Block Polyampholytes Research Articles

Macromolecular complexes of polyampholytes

Abstract The macromolecular complexes of random, regular, graft, block and dendritic polyampholytes with respect to transition metal ions, surfactants, dyes, polyelectrolytes, and proteins are discussed in this review. Application aspects of macromolecular complexes of polyampholytes in biotechnology, medicine, nanotechnology, catalysis are demonstrated.

Charge regulation mechanism in end-tethered weak polyampholytes.

Weak polyampholytes, containing oppositely charged dissociable groups, are expected to be responsive to changes in ionic conditions. Here, we determine structural and thermodynamic properties, including the charged groups' degrees of dissociation, of end-tethered weak polyampholyte layers as a function of salt concentration, pH, and the solvent quality. For diblock weak polyampholytes grafted by their acidic blocks, we find that the acidic monomers increase their charge while the basic monomers decrease their charge with decreasing salt concentration for pH values less than the pKa value of both monomers and vice versa when the pH > pKa. This complex charge regulation occurs because the electrostatic attraction between oppositely charged blocks is stronger than the repulsion between monomers with the same charge in both good and poor solvents when the screening by salt ions is weak. This is evidenced by the retraction of the top block into the bottom layer. In the case of poor solvent conditions to the basic block (the top block), we find lateral segregation of basic monomers into micelles, forming a two-dimensional hexagonal pattern on the surface at intermediate and high pH values for monovalent salt concentrations from 0.01 to 0.1 M. When the solvent is poor to both blocks, we find lateral segregation of the grafted acidic block into lamellae with longitudinal undulations of low and high acidic monomer density. By exploiting weak block polyampholytes, our work expands the parameter space for creating responsive surfaces stable over a wide range of pH and salt concentration.

Small ion effects on self-coacervation phenomena in block polyampholytes.

Self-coacervation is a phenomenon in which a solution of polyampholytes spontaneously phase separates into a dense liquid coacervate phase, rich in the polyampholyte, coexisting with a dilute supernatant phase. Such coacervation results in the formation of membraneless organelles in vivo and has further been applied industrially as synthetic encapsulants and coatings. It has been suggested that coacervation is primarily driven by the entropy gain from releasing counter-ions upon complexation. Using fully fluctuating field-theoretic simulations employing complex Langevin sampling and complementary molecular dynamics simulations, we have determined that the small ions contribute only weakly to the self-coacervation behavior of charge-symmetric block polyampholytes in solution. Salt partitioning between the supernatant and coacervate is also found to be negligible in the weak-binding regime at low electrostatic strengths. Asymmetries in charge distribution along the polyampholytes can cause net-charges that lead to "tadpole" configurations in dilute solution and the suppression of phase separation at low salt content. The field and particle-based simulation results are compared with analytical predictions from the random phase approximation (RPA) and postulated scaling relationships. The qualitative trends are mostly captured by the RPA, but the approximation fails at low concentration.

Molecular design of self-coacervation phenomena in block polyampholytes

Coacervation is a common phenomenon in natural polymers and has been applied to synthetic materials systems for coatings, adhesives, and encapsulants. Single-component coacervates are formed when block polyampholytes exhibit self-coacervation, phase separating into a dense liquid coacervate phase rich in the polyampholyte coexisting with a dilute supernatant phase, a process implicated in the liquid-liquid phase separation of intrinsically disordered proteins. Using fully fluctuating field-theoretic simulations using complex Langevin sampling and complementary molecular-dynamics simulations, we develop molecular design principles to connect the sequenced charge pattern of a polyampholyte with its self-coacervation behavior in solution. In particular, the lengthscale of charged blocks and number of connections between oppositely charged blocks are shown to have a dramatic effect on the tendency to phase separate and on the accessible chain conformations. The field and particle-based simulation results are compared with analytical predictions from the random phase approximation (RPA) and postulated scaling relationships. The qualitative trends are mostly captured by the RPA, but the approximation fails catastrophically at low concentration.

Synthesis of Diblock Polyampholyte PAMPS-b-PMAPTAC and Its Adsorption on Bentonite.

To study the adsorption of polyampholyte on bentonite (Bent), a block polyampholyte, PAMPS-b-PMAPTAC, comprised of 2-Acrylamido-2-Methylpropane Sulfonic Acid (AMPS) units and Methacrylamido Propyl Trimethyl Ammonium Chloride (MAPTAC) units, was synthesized using reversible addition-fragmentation chain transfer polymerization (RAFT) method. The block polyampholyte samples were characterized by FTIR, 1H NMR and Gel Permeation Chromatography (GPC). The microstructure of block polyampholyte and random polyampholyte in deionized water indicated that uneven distribution of charged groups increased the entanglement of polymer chains. Addition of salt weakened the electrostatic interactions among charged groups, and, therefore, increased the zeta potential of polyampholyte in aqueous solutions. The adsorptive behaviors of PAMPS-b-PMAPTAC on Bent were studied using elemental analysis, and the effects of external factors were considered. The adsorption equilibrium of polymers on Bent was reached after 12 h. Increased temperature and increased salinity exerted a positive and negative effect on the adsorption of polyampholyte, respectively. The molecular weight played as the decisive factor for the adsorption of polyampholyte in the absence of NaCl, while the content of cationic groups acted as the main factor in the presence of NaCl. Block polyampholyte exhibited higher adsorption than random polyampholyte in the absence of salt. XRD results also indicated that block polyampholyte had a better intercalation effect than random polyampholyte.

Tunable Compartmentalized Morphologies of Multilayered Dual Responsive Star Block Polyampholytes

Heteroarm star-graft block quarterpolymers [PSn(P2VP-b-PAA-g-PNIPAM)n] with pH-sensitive weak polycationic/polyanionic arms and grafted thermoresponsive outer chains are integrated into hydrogen-bonded multilayers with morphologies distinct from those in traditional layer-by-layer assemblies. We discovered that block-specific swelling promotes heterogeneous partitioning of hydrophobic and hydrophilic reservoirs within the interior of the swollen multilayers. The molecular architecture and amphiphilicity balance governs the internal structure and is regulated via solution pH and temperature. In acidic/basic regimes, competing interactions between hydrophobic and ionized blocks favor compartmentalization of water to the hydrophilic pockets near the substrate surface. Heating the assemblies of star block quarterpolymers with high grafting densities above the lower critical solution temperature of the PNIPAM peripheries promotes the aggregation of the functional “soft nanoparticles” into star-like clusters wh...

“Schizophrenic” Micellization of Poly(Acrylic Acid)-B-Poly(2-Dimethylamino)Ethyl Methacrylate and Responsive Behavior of the Micelles

The well-defined block polyampholyte poly(acrylic acid)-b-poly(2-dimethylamino)ethyl methacrylate (PAA-b-PDMAEMA) was synthesized by sequential atom transfer radical polymerization (ATRP) using protected group chemisty. The block polyampholyte exhibited so-called “schizophrenic” micellization behavior at different pH values. The PAA-core micelles, PDMAEMA-core micelles, and a kind of polyeletrolyte complex were formed in acidic pH (pH < 4.5), basic pH (pH > 9.0), and neutral pH region (5.5–8.5), respectively. The temperature responsive behaviors of the micelles and the complex formed in neutral environment were studied in detail via dynamic light scattering (DLS) and UV-vis transmittance. Salt effect on the temperature responsive behavior was also discussed.[Supplementary materials are available for this article. Go to the publisher's online edition of Soft Materials or http://pubs.acs.org for the following free supplemental resource(s): Synthesis of PtBA-b-PDMAEMA, 1H NMR spectra of block copolymer and TEM image of block copolymer at aqueous solution with NaCl]”

Poly[(sodium sulfamate/carboxylate)isoprene‐b‐2‐vinyl pyridine] block polyampholytes: Synthesis and self‐assembly in aqueous media

AbstractWe report on the synthesis of poly[(sodium sulfamate/carboxylate) isoprene‐b‐2‐vinyl pyridine] block polyampholytes (SCPI‐P2VP), utilizing anionic polymerization and post polymerization functionalization reactions. The precursor poly(isoprene‐b‐(2‐vinylpyridine)) diblock copolymers (PI‐P2VP), containing a polyisoprene (PI) block with high 1,4 microstructure, were prepared by anionic polymerization high vacuum techniques, in two steps, involving change of the polymerization solvent. Subsequent functionalization of the PI block with chlorosulfonyl isocyanate, introduced sulfamate and carboxylate groups in the polymer chains and produced the desired block polyampholytes. The successful synthesis of the polyampolytes was corroborated by elemental analysis and IR spectroscopy measurements. The self‐assembly behaviour of the aforementioned polyampholytes was studied in aqueous solutions as a function of pH, by aid of dynamic and static light scattering, zeta potential, fluorescence spectroscopy and atomic force microscopy. Experimental results indicate that the block polyampholytes form micellar structures with P2VP cores and SCPI coronas at pH &gt; 6, whereas more compact nanoparticles are formed at pH &lt; 4 from the complexation of positively charged P2VP and SCPI, stabilized by excess negative charges of uncomplexed SCI segments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Rheological properties of ABA telechelic polyelectrolyte and ABA polyampholyte reversible hydrogels: A comparative study

Two types of reversible hydrogels formed by poly(t-butyl acrylate)–poly(2-vinyl pyridine)–poly(t-butyl acrylate) (PtBA–P2VP–PtBA) and poly(acrylic acid)–poly(2-vinyl pyridine)–poly(acrylic acid) (PAA–P2VP–PAA), named telechelic polyelectrolyte and block polyampholyte, respectively, of the same degree of polymerization were studied in aqueous solutions at pH 3.7 in terms of their rheological properties. The different structural characteristics of the formed 3D networks that arise from hydrophobic interactions of the telechelic polyelectrolyte and electrostatic interactions of the polyampholyte, lead to significant different rheological properties. The results tend to show that a thermo-sensitive weak hydrogel is formed by the polyampholyte while a stiff, but fragile, hydrogel is formed by the telechelic polyelectrolyte.

RAFT polymerization of styrenic‐based phosphonium monomers and a new family of well‐defined statistical and block polyampholytes

AbstractWe describe herein the first example of the controlled reversible addition‐fragmentation chain transfer (RAFT) radical homo‐ and copolymerization of phosphonium‐based styrenic monomers mediated with a trithiocarbonate‐based RAFT chain transfer agent (CTA) directly in aqueous media. In the case of homopolymer syntheses the polymerizations proceed in a controlled fashion yielding materials with predetermined molecular characteristics as evidenced from the narrow molecular mass distributions (MMD) and the excellent agreement between the theoretical and experimentally determined molecular masses (MM). We also demonstrate the controlled nature of the homopolymerization of 4‐vinylbenzoic acid with the same CTA in DMSO. We subsequently prepared both statistical and block copolymers from the phosphonium/4‐vinylbenzoic acid monomers to yield the first examples of polyampholytes in which the cationic functional group is a quaternary phosphonium species. We show that the kinetic characteristics of the statistical copolymerizations are different from the homopolymerizations and proceed, generally, at a significantly faster rate although there appears to be a composition dependence on the rate. Given the inherent problems in characterizing such polyampholytic copolymers via aqueous size exclusion chromatography we have qualitatively proved their successful formation via FTIR spectroscopy. Finally, in a preliminary experiment we qualitatively demonstrate the ability of such pH‐responsive block copolymers to undergo supramolecular self‐assembly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2468–2483, 2007

Scaling Theory of Diblock Polyampholyte Solutions

We have developed a scaling theory for a salt-free solution of diblock polyampholytes. A charge-symmetric diblock polyampholyte chain with equally charged positive and negative blocks collapses into a globule. This collapse is driven by the electrostatic attraction between oppositely charged blocks. We predict that a charge-asymmetric block polyampholyte has a tadpole shape with a globular head and a polyelectrolyte tail. These tadpoles aggregate into micelles if the electrostatic repulsion between their tails is weaker than the surface energy gain due to aggregation of their heads. First tadpoles form double-tailed micelles. In double-tailed micelles with an aggregation number larger than two, additional chains are completely confined into the core, and the length of the two tails increases proportionally to the total charge of the micelle. If this total charge becomes higher than the charge of two corona blocks of double-tailed micelles, more blocks appear in the corona. Chains are disproportionated in ...

Association Phenomena of Poly(acrylic acid)-b-poly(2-vinylpyridine)- b-poly(acrylic acid) Triblock Polyampholyte in Aqueous Solutions: From Transient Network to Compact Micelles

An asymmetric model triblock copolymer of poly(acrylic acid)-b-poly(vinylpyridine)-b-poly(acrylic acid) (PAA-b-P2VP-b-PAA) was synthesized through anionic polymerization and explored in aqueous media. This block polyampholyte exhibits a rich phase behavior responding to pH changes. At low pH and low concentrations the polymer is molecularly dissolved. At pH close to 3.4 and above a critical concentration, a three-dimensional transient network is formed. The physical cross-links arise from electrostatic interactions among protonated positively charged P2VP units and negatively charged PAA units. In the intermediate pH region (4 < pH < 7) and around the isoelectric point, the polyampholyte is precipitated. The polymer is redissolved at higher pH, forming compact micelles with P2VP hydrophobic cores and extended PAA chains in the corona. The phase behavior of the system is reversible.

Synthesis and aqueous solution characterization of novel diblock polyampholytes containing imidazole

A series of diblock copolymers of 2-(1-imidazolyl)ethyl methacrylate and tetrahydropyranyl methacrylate (THPMA) were synthesized by group transfer polymerization using propylene carbonate rather than tetrahydrofuran as the solvent to ensure homogeneous polymerizations. The resulting copolymers were characterized by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy ( 1H NMR) to determine their molecular weights and compositions, respectively. The THPMA units of the copolymers were subsequently converted to methacrylic acid units by acid hydrolysis. The resulting polyampholytes were characterized in terms of their composition and solubility characteristics using 1H NMR and hydrogen ion titration. Moreover, dynamic light scattering in alkaline water (pH 9.3) indicated the presence of large non-micellar aggregates of the block polyampholytes.

Adsorption of block polyampholyte micelles in monolayers at the silicon water interface

The adsorption of the diblock polyampholyte poly (methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate) from aqueous solution on silicon substrates was investigated as a function of polymer concentration and pH. Dynamic light scattering and electrokinetic measurements were used to characterize the polyampholyte in solution. The amount of polymer adsorbed was determined by ellipsometry and lateral structures of the polymer layer were investigated by scanning force microscopy. The amount of polymer adsorbed was found to be strongly influenced by the pH of the polymer solution, while the size of the polyampholyte micelles adsorbed on the surface was hardly affected by pH during adsorption. From investigations by scanning force microscopy well-seperated micelles were seen in the dried monolayers adsorbed directly from solution. The structures at the surface are correlated to structures in solution, and the adsorbed amount depends on the relative charge of the micelles and the surface.

Effect of Block Size and Sequence on the Micellization of ABC Triblock Methacrylic Polyampholytes

Fluorescence spectroscopy and static and dynamic light scattering were employed to probe the effect of block size and sequence on the micellization properties of a series of water-soluble, low-polydispersity, low-molecular-weight, block and random methacrylic polyampholytes : B 8 M 12 A 16 , B 12 M 12 A 12 , B 16 M 12 A 8 , B 12 A 12 M 12 , and (B-co-M-co-A) 12 , where B is 2-(dimethylamino)ethyl methacrylate (DMAEMA), M is methyl methacrylate (MMA), and A is methacrylic acid (MAA). The values of the pyrene fluorescence emission intensity ratio I i /I 3 , indicative of micelle formation, are reported for both acidic and basic solution pH values, over a wide range of copolymer concentrations (0.0001-0.5% w/w) and at three different temperatures (10, 25, and 50 °C). The critical micellization concentration (CMC) values ordered as CMC-(B 16 M 12 A 8 ) > CMC(B 12 M 12 A 12 ) > CMC(B 8 M 12 A 16 ) at low solution pH. Under basic conditions, the CMC for B 16 M 12 A 8 was slightly lower than that for B 12 M 12 A 12 . Micelles were not formed by the random copolymer (B-co-M-co-A) 12 at either pH value, nor by the triblock B 12 A 12 M 12 at basic pH. A small increase in the CMC with increasing temperature was observed for the BMA copolymers at basic pH. Dynamic light scattering data indicated that, for the micelles formed by the BMA polyampholytes, both DMAEMA and MAA blocks were in the corona regardless of which block was charged, while the middle hydrophobic MMA block constituted the micellar core. The constraints imposed by such a conformation of the polyampholyte blocks resulted in relatively low micelle aggregation numbers of 10-20 and a micelle size about half the contour length of the polymer. The B 12 A 12 M 12 copolymers formed larger micelles than the BMA polyampholytes ; with the MMA block in the center, the micelle radius is determined by the length of the fully-stretched polymer.

Phase behavior of random and ABC triblock methacrylic polyampholytes with poly(vinyl alcohol) in water: effect of pH and salt

ABC triblock and random methacrylic polyampholytes of molecular weight 4,000 g mol −1 with various base-neutral-acid compositions were examined for their phase separation behavior, each in an aqueous mixture with poly(vinyl alcohol) of molecular weight 10,000 g mol −1. Potassium chloride concentration and solution pH were varied and the phase behavior was mapped on the pH-(KCl) space. The block copolymers presented a much broader phase separation region than the random copolymers. This difference may reflect the effect of the structure of the block copolymers which leads to the formation of micelles in solution. The two-phase region of the block copolymers extended over the whole range of potassium chloride concentrations employed in this study, from 0.0 to 0.75 M, and covered the pH range from two pH units below the polyampholyte isoelectric point up to two units above, with the exception of the points at alkaline pH without added salt. The two-phase region of the random copolymers extended from 0.0 to 0.1 M KCl and covered at most one unit in pH, centered near the isoelectric point. The two-phase region of the block copolymers comprised two regimes: the low salt concentration regime characterized by a compact polyampholyte precipitate in equilibrium with a low-viscosity poly(vinyl alcohol) phase; the high salt concentration and alkaline pH regime characterized by two coexisting low-viscosity phases. The one-phase region of the block copolymers extended in the acidic pH range and covered the whole salt concentration range. The ion type effect on the phase behavior of block polyampholytes was related to the position of the ion in the Hofmeister series: high concentrations of salt of low salting out ability resulted in a transition from a two- to a one-phase system.

Turbidimetric Titration Study of the Interaction of Proteins with Acrylic Polyampholytes

AbstractA study of the interaction of proteins [soybean trypsin inhibitor (0.3–1 mg/mL)] with dilute solutions of synthetic polyampholytes (0.05–0.4 mg/mL) composed of acrylic (or methacrylic) acid, (dimethylamino)ethyl methacrylate, and methyl methacrylate was undertaken experimentally using turbidimetric titration. The polyampholytes had a number‐average molecular weight of 4000 (block polyampholytes) or 70000 (random polyampholytes) and a polydispersity index of only 1.3. Alone, the polyampholytes showed a tendency to self‐aggregate around their isoelectric point. Therefore, polyampholyte‐polyampholyte interactions (self‐aggregation) and polyampholyte‐protein complexation behavior were studied as a function of pH (3–9), ionic strength (0–0.75 M) and polymer dosage (50–400 mg of polymer/g of protein). Large increases in turbidity (&gt;500%) were observed for protein‐polyampholyte mixtures (compared to polyampholyte alone) in the case of both block and random copolymers. The observed turbidity increases could be due to protein‐polymer interactions or to enhanced precipitation of polymer in the presence of protein. To differentiate between these alternatives, turbidimetry experiments were carried out at different dosages by (a) keeping the protein concentration constant and varying the polymer concentration and (b) keeping the polymer concentration constant and varying the protein concentration in small steps; they demonstrated that the turbidity increases were indeed due to protein‐polymer interactions. These experiments offer a general methodology to distinguish between intermolecular protein‐polymer and intermolecular polymer‐polymer interactions.