Double-polyelectrolyte, like-charged amphiphilic diblock copolymers: swollen structures and pH- and salt-dependent lyotropic behavior

We consider a symmetrical poly(styrene- stat-(acrylic acid))- block-poly(acrylic acid), i.e., PSAA- b-PAA, diblock copolymer, with a molar fraction phi AA = 0.42 of acrylic acid, in the more hydrophobic PSAA statistical first block. We investigate its structural behavior at constant concentration in water using small-angle neutron scattering (SANS) by varying (i) the ionization of its acrylic acid motives via the pH by adding NaOH and (ii) the ionic strength of the solution by increasing the NaCl salt concentration c S. We present the resulting morphological phase diagram {pH, c S}, in which we identified two different lamellar phases presenting a smectic long-range order at small-to-intermediate ionizations and a spherical phase with a liquid-like short-range order at larger ionization. In the low-ionization regime, the first lamellar phase comprises a water-free PSAA lamellar core surrounded by a dense poly(acrylic acid) brush swollen with water. Its mostly hydrophobic core still being glassy, this phase is unable to reorganize and is frozen in. A detailed analysis of the SANS data shows the osmotic nature of the polyelectrolyte brush, in which the Na+ counterions are confined so that local electroneutrality is satisfied. Above the pH at which the PSAA statistical block starts ionizing, the PSAA lamellar core melts. The second lamellar phase identified then comprises a PSAA core thinner than that of the frozen-in previous phase, implying a significant increase of the core/water interface and a decrease of the brush surface density. The transition from the first lamellar phase to the second one can be quantitatively shown to result from the balance between the two contributions: (i) the extra interfacial cost between the thinner core and water and (ii) the associated gain in entropy of mixing for the counterions confined inside the brush. At even higher ionization, the diblocks finally form spherical objects with a very small, pH-dependent aggregation number and reach an apparent onset of self-association. When the highest ionization investigated is reached, the cores of these final spherical core-shell objects are found to contain a significant amount of water. We thereby demonstrate that at constant concentration, pH, and ionic strength both trigger a transition from frozen to molten hydrophobic phases as well as unexpected morphological transitions.     

Unique toroidal morphology from composition and sequence control of triblock copolymers

The mechanism by which the unique toroidal supramolecular assemblies were formed for triblock copolymers of acrylic acid (AA), methyl acrylate (MA), and styrene (S), PAA99-b-PMA73-b-PS66, was probed in this study by investigating the influences of the block copolymer compositions and sequences. Two triblock copolymers, PAA99-b-PMA73-b-PS66 and PAA99-b-PS76-b-PMA62, and two diblock copolymers, PAA99-b-PMA155 and PAA99-b-PS133, were studied under experimental solution-state conditions that involved a range of solvent/nonsolvent (tetrahydrofuran/water) compositions, each in the presence of 2,2'-(ethylenedioxy)bis(ethylamine). The resulting morphologies were determined by transmission electron microscopy. The failures to afford toroidal supramolecular assemblies from both diblock copolymers having comparable lengths of the total hydrophobic chain segment, either entirely PMA or entirely PS, and from the triblock copolymer having a reversed connection sequence for the hydrophobic (PMA and PS) segments demonstrate the unique self-assembly behaviors of triblock copolymers and the importance of the block copolymer sequence.     

Nanosized amorphous calcium carbonate stabilized by poly(ethylene oxide)-b-poly(acrylic acid) block copolymers

Particles of amorphous calcium carbonate (ACC), formed in situ from calcium chloride by the slow release of carbon dioxide by alkaline hydrolysis of dimethyl carbonate in water, are stabilized against coalescence in the presence of very small amounts of double hydrophilic block copolymers (DHBCs) composed of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) blocks. Under optimized conditions, spherical particles of ACC with diameters less than 100 nm and narrow size distribution are obtained at a concentration of only 3 ppm of PEO-b-PAA as additive. Equivalent triblock or star DHBCs are compared to diblock copolymers. The results are interpreted assuming an interaction of the PAA blocks with the surface of the liquid droplets of the concentrated CaCO3 phase, formed by phase separation from the initially homogeneous reaction mixture. The adsorption layer of the block copolymer protects the liquid precursor of ACC from coalescence and/or coagulation.     

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     

全亲水丙烯酰胺/丙烯酸类梳型聚合物的合成及双重响应性聚集行为

以引发剂量的壳聚糖 (CS)为母体骨架,通过与丙烯酰胺 (AM)和丙烯酸 (AA)连续的自由基聚合反应,制备了一种全亲水丙烯酰胺/丙烯酸类梳型聚合物 (CS-PAM/PAA).聚合物中丙烯酰胺和丙烯酸的组成比例可通过控制反应时间调节,并可通过核磁共振碳谱定量计算.该聚合物具有全亲水嵌段共聚物的特性,在水溶液中具有良好的pH响应性和离子响应性.聚合物溶于水并在酸性条件下自组装形成囊泡结构的聚集体,多价金属离子(如Tb³⁺离子)也可以引起聚合物的响应聚集.     

Stimuli-responsive polyelectrolyte block copolymer brushes synthesized from the Si wafer via atom-transfer radical polymerization

Surface-tethered oppositely charged weak polyelectrolyte block copolymer brushes composed of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) were grown from the Si wafer by atom-transfer radical polymerization. The P2VP-b-PAA brushes were prepared through hydrolysis of the second PtBA block to the corresponding acrylic acid. The P2VP-b-PAA brushes with different PAA block length were obtained. The P2VP-b-PAA brushes revealed a unique reversible wetting behavior with pH. The difference between the solubility parameters for P2VP and PAA, the changes of surface chemical composition and surface roughness, and the reversible wetting behavior illustrated that the surface rearrangement occurred during treatment of the P2VP-b-PAA brushes by aqueous solution with different pH value. The reversible properties of the P2VP-b-PAA brushes can be used to regulate the adsorption of the sulfonated PS nanoparticles.     

Synthesis and solution properties of anionic linear–dendritic block amphiphiles

The design and synthesis of novel linear–dendritic diblock amphiphiles with linear poly(acrylic acid) (PAA) as the hydrophilic block and dendritic poly(benzyl ether) as the hydrophobic block are described. The synthetic process consisted of two steps: a poly(methyl acrylate) (PMA)–poly(benzyl ether) dendrimer series were synthesized with atom transfer radical polymerization, and through the hydrolysis of linear PMA block into PAA, amphiphilic block copolymers, the PAA–poly(benzyl ether) dendrimer series, were obtained. The copolymers were characterized by ¹H NMR, Fourier transform infrared, and size exclusion chromatography and exhibited well‐defined architectures and low polydispersities. When the generation number of the dendritic block (G_i) less or equal to 3 and the degree of polymerization of the linear chain (n) was greater than 10, the amphiphiles were water‐soluble. The solution intrinsic viscosity increased with both the length of linear chain and the generation number of the dendritic block. The results obtained demonstrate that dendritic blocks play an unusual role in aqueous solutions of amphiphiles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4282–4288, 2000     

3种丙烯酸系列高吸水树脂的吸水性能

采用反相悬浮聚合法合成了3种聚丙烯酸系列吸水树脂：聚丙烯酸钠(PAA)、丙烯酸-丙烯酰胺共聚物(P(AA/AM))和丙烯酸-马来酸酐共聚物(P(AA/MA))。 对3种树脂的吸水性、保水性、耐候性和耐电解质等性能进行测试比较。 结果表明,P(AA/MA)的吸水性能最优异,10 min内吸蒸馏水量可达3578.4 g/g;在一定的温度或压力范围内,3种树脂均有良好的保水性能,在不同温度下储存均能保持各自的吸水性;P(AA/MA)的耐电解质性能较为突出,吸生理盐水量可达107.2 g/g,其综合性能最好。     

Hydrogen bond mediated self-assembly of two diblock copolymers

Two chemically dissimilar diblock copolymers, polybutadiene-b-poly(acrylic acid), PBd-b-PAA (M_w = 5.8–4 kg mol⁻¹) and poly(styrene)-b-poly(ethylene oxide), PS-b-PEO (M_w = 9–5 kg mol⁻¹) were blended in an effort to achieve morphologies typical of triblock copolymers. Blend compatibility was achieved by the hydrogen bond driven association of the PAA block of one diblock with the PEO block of the other. Small angle X-ray scattering was used to determine the morphologies of the compositions, which were further investigated using transmission electron microscopy and selective staining techniques. The crystallinity of the PEO block was determined by differential scanning calorimetry. The hydrogen bond interactions between PEO and PAA yielded a complex triblock lamellar morphology of the form PS-b-(PEO/PAA)-b-PBd-b-(PEO/PAA). This morphology was stable when crystallization of PEO was suppressed by sufficient interaction with PAA.     

Synthesis and self‐assembly of diblock copolymers bearing 2‐nitrobenzyl photocleavable side groups

The light‐responsive behavior in solution and in thin films of block copolymers bearing 2‐nitrobenzyl photocleavable esters as side groups is discussed in this article. The polymers were synthesized by grafting 2‐nitrobenzyl moieties onto poly(acrylic acid)‐block‐polystyrene (PAA‐b‐PS) precursor polymers, leading to poly(2‐nitrobenzyl acrylate‐random‐acrylic acid)‐block‐polystyrene (P(NBA‐r‐AA)‐b‐PS) block copolymers. The UV irradiation of the block copolymers in a selective solvent for PS led to the formation of micelles that were used to trap hydrophilic molecules inside their core (light‐induced encapsulation). In addition, thin films consisting of light‐responsive P(NBA‐r‐AA) cylinders surrounded by a PS matrix were achieved by the self‐assembly of P(NBA‐r‐AA)‐b‐PS copolymers onto silicon substrates. Exposing these films to UV irradiation generates nanostructured materials containing carboxylic acids inside the cylindrical nanodomains. The availability of these chemical functions was demonstrated by reacting them with a functional fluorescent dye. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

两亲性杂壳聚合物粒子的高效制备及以其作为模板合成金纳米簇合物

将等质量的嵌段聚合物聚乙烯基萘聚丙烯酸和聚氧化乙烯聚丙烯酸（P2VN-b-PAA和PEO-b-PAA）溶解于N,N′-二甲基甲酰胺(DMF)中,加入小分子二元胺（1,2-丙二胺,PDA）,制备出均匀的两亲性杂壳聚合物纳米粒子(MSNPs)。 该粒子以PEO和P2VN混合嵌段为壳层,非共价键交联的PAA嵌段为核,在水相及有机相中均可稳定分散,具有典型的两亲性特点。 扫描电子显微镜和光散射测试结果表明,该杂壳聚合物粒子(MSNPs)的粒径在300 nm左右,分布较均匀,并显示出壳层可塌缩变形的疏松核（软粒子）特征。 以该聚合物粒子(MSNPs)为模板,可以方便制备出金纳米粒子簇合物。     

pH responsive surfaces with nanoscale topography

We report the preparation of nanostructured adaptive polymer surfaces by diffusion of an amphihilic block copolymer toward the interface. The surface segregation of a diblock copolymer, polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA), occurred when blended with high molecular weight polystyrene employed as a matrix. On annealing, the polymer surfaces changed both the chemical composition and the hydrophilicity depending on the environment and pH, respectively. By exposure to either water vapor or air, the surface wettability varied between hydrophilic and hydrophobic. In addition, surface enrichment on diblock copolymer by water vapor annealing led to self‐assembly occurring at the interface. Hence, nanostructured domains can be observed by AFM in liquid media. Moreover, the PAA segments placed at the interface respond to pH and can switch from an extended hydrophilic state at basic pH values to a collapsed hydrophobic state in acidic media. Accordingly, the surface morphology changed from swelled micelles to nanometer size holes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2982–2990, 2010     

Preparation and properties of superabsorbent containing starch and sodium humate

Starch and sodium humate were utilized as raw material for synthesizing starch‐g‐poly(acrylic acid)/sodium humate (St‐g‐PAA/SH) superabsorbent by graft copolymerization reaction of starch (St) and acrylic acid (AA) in the presence of sodium humate (SH) in aqueous solution. The effect of weight ratio of AA to St, initial monomer concentration, neutralization degree of AA, amount of crosslinker, initiator and SH on water absorbency of the superabsorbent were studied. The swelling rate and swelling behavior in NaCl solution as well as reswelling ability of the superabsorbent were systematically investigated. The results showed that the superabsorbent synthesized under optimal conditions with SH content of 7.7 wt% and St content of 11.5 wt% exhibits water absorbency of 1100 g/g in distilled water and 86 g/g in 0.9 wt% NaCl solution, respectively. Introducing SH into the St‐g‐PAA polymeric network can improved the swelling rate and reswelling capability of the superabsorbent. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of a liquid crystalline block on the microdomain structure of block copolymers

We report on the phase behavior and microdomain structure of two types of diblock copolymers containing a liquid crystal (LC) block joined to a flexible coil block. Consideration of the symmetry groups of the liquid crystalline phases and of the block copolymer microdomain structures provides a rationale for predicting the possible types of liquid crystalline block copolymer morphologies. Both previously reported and newly discovered structural types are identified. Possible organizational schemes are developed for the mesogens and periodic disclination defects with respect to the intermaterial dividing surfaces separating the liquid crystalline and flexible coil domains. The first type of copolymer investigated has a rod-like LC block whereas the second type copolymer has a side chain LC block. Five different rod-coil diblocks based on poly(hexyl isocyanate-b-styrene) P(HIC-b-S) were synthesized by anionic polymerization. Wavy lamellae, zig-zag and arrowhead microdomain morphologies corresponding to smectic-C and smectic-O structures were observed depending on the composition. These layered phases have the director (PHIC chain axis) tilted at various orientations with respect to the layer normal. Side-chain LC diblocks based on functionalized poly(isoprene-b-styrene) P(I-b-S) were also investigated. These polymers were synthesized using polymer analogous chemistry from P(I-b-S) precursors. Three different mesogenic groups were attached to the PI blocks: one based on biphenyl benzoate and two based on azobenzene. The microdomain structures found for the functionalized poly(isoprene side-chain LC-b-styrene) P(ILC-b-S) diblocks are typical of traditional coil-coil diblocks (lamellae and cylinders). However, these morphologies possess an additional smectic layering of the mesogens within the microdomains of the LC block. In the case of the rod-coil diblocks, the transformation from an initially isotropic state to the final microphase separated solid state occurs via nematic and then smectic liquid crystalline states, whereas for the side-chain LC-coil cases, the microphase separation transition occurs prior to development of orientational order. The long-range microdomain order of LC block-coil block copolymers can extend over very large distances due to the influence of the orientational ordering of the LC block.     

Self-association dynamics and morphology of short polymeric PBA-b/co-PAA surfactants

The self-association characteristics of very short and well-defined poly(butyl acrylate)-b-poly(acrylic acid) (PBA-b-PAA) block copolymers in water have been studied. The diblocks are asymmetric with the PBA block longer than the PAA block, giving rise to hollow sphere morphology. This is affirmed by experimental data and theoretical evaluations of the hydrophilic and hydrophobic domain sizes, as well as a value close to 1 for the ratio of the hydrodynamic to the gyration radius of the micelles. Besides, the untypically short PBA blocks (polymerization number around 15) render the micelles dynamic. Indications in support include among others the following: the CMC (critical micellar concentration) values depend, together with the aggregation numbers and the micellar sizes, on the block lengths, as predicted by theory; above the CMC their sizes are concentration-independent, while the micelles disappear below CMC. A comparison was also made with a random PBA-co-PAA copolymer of similar length, which self-associates at an apparent CMC 1 order of magnitude larger than those of the block copolymers, but the size of the formed micelles depends on the concentration.     

Self‐assembled complexes of poly(acrylic acid) and poly(styrene)‐block‐poly(4‐vinyl pyridine)

Polymer complexes were prepared from high molecular weight poly(acrylic acid) (PAA) and poly(styrene)‐block‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) in dimethyl formamide (DMF). The hydrogen bonding interactions, phase behavior, and morphology of the complexes were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this A‐b‐B/C type block copolymer/homopolymer system, P4VP block of the block copolymer has strong intermolecular interaction with PAA which led to the formation of nanostructured micelles at various PAA concentrations. The pure PS‐b‐P4VP block copolymer showed a cylindrical rodlike morphology. Spherical micelles were observed in the complexes and the size of the micelles increased with increasing PAA concentration. The micelles are composed of hydrogen‐bonded PAA/P4VP core and non‐bonded PS corona. Finally, a model was proposed to explain the microphase morphology of complex based on the experimental results obtained. The selective swelling of the PS‐b‐P4VP block copolymer by PAA resulted in the formation of different micelles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1192–1202, 2009     

Efficient Synthesis of Poly(acrylic acid) in Aqueous Solution via a RAFT Process

The direct polymerization of acrylic acid (AA) in aqueous solution for high molecular weight by means of living radical polymerization is still difficult. Here, AA was polymerized homogeneously in water by a reversible addition-fragmentation transfer polymerization (RAFT) in the presence of a water-soluble trithiocarbonate as a RAFT agent. Various ratios [AA]:[RAFT agent] were investigated to aim at different molecular weights. The polymerization exhibited living free-radical polymerization characteristics at different ratios [AA]: [RAFT agent]: controlled molecular weight, low polydispersity and well-suited linear growth of the number-average molecular weight, M _n with conversion. The chain transfer to solvent or polymer was suppressed during the polymerization process, thus high linear PAA with high molecular weight and low PDI can be obtained. Moreover, using the generated PAA as a macro RAFT agent, the chain extension polymerization of PAA with fresh AA displayed controlled behavior, demonstrated the ability of PAA to reinitiate sequential polymerization.     

Electrostatic self-assembly of neutral and polyelectrolyte block copolymers and oppositely charged surfactant

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.     

Environmentally responsive particles: from superhydrophobic particle films to water-dispersible microspheres

We describe the preparation, by precipitation copolymerization, of multifunctional divinylbenzene-co-pentafluorostyrene microspheres able to produce superhydrophobic surfaces or disperse in aqueous media upon annealing either in air or water, respectively. For that purpose, an amphiphilic block copolymer, polystyrene-b-poly(acrylic acid), was introduced in the initial feed composed of divinylbenzene and 2,3,4,5,6-pentafluorostyrene. As a result, fluorinated particles were obtained in which the diblock copolymer was encapsulated during the polymerization step. Upon annealing in dry air, the particles are completely hydrophobic and form superhydrophobic surfaces. On the contrary, annealing in water induces the reorientation of the PAA groups toward the particle interface, thus the particles can be dispersed in aqueous media. In addition, the presence of carboxylic acid groups at the particle interface permits us to switch the surface charge between negative and neutral depending on the environmental pH.     

Water-soluble polypyrroles by matrix polymerization: Interpolymer complexes

A new class of water-soluble polypyrroles (PPy) has been developed. This was accomplished by oxidative matrix polymerization of pyrrole (Py) monomer with Ce(IV) in the presence of poly(acrylic acid) (PAA), poly(vinyl pyrrolidone) (PVP), and copolymers (CP) of vinyl pyrrolidone(VP) with acrylic acid (AA) [VP/AA; 25/75 (CP₁), 50/50 (CP₂), 75/25 (CP₃)]. The soluble and insoluble interpolymer complexes were observed according to the nature (and conformation) of polymers in mixture, the ratio of components, and the pH of solutions. The role of PAA, PVP, CP, Py, and Ce(IV) concentrations, the order of component addition, and the pH of the solutions were investigated. The evidence and structural reasons for the formation of soluble interpolymer complexes of PPy with different polymers are discussed. It is proposed that the compactization of the polymer matrix as well as the disturbance of the regularity of reactive groups on the polymer chain decreases the possibility of formation of soluble interpolymer complexes. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1255–1263, 1997