymerization of a self‐assembled 1‐dodecyl‐3‐propargylimidazolium bromide ionic liquid (IL) yields a nanostructured ionic polyacetylene. A 1:1 aqueous mixture of the amphiphilic IL produces an ordered lyotropic mesophase that adopts a hexagonal perforated lamellar structure. Rh (I)‐mediated polymerization of the assembled mixture yields a hexagonal modulated lamellar structured polymer. FTIR spectroscopy reveals that the polymer was self n‐doped. The polymer was fractioned into three components with the majority product, possessing an intermediate molecular weight that is soluble in polar organic solvents. In methanol, the optical band gap of the main fraction was determined to be 2.38 eV and was nonemissive. The solution‐processable polymer was airbrush sprayed onto glass substrates to give a liquid‐crystalline, lamellar structured semiconductive film (7.02 × 10^?5 S cm^?1). The polymer resisted oxidation (degradation) upon storage in air as monitored by vibrational spectroscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1215–1227     

Red Blood Cell Templated Polyelectrolyte Capsules: A Novel Vehicle for the Stable Encapsulation of DNA and Proteins

Summary: A novel method for the encapsulation of biomacromolecules, such as nucleic acids and proteins, into polyelectrolyte microcapsules is described. Fluorescence‐labelled double‐stranded DNA and human serum albumin (HSA) are used as model substances for encapsulation in hollow microcapsules templated on human erythrocytes. The encapsulation procedure involves an intermediate drying step. The accumulation of DNA and HSA in the capsules is observed by confocal laser scanning microscopy, UV spectroscopy, and fluorimetry. The mechanism of encapsulation is discussed.

Confocal fluorescence microscopy images of encapsulated TRITC‐HSA (left) and dsDNA (right). Inserts demonstrate fluorescence profiles for both compounds.     

Conformational changes of a polyelectrolyte in mixtures of water and acetone

Samples of a polyelectrolyte poly(methacryloylethyl trimethylammonium methylsulfate), PMETMMS, with molar masses M_w = 22−25 × 10⁶ were examined with viscosity, static light scattering, and conductivity measurements in a water–acetone solvent. Because acetone is a nonsolvent for this polymer the measurements were performed to determine the influence of the solvent composition, the polymer concentration, and the presence of added ions on the conformation of the polyelectrolyte in mixed solvents. The possible influence of a hydrodynamic field on the polymer conformation was also studied. The viscosity of the polymer solutions as a function of polymer concentration, as well as of the solvent composition, was studied using a broad range of shear rates. When the mass fraction of acetone in the solvent, γ, is below 0.5, the solutions show a usual polyelectrolyte behavior. When γ ≥ 0.80, the polymer adopts a compact conformation. This is observed as a decrease of the radius of gyration, R_g, second virial coefficient, A₂, the viscosity, and also as a change in the conductivity of the solution. The change in the polymer conformation may be induced also by dilution. When 0.60 ≤ γ < 0.80, a gradual decrease in the polymer concentration leads to a sudden decrease of the reduced viscosity, which indicates a decrease in the particle size. The values of M_w measured by static light scattering were constant in all experiments. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1107–1114, 1998