Acrylamido ) -2-methylpropanesulfonate Research Articles

Polyion Complex Vesicles with Solvated Phosphobetaine Shells Formed from Oppositely Charged Diblock Copolymers.

Diblock copolymers consisting of a hydrophilic poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) block and either a cationic or anionic block were prepared from (3-(methacrylamido)propyl)trimethylammonium chloride (MAPTAC) or sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS). Polymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization using a PMPC macro-chain transfer agent. The degree of polymerization for PMPC, cationic PMAPTAC, and anionic PAMPS blocks was 20, 190, and 196, respectively. Combining two solutions of oppositely charged diblock copolymers, PMPC-b-PMAPTAC and PMPC-b-PAMPS, led to the spontaneous formation of polyion complex vesicles (PICsomes). The PICsomes were characterized using 1H NMR, static abd dynamic light scattering, transmittance electron microscopy (TEM), and atomic force microscopy. Maximum hydrodynamic radius (Rh) for the PICsome was observed at a neutral charge balance of the cationic and anionic diblock copolymers. The Rh value and aggregation number (Nagg) of PICsomes in 0.1 M NaCl was 78.0 nm and 7770, respectively. A spherical hollow vesicle structure was observed in TEM images. The hydrodynamic size of the PICsomes increased with concentration of the diblock copolymer solutions before mixing. Thus, the size of the PICsomes can be controlled by selecting an appropriate preparation method.

Formation of Polyion Complex (PIC) Micelles and Vesicles with Anionic pH-Responsive Unimer Micelles and Cationic Diblock Copolymers in Water.

A random copolymer (p(A/MaU)) of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and sodium 11-methacrylamidoundecanate (MaU) was prepared via conventional radical polymerization, which formed a unimer micelle under acidic conditions due to intramolecular hydrophobic interactions between the pendant undecanoic acid groups. Under basic conditions, unimer micelles were opened up to an expanded chain conformation by electrostatic repulsion between the pendant sulfonate and undecanoate anions. A cationic diblock copolymer (P163M99) consisting of poly(3-(methacrylamido)propyl)trimethylammonium chloride (PMAPTAC) and hydrophilic polybetaine, 2-(methacryloyloxy)ethylphosphorylcholine (MPC), blocks was prepared via controlled radical polymerization. Mixing of p(A/MaU) and P163M99 in 0.1 M aqueous NaCl under acidic conditions resulted in the formation of spherical polyion complex (PIC) micelles and vesicles, depending on polymer concentration before mixing. Shapes of the PIC micelles and vesicles changed under basic conditions due to collapse of the charge balance between p(A/MaU) and P163M99. The PIC vesicles can incorporate nonionic hydrophilic guest molecules, and the PIC micelles and vesicles can accept hydrophobic guest molecules in the hydrophobic core formed from p(A/MaU).

Salt and Heat Induced Aggregation of Diblock Copolymers of Sodium 2-(acrylamido)-2-methylpropanesulfonate and N-Isopropylacrylamide in Aqueous Solutions

Heat and salt induced aggregation of three well-defined double hydrophilic block copolymers (DHBCs) of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and N-isopropylacrylamide (NIPAM) with constant chain length of the PAMPS block (with number-average degree of polymerization, DP n = 61) and varying chain length of the PNIPAM block with DP n = 11, 23, and 34 synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization was investigated by turbidity, dynamic light scattering (DLS) and 1H NMR measurements. In the presence of salt or with an increase in temperature, the diblock copolymers form micelles with a PNIPAM core and PAMPS corona. The heat and salt induced aggregation in dilute aqueous solutions dependant on the molecular characteristics of the DHBC (DP n of the PNIPAM block) was observed. The DHBC becomes amphiphilic as the PNIPAM block loses hydrophilicity at higher temperature above its lower critical solution temperature (LCST). Furthermore, the presence of salt induces salting out effect of the uncharged PNIPAM block. The diblock copolymer thus forms nanosized aggregates at a high temperature or in the presence of salt. These aggregates may be multiple aggregates due to inter-micellar aggregation of the spherical core-corona micelles.

Complex Nanoparticles Based on Chitosan and Ionic/Nonionic Strong Polyanions: Formation, Stability, and Application

Interpolyelectrolyte complex (IPEC) nanoparticles formed between chitosan having different molar masses (470, 670, and 780 kDa) and two random copolymers of 2-(acrylamido)-2-methylpropanesulfonate (AMPS) with tert-butylacrylamide (TBA) [P(AMPS(54)-co-TBA(46)) and P(AMPS(37)-co-TBA(63))] were prepared by the dropwise addition of polyanion onto the chitosan solution. The effect of polyelectrolyte characteristics and the molar ratio between charges on the morphology of the complex nanoparticles and on their colloidal stability was deeply investigated by turbidimetric titration (optical density at 500 nm), dynamic light scattering, and atomic force microscopy. It was found that the lowest sizes of the IPEC nanoparticles were obtained, with both polyanions, when the chitosan having the lowest molar mass (470 kDa) was used as a major component. In this case, the particle sizes varied in a narrow range, even after the complex stoichiometry; i.e., when the polyanion was added in excess, the colloidal stability of these IPEC dispersions was very high. A mechanism of complex formation as a function of the ratio between charges was proposed. According to this mechanism, the nonstoichiometric complex nanoparticles formed at molar ratios between charges, n(-)/n+, lower than 0.2, i.e., far from the complex stoichiometry, would have a high density of positive charges in excess not only because of the chitosan in excess, which forms the shell, but also because of the mismatch of opposite charges, due to both the differences in the flexibility of complementary polyions and the presence of the hydrophobic comonomer, TBA, in the polyanion structure. Nonstoichiometric IPECs prepared at n(-)/n+ around 0.2 proved to be more efficient than chitosan in the destabilization of kaolin from a model suspension, with a lower optimum concentration flocculation and a much larger flocculation window being found compared with chitosan.

Micellization Behavior of an Amphiphilic Statistical Copolymer in Water-Methanol Mixtures

Sedimentation equilibrium measurements were made on an amphiphilic statistical copolymer p(AMPS/C6) made of sodium 2-(acrylamido)-2-methylpropane-sulfonate (AMPS) and n-hexyl methacrylate (C6), dissolved in water-methanol mixtures with 0.2M LiClO4 and different methanol contents over a wide polymer concentration range. The experimental results were analyzed in terms of a micellar solution theory for amphiphilic polyelectrolytes to estimate the aggregation number m of the micelle and the internal free energy change Δm/m (per polymer chain) due to micellization. Both m and Δm/mdecreased with increasing the methanol content in the solvent. In addition, dynamic light scattering for the same copolymer system indicated that p(AMPS/C6) formed a uni-core star-like micelle in water-methanol mixture with the methanol mole fractions of 0 and 0.06.

Synthesis of Oppositely Charged Block Copolymers of Poly(ethylene glycol) via Reversible Addition−Fragmentation Chain Transfer Radical Polymerization and Characterization of Their Polyion Complex Micelles in Water

Diblock copolymers consisting of a water-soluble nonionic block and either an anionic or cationic block were prepared from sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) or (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) via reversible addition−fragmentation chain transfer (RAFT)-controlled radical polymerization using poly(ethylene glycol) (PEG)-based chain transfer agent (PEG-CTA) in water. The RAFT polymerization proceeded in a living fashion, as suggested by the observation that the number-average molecular weight (Mn) increased linearly with the monomer conversion (up to conversions of 30% for MAPTAC and 50% for AMPS), whereas the polydispersity (Mw/Mn) remained nearly constant (Mw/Mn < 1.05 for MAPTAC and <1.2 for AMPS) independent of the conversion. The mixing of aqueous solutions of the oppositely charged diblock copolymers, PEG-b-PAMPS and PEG-b-PMAPTAC, led to the spontaneous formation of polyion complex (PIC) micelles. The PIC micelles were characterized by 1H NMR spin−spin relaxation time, static light scattering (SLS), dynamic light scattering (DLS), and scanning electron microscopy (SEM) techniques. The hydrodynamic size of the micelle depended on the mixing ratio of PEG-b-PAMPS and PEG-b-PMAPTAC with the size maximizing at the mixing ratio of stoichiometric charge neutralization. The mixing of the oppositely charged diblock copolymers with shorter charged blocks formed a core−shell PIC micelle. In contrast, a complicated aggregate was formed from a pair of longer blocks. The exact structure of the aggregate is still an open question, but it is speculated to be a multicore intermicellar aggregate on the basis of various characterization data.

Associative Properties in Water of Copolymers of Sodium 2-(Acrylamido)-2-methylpropanesulfonate and Methacrylamides Substituted with Alkyl Groups of Varying Lengths

Associative properties of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) with N-hexylmethacrylamide (C6MAm) and with N-octadecylmethacrylamide (C18MAm) in aqueous solutions were investigated comparing with those of AMPS copolymers with N-dodecylmethacrylamide (C12MAm) reported previously. For characterization by fluorescence, all the polymers were labeled with 1 mol % of naphthalene by terpolymerization using N-(1-naphthylmethyl)methacrylamide. The polymers possessing C6 or C12 alkyl chains exhibit a strong tendency for intramolecular hydrophobic association to form unimolecular micelles when the CnMAm (n = 6, 12) contents in the polymers are in the ranges of 30−70 and 10−50 mol % for the C6 and C12 chains, respectively. A similar tendency was observed for the polymers possessing C18 chains when the C18MAm contents are in the range of 5−20 mol %, but polymer micelles formed were not completely unimolecular. Both the lower and upper limits of the CnMAm contents for all the three polymers decrease significantly with increasing the length of the alkyl chain. When the CnMAm contents are either lower or higher than these limits, the polymer-bound alkyl chains undergo interpolymer associations. Fluorescence depolarization and 1H NMR relaxation times indicate that local motions of naphthalene labels and alkyl chains are more pronouncedly restricted in hydrophobic domains formed by longer alkyl chains. An inclination to the self-association of these polymers was discussed in terms of the ratio of the total number of carbon atoms in hydrophobes to the number of SO3- in a polymer chain. A conclusion is that with C6 chains one needs to incorporate more carbon atoms into a polymer than with C12 and C18 chains to attain the same extent of hydrophobe associations. In other words, the CH2 and CH3 residues in the C6 chain are much less effective than those in the C12 and C18 chains for the self-association when compared at the same hydrophobe/charge ratio in a polymer chain, whereas there is no significant difference between those in the C12 and C18 chains. Thus, the ability of the C6, C12, and C18 chains per carbon atom to associate is in the order C18 ≥ C12 ≫ C6.

Solution Properties of Micelle Networks Formed by Nonionic Surfactant Moieties Covalently Bound to a Polyelectrolyte: Salt Effects on Rheological Behavior

Rheological properties of aqueous solutions of micelle networks formed by a copolymer of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and an associative macromonomer, methacrylate substituted with HO(CH2CH2O)25C12H25 (C12E25) (20 mol % content in the copolymer), were investigated as a function of the polymer concentration (Cp), added salt concentration ([NaCl]), and shear stress. The polymer-bound C12E25 surfactant moieties form micelles via intra- and interpolymer association. These polymer-bound micelles are bridged by polymer chains and hence form a network structure. The solution viscosity of this micelle network increases markedly with increasing Cp near 10 g/L (at [NaCl] = 0.10 M) and beyond this Cp the number of micelle bridges greatly increases with increasing Cp. The extent of the micelle bridging depends on [NaCl]. When Cp is sufficiently high, where interpolymer associations are favorable, steady-state viscosity measured at a low-shear rate increases with increasing [NaCl], exhibiting a maximum value at [NaCl] ≈ 0.13 M (at Cp = 25.0 g/L), and then decreases as [NaCl] is further increased. The micelle network solutions exhibit shear-dependent viscosity behavior, i.e., Newtonian behavior at low shear rates (<30 s-1), shear thickening at intermediate shear rates (30−200 s-1), and shear thinning at higher shear rates (>200 s-1). Furthermore, the solutions behave as a viscoelastic fluid at low polymer concentrations (Cp ≤ 25.0 g/L) but they show significant elastic properties with increasing Cp, both storage and loss moduli increasing greatly with increasing Cp and the two moduli becoming close to each other. When Cp is increased to ca. 100 g/L or higher, the micelle network system exhibits gel-like behavior with a plateau modulus (G0) increasing markedly with increasing Cp whereas a terminal relaxation time (λ) remaining practically the same (ca. 10 ms). The value of G0 increases with increasing [NaCl], passing through a maximum at [NaCl] ≈ 0.13 M (at Cp = 25 g/L), and then decreases with further increasing [NaCl]. Thus, the viscosity is virtually governed by G0 but not by λ. The micelle bridge is dynamic in nature, which makes the disruption and re-formation of the micelle bridge occur reversibly in response to external stimuli.

Micelle Formation of Random Copolymers of Sodium 2-(Acrylamido)-2-methylpropanesulfonate and a Nonionic Surfactant Macromonomer in Water As Studied by Fluorescence and Dynamic Light Scattering

A polyelectrolyte-bound nonionic surfactant (HO(CH2CH2O)25C12H25) (C12E25) system was prepared by copolymerization of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and a methacrylate substituted with HO(CH2CH2O)25C12H25 in N,N-dimethylformamide initiated by 2,2‘-azobis(isobutyronitrile). The contents of the surfactant macromonomer unit (fDE25) in the copolymers are in the range 10−30 mol %. Dry samples of these copolymers are soluble in water, polymer-bound surfactants undergoing micellization. The micelle formation was studied by fluorescence and quasielastic light scattering (QELS) techniques in 0.1 M NaCl aqueous solutions. Steady-state fluorescence data for pyrene probes solubilized in water in the presence of the copolymers suggest that the polymer-bound surfactants associate in both intra- and interpolymer fashions to form micelles. The interpolymer hydrophobic associations were found to commence to occur at a relatively well-defined polymer concentration (Cp), which can be regarded as an apparent “cmc” for interpolymer micelle formation. Such cmc values are 10−100 times smaller than that for discrete C12E25 molecules, the values increasing with increasing fDE25. Mean aggregation numbers (Nagg) of the terminal dodecyl groups at an end of the (CH2CH2O)25 spacer group were estimated by a time-dependent fluorescence method. Nagg values were found to be of the same order of that for the discrete C12E25 micelles although the values for the polymer-bound surfactant micelles are somewhat larger than that for the free micelle. The Nagg values were relatively constant over a significant range of Cp. QELS data indicated bimodal distributions of relaxation times with a fast and a slow relaxation mode. The slow mode component is due to polymer aggregates that include a number of micelle units formed by polymer-bound C12E25 groups. On the other hand, the fast mode component may be attributed to either a “unimeric” micelle (a micelle formed by a single polymer chain) or an “oligomeric” micelle (a micelle formed by a small number of polymer chains). Hydrodynamic radii (Rh) for the slow mode component are on the order of 60−170 nm exhibiting a tendency to increase with increasing Cp whereas those for the fast mode are 6−8 nm independent of Cp. Rh for discrete C12E25 micelle was found to be ca. 5 nm under the same conditions. On the basis of the characterization, a hypothetical micelle model was proposed where micelle units formed from polymer-bound C12E25 moieties are bridged by polymer chains yielding a micelle network structure.

Determination of the compositional distribution of copolymers by frontal analysis continuous capillary electrophoresis.

Frontal analysis continuous capillary electrophoresis (FACCE) was carried out for a series of random copolymers of an ionic monomer, sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS), and a nonionic monomer, acrylamide (AAM). The electropherograms appeared in order of anionic content and were generally sigmoidal, in contrast to that of hyaluronic acid (HA), which was abrupt and discontinuous. This difference could be related to the compositional heterogeneity of the copolymers, completely absent in the biopolymer. Through the range of copolymer composition (10-100% AMPS) the relationship between average mobility and nominal AMPS content could be described by a calibration curve, making it possible to deduce the compositional distribution of copolymer samples.

Self-Association of Dodecyl Moieties Covalently Linked to a Polyelectrolyte in a Small Amount

Self-association behavior of random copolymers of sodium 2-(acrylamido)-2-methylpropane sulfonate (AMPS) and N-dodecylmethacrylamide (DodMAm) with low DOdMAm contents (fDod) of 2.5−10 mol% was investigated mainly by QELS. In the case of the copolymer with fDod=10 mol%, the relaxation time distribution is unimodal independent of the polymer concentration. On the other hand, in the case of the copolymers with fDod=2.5−7.5 mol%, the relaxation time distributions became bimodal at polymer concentrations >5 g/L, indicating interpolymer associations occurring at higher concentrations of the polymers. From QELS results, apparent values of hydrodynamic radii (Rh) for unimers and the interpolymer associates were estimated to be ca. 6−7 and ca. 120 nm, respectively. The interpolymer associates were found to be disrupted by the addition of a nonionic surfactant, n-dodecyl hexaethylene glycol monoether.

Effect of Hydrophobe Content on Intra- and Interpolymer Self-Associations of Hydrophobically Modified Poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) in Water

As an extension of our previous fluorescence studies of random terpolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS), N-dodecylmethacrylamide (DodMAm), and 1 mol % N-(1-naphthylmethyl)methacrylamide (fluorescence label), intra- and interpolymer self-associations of these polymers in aqueous solution were investigated by 1H NMR relaxation, fluorescence depolarization, and quasielastic light scattering (QELS) methods. These studies were conducted with a focus on the effect of the DodMAm content (fDod) on the association behavior of these polymers over the fDod range of 10−60 mol %. At fDod = 10 mol %, the polymer-bound dodecyl groups undergo mostly intrapolymer association, but a small fraction of the hydrophobes undergo interpolymer association, QELS showing a bimodal distribution as the polymer concentration is increased. In the range 10 < fDod ≤ 50 mol %, however, QELS data indicated a strong preference for intrapolymer associations independent of the polymer concentration, leading to the ...

Interpolymer Association of Cholesterol Pendants Linked to a Polyelectrolyte As Studied by Quasielastic Light Scattering and Fluorescence Techniques

The association behavior of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and cholesteryl 6-methacryloyloxyhexanoate (Chol-C5-MA) in 0.1 M NaCl aqueous solutions was investigated by quasielastic light scattering and fluorescence techniques to gain further insights into the structures and properties of their “intermolecularly bridged flower-type micelles” which we had proposed previously. When the Chol-C5-MA content in the copolymer was as low as 1 mol %, unimers were found to coexist with the interpolymer aggregates independent of the polymer concentration (CP) in a range 0.1 < CP < 10 g/L. However, when the Chol-C5-MA content was increased to 5 mol %, virtually all the polymer chains form multipolymer aggregates which can be viewed as an assembly of flower-type micelles where polymer chains are “cross-linked” via Chol associations. The aggregation number of Chol moieties was estimated to be 17−19 for the copolymer of 5 mol % Chol-C5-MA by a time-resolved fluorescence quenchin...

Interactions of Amphiphilic Polyelectrolytes and Neutral Polymeric Micelles: A Study by Nonradiative Energy Transfer

The interactions of hydrophobically modified poly(N-isopropylacrylamides) (HM-PNIPAM) and unimolecular micelles formed by fluorescently labeled copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and N-n-dodecylmethacrylamide or N-adamantylmethacrylamide were investigated by fluorescence spectroscopy and dynamic light scattering measurements. The HM-PNIPAM copolymers were prepared by free-radical copolymerization of N-isopropylacrylamide (NIPAM) and either N-n-dodecylacrylamide or N-(1-adamantylacrylamide). Pyrene- and naphthalene-labeled HM-PNIPAM derivatives were prepared by reaction of 1-pyrenylmethylamine, 4-(1-pyrenyl)butylamine, or 1-(1-naphthyl)ethylamine with copolymers of NIPAM, the hydrophobic monomer, and N-(acryloxysuccinimide). In aqueous solutions, the HM-PNIPAM copolymers form multimolecular micelles ranging in size from 25 to 60 nm (25 °C), as determined by dynamic light scattering and fluorescence measurements based on the extent of nonradiative energy transfer (NRET) between naphthalene and pyrene in mixtures of naphthalene- and pyrene-labeled HM-PNIPAM derivatives. The interactions between HM-PNIPAM and hydrophobically modified PAMPS were studied by NRET measurements in solutions of (1) naphthalene-labeled HM-PNIPAM and pyrene-labeled PAMPS and (2) unlabeled HM-PNIPAM and a copolymer of AMPS carrying both naphthalene and pyrene chromophores. Each technique gave evidence for the formation of complexes between PAMPS micelles and HM-PNIPAM chains. The complexation was shown to depend on temperature, the ratio of the two polymers, and the molecular structure of the hydrophobic substituents.

Hydrophobic Association of Random Copolymers of Sodium 2-(Acrylamido)-2-methylpropanesulfonate and Dodecyl Methacrylate in Water As Studied by Fluorescence and Dynamic Light Scattering

The association behavior of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and dodecyl methacrylate (DMA) with its content (fDMA) varying from 1 to 15 mol % was investigated by fluorescence and quasielastic light scattering (QELS) techniques in 0.1 M NaCl aqueous solutions. The association behavior of the copolymers was found to depend strongly on fDMA. When fDMA < 3 mol %, some polymer chains exist as unimers with a hydrodynamic radius (Rh) of about 5 nm while some polymers form multipolymer aggregates with Rh ≈ 100 nm, arising from “hydrophobic cross-linking” by the interpolymer association of dodecyl groups. When fDMA is increased to 9 mol %, interpolymer hydrophobe associations lead to the formation of a multipolymer micelle with Rh ≈ 10−13 nm. The aggregation number (Nagg) of dodecyl groups in a micelle core was estimated to be about 195. When fDMA is further increased to 15 mol %, Rh for the multipolymer micelle markedly increases to 70−180 nm, the size increasing with in...

Fluorescence Studies of Hydrophobic Association of Random Copolymers of Sodium 2-(Acrylamido)-2-methylpropanesulfonate and N-Dodecylmethacrylamide in Water

Intrapolymer self-association of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and N-dodecylmethacrylamide (DodMAm) with varying compositions in aqueous solution was investigated by various fluorescence techniques. The polymers were labeled with 1 mol % of naphthalene (Np) or pyrene (Py) or doubly labeled with Np (4 mol %) and Py (1 mol %). Vibronic fine structures of Py fluorescence, lifetimes of Np and Py fluorescence, intrapolymer nonradiative energy transfer (NRET) from singlet excited Np to ground-state Py labels, and fluorescence quenching by thallium cations were investigated as a function of the DodMAm content (fDod) in the copolymers with or without added salt. Results from all these fluorescence studies indicate that with increasing fDod, hydrophobic association commences at fDod ≅ 20 mol % in pure water and at fDod ≅ 10 mol % in 0.1 M NaCl, showing a saturation tendency near fDod ≅ 40 mol % in the salt solution. In contrast, viscosity data show that the polymer size...