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The use of synthetic hydrogels in wastewater treatment represents a promising and scalable approach to achieving clean water. By modulation of their chemical structure, hydrogels can effectively remove a wide range of toxic compounds, including emerging organic pollutants and heavy metals. For the latter, recovery is essential for both environmental protection and metal recycling. The increasing demand for gold, a nonrenewable metal widely used in many technologies, calls for methods for its selective recovery from complex metal cation solutions. This study explores easy-to-make poly(acrylamide- co -acrylic acid) hydrogels as adsorbents for gold recovery from industrial wastewater containing other precious metals. Such material can reduce gold cations into elemental nanoparticles and microparticles in acid environments at room temperature. This process offers a potential route for metal recovery that is not based on weak interaction or complex formation. Batch tests demonstrate a good adsorption capacity (up to 124 mg/g) and efficient separation from other precious metal ions (Ru, Ir, Pd, Pt, and Rh) in a solution that closely mimics realistic industrial waste conditions. These hydrogels would enable gold recovery also from other complex metal solutions, including those derived from the dissolution of electronic wastes.

Oral delivery of insulin has the potential to revolutionize diabetes care since it is regarded as a noninvasive therapeutic approach without the side effects caused by frequent subcutaneous injection. However, the insulin delivery efficiency through oral route was still limited, likely due to the chemical, enzymatic and absorption barriers. In this study, a novel type of pH- and amylase-responsive microgels as an insulin drug carrier for oral administration was developed to improve the drug delivery efficiency. The microgels were prepared via aqueous dispersion copolymerization of acrylate-grafted-carboxymethyl starch (CMS-g-AA) and 2-isobutyl-acrylic acid (iBAA). The resulting hybrid microgels with the PiBAA contents of 13.6–45.3 wt% exhibited sharp pH-sensitivity, which was revealed by the changes in particle size of the microgels and the transmittance of the microgel aqueous solution. The accelerated decomposition of the CMS-containing microgels in response to amylase was demonstrated by chromogenic reaction and morphology change. Insulin was loaded into the microgels by swelling-diffusion method, and the insulin release from the insulin-loaded microgels in vitro was found to be triggered by pH change and addition of amylase, which was highly dependent on the microgel component. Cytotoxicity assay was performed to show the good biocompatibility of the microgels. In addition, the tests of cellular uptake by Caco-2 cells and transmembrane transport through the Caco-2 cell monolayers were carried out to confirm the intestinal absorption ability of the insulin-loaded microgels. Finally, the oral administration of insulin-loaded microgels to STZ-induced diabetic rats led to a continuous decline in the fasting blood glucose level within 2 to 4 h, and the hypoglycemic effect maintained over 6 h in vivo. The relative pharmacological availability of the insulin-loaded microgels was enhanced 23–38 times compared to free-form insulin solution through oral route. Therefore, the novel starch-based microgels may have potential as an efficient platform for oral insulin delivery. [ABSTRACT FROM AUTHOR]

Controlling the surface properties of solid polymers is important for practical applications. We here succeeded in controlling the surface segregation of polymers to display carboxy groups on an outermost surface, which allowed the covalent immobilization of functional molecules via the carboxy groups on a substrate surface. Random methacrylate-based copolymers containing carboxy groups, which were protected with perfluoroacyl (Rf) groups, were dip-coated on acrylic substrate surfaces. X-ray photoelectron spectroscopy and contact-angle measurements revealed that the Rf groups were segregated to the outermost surface of the dip-coated substrates. The Rf groups were removed by hydrolysis of the Rf esters in the copolymers, resulting in the display of carboxy groups on the surface. The quantification of carboxy groups on a surface revealed that the carboxy groups were reactive to a water-soluble solute in an aqueous solution. The surface segregation was affected by the molecular structure of the copolymer used for dip-coating. [ABSTRACT FROM AUTHOR]

A novel iterative protocol for the synthesis of polydeoxypropionates was developed based on iridium-catalyzed asymmetric hydrogenation of α-substituted acrylic acids. The catalyst loading can be as low as 0.01 mol %, and the overall yield for one iterative cycle is >76%. The reaction conditions are mild, and no organometallic reagents or chromatography steps are required. Using this protocol, (+)-phthioceranic acid and the polydeoxypropionate motifs of ionomycin and borrelidin were synthesized in high yield. [ABSTRACT FROM AUTHOR]

Adhesive hydrogels were prepared by copolymerizing dopamine methacrylamide with either acrylic acid (AAc) or N-(3-aminopropyl)methacrylamide hydrochloride (APMH). The effect of incorporating the anionic and cationic side chains on the oxidation state of catechol was characterized using the FOX assay to track the production of hydrogen peroxide byproduct generated during the autoxidation of catechol, and the interfacial binding property of the adhesive was determined by performing Johnson-Kendall-Roberts contact mechanics tests tested over a wide range of pH values (pH 3.0-9.0). The ionic species contributed to interfacial binding to surfaces with the opposite charge with measured work of adhesion values that were comparable to or in some cases higher than those of catechol. Addition of AAc minimized the oxidation of catechol even at a pH of 8.5 and correspondingly preserved the elevated adhesive property of catechol to both quartz and amine-functionalized surfaces. However, AAc lost its buffering capacity at pH 9.0, and catechol was oxidized at this pH. On the other hand, catechol formed a cohesive covalent bond with the network-bound amine side chain of APMH at basic pH, which interfered with the interfacial binding capability of APMH and the catechol. [ABSTRACT FROM AUTHOR]

Recently, although several unconventional luminescent polymers have been synthesized, it still remains a significant challenge to prepare various new fluorescent polymers by functionalization of nonfluorescent polymers. A nonfluorescent 1H,1H,2H,2H-perfluoro-1-decanol grafted to nonfluorescent polystyrene-b-poly(acrylic acid) block copolymers through simply esterification reaction can exhibit strong blue emission. On the basis of control experiments and theoretical simulation, we have proposed that the luminescence stems from interchain n → π* interaction between the lone pair (n) of hydroxyl O atoms of carboxyl units and empty π* orbital of ester carbonyl unit. In addition, the fluorescent polymers are successfully employed for fluorescence imaging in living HeLa cell. [ABSTRACT FROM AUTHOR]

Cysteine (Cys) is an essential amino acid and plays important roles in many biological processes. Bioluminescence (BL) is advantageous in sensitivity but BL probes that were intentionally developed for the selective detection of Cys were rarely reported. Herein, employing a fast conjugate addition between Cys and acrylic ester, we synthesized a caged BL probe acrylic ester luciferin (1) and used it to selectively detect Cys in vitro and image Cys in living cells and in tumor sites. We envision that, in the future, probe 1 might be used for evaluating the Cys roles in more biological processes. [ABSTRACT FROM AUTHOR]

Carboxyl-enriched and size-selected polymer nanoparticles (NPs) may prove to be very useful in biomedical applications for linker-free binding of biomolecules and their transport to cells. In this study, we report about the synthesis of such NPs by low-pressure low-temperature pulsed plasma polymerization of acrylic acid. Gas aggregation cluster source was adapted to operate plasma with a constant pulse period of 50 μs and with varying duty cycle. The NPs were produced with the size ranging from 31 ± 5 to 93 ± 14 nm and with retention of the carboxyl groups ranging from 4.0 to 12.0 atom %. Two regimes of the NP formation were identified. In the large duty cycle regime, the NP growth was interfered with by positive ion bombardment which resulted in the ion-driven detachment of the carboxyl species and in the formation of carboxyl-deficient NPs. In the small duty cycle regime, the NP growth was accompanied by the radical-driven chain propagation with the attachment of intact monomer molecules. Improved efficacy of the monomer retention resulted in increased concentration of the carboxyl groups. [ABSTRACT FROM AUTHOR]

Stimuli-responsive hydrogels represent a class of materials capable of reversibly switching their morphological and physicochemical characteristics. An ultrathin poly(acrylic acid) film (ca. 6 nm) grafted onto the gate of a p-type EGOFET is studied, and the correlation between the swelling state of the hydrogel and the transistor output characteristics is presented. The hydrogel-related swelling process occurring in basic medium causes an increase in threshold voltage due to the abrupt and intense increase of the negative charge density on the gate electrode. The variation of the drain current during the in situ modification of the pH electrolyte allows a quantitative analysis of the hydrogel switching kinetics. This work shows not only the relevance of EGOFET as an analytical tool in the broad sense, i.e., able to follow in real time phase transition processes of stimuli-responsive materials, but also the relevance of using a hydrogel for field-effect-based (bio)detection according to the ability of such material to overcome the well-known Debye length problematics. [ABSTRACT FROM AUTHOR]

Photoconductive cell of CdS was used to optimize the photograft polymerization of acrylic acid (AA) onto polypropylene film surface. Effect of UV-light intensity on the performance of this reaction in the three-dimensional space inside the reactor was researched. A relationship between light intensity measured as conductance and performance of the AA graft reaction was found. In addition, a linear relationship (r2 = 0.98) between the grafting degree (G) and conductance (G/wt% = (2.2 ± 0.1) 104c - (0.3 ± 0.4)) was determined in the range of 5 to 20% G, where a minimum stabilization time, such as 5 min, was required. Standard deviation of the G-value and the conductance decreased when a longer distance between the film and the lamp was used, leading to a more homogeneous surface modification. Therefore, we propose this system as a new method to monitor and predict the performance of UV-induced reactions. [ABSTRACT FROM AUTHOR]

Estrogen receptor α (ERα) is an important target for the design of drugs such as tamoxifen (2a) and fulvestrant (5). Three series of ER-ligands based on the benzoxepin scaffold structure were synthesized: series I containing an acrylic acid, series II with an acrylamide, and series III with a saturated carboxylic acid substituent. These compounds were shown to be high affinity ligands for the ER with nanomolar IC50 binding values. Series I acrylic acid ligands were generally ERα selective. In particular, compound 13e featuring a phenylpenta-2,4-dienoic acid substituent was shown to be antiproliferative and downregulated ERα and ERβ expression in MCF-7 breast cancer cells. Interestingly, from series III, the phenoxybutyric acid derivative compound 22 was not antiproliferative and selectively downregulated ERβ. A docking study of the benzoxepin ligands was undertaken. Compound 13e is a promising lead for development as a clinically relevant SERD, while compound 22 will be a useful experimental probe for helping to elucidate the role of ERβ in cancer cells. [ABSTRACT FROM AUTHOR]

We report a high-resolution electrospray ionization mass spectrometric (HR ESI-MS) access route leading to in-depth insights into the spontaneous zwitterionic copolymerization mechanism between cyclic imino ethers (i.e., 2-methyl-2-oxazoline (MeOx), 2-ethyl-2-oxazoline (EtOx), or 2-ethyl-2-oxazine (EtOz)) with acrylic acid (AA), exploiting the characteristic species accumulating during the copolymerization as well as tandem mass spectrometry (MS/MS). We demonstrate preferences in α,ω-end group formation by screening various feed ratios of cyclic imino ethers and acrylic acid (e.g., MeOx:AA = 1:1; MeOx:AA = 2:1; and MeOx:AA = 1:2). Critically, a calibration curve--based on AA-MeOx-AA dimer--was established allowing for the semiquantitative determination of the end-group ratios with different feed ratios of acrylic acid. The formation of previously suggested alternating copolymers was confirmed by MS/MS experiments. Deviations from an ideal alternating composition were found to decrease from MeOx to EtOx to EtOz. The results of (semiquantitative) HR ESI-MS and MS/MS measurements suggest, for the first time presented in such precision, a polymerization mechanism for the spontaneous zwitterionic (alternating) copolymerization indicating optimal monomer ratios and pairings. [ABSTRACT FROM AUTHOR]

The feasibility of employing reversible reactions to convert the separation of ethanediol (EG) and 1,2-butanediol (1,2-BDO) azeotropic system was analyzed in our previous work. This article aims at systematically screening the feasible reactants for the reaction-assisted separation process. A screening principle was brought up and applied. Through preliminary screening, acetic acid, acrylic acid, acetaldehyde, propionaldehyde, propanol, and butanone were obtained as potential reactants. Propionaldehyde was chosen as the proper one after fully comparing the reaction selectivity difference and conversion of EG and 1,2-BDO in the reaction process, the separation efficiency in the purification process, and final EG yield. The separation efficiency was predicted based on the relative volatility of EG, 1,2-BDO, and their corresponding products and was verified by distillation experiments. The stratification appeared in the reaction was found beneficial to the coupling of reaction and separation. [ABSTRACT FROM AUTHOR]

The rotational spectrum of acrylic sulfuric anhydride (CH2═CHCOOSO2OH, AcrSA) has been observed using pulsed-nozzle Fourier transform microwave spectroscopy. The species was produced from the reaction between acrylic acid and sulfur trioxide in a supersonic jet. Spectroscopic constants are reported for both the s-cis- and s-trans-AcrSA conformers of the parent and monodeuterated (OD) isotopologues. Geometries were optimized for both conformers using M06-2X/6-311++G(3df,3pd) methods. Single-point energy calculations at the M06-2X geometries were calculated using the CCSD(T)/complete basis set method with double and triple extrapolation [CBS(D-T)]. Further calculations indicate that the anhydride results from a π2 + π2 + σ2 cycloaddition reaction within the acrylic acid-SO3 complex. Because the C═O double bond of the acrylic acid migrates from one of the COOH oxygens to the other during the reaction, the s-cis form of acrylic acid leads to the s-trans form of the anhydride and vice versa. With zero-point energy corrections applied to the CCSD(T) energies, the s-cis and s-trans forms of CH2═CHCOOSO2OH are 19.0 and 18.8 kcal/mol lower in energy than that of SO3 + their corresponding CH2═CHCOOH precursor conformation. The zero-point-corrected transition state energies for formation of the s-trans and s-cis anhydrides are 0.22 and 0.33 kcal/mol lower than those of the complexes of SO3 with s-cis and s-trans acrylic acid, respectively, indicating that the reaction is essentially barrierless. This system adds to a growing body of examples demonstrating that carboxylic acids readily add to SO3 in the gas phase to produce the corresponding carboxylic sulfuric anhydride. [ABSTRACT FROM AUTHOR]

Pervaporation-based hybrid processes have been investigated to overcome the drawbacks of equilibrium-limited reactions. Pervaporation processes are strongly recommended for heat-sensitive products and azeotropic mixtures as in the butyl acrylate system case, since pervaporation can operate at lower temperatures than distillation. In this work, experimental pervaporation data for multicomponent mixtures in the absence of reaction were measured for the compounds involved in the esterification reaction of acrylic acid with n-butanol at different temperatures: 323, 353, and 363 K. A commercial tubular microporous silica membrane from Pervatech was used which is highly selective to water, and its performance was evaluated by studying several parameters, like the selectivity, permeate fluxes, driving force of species, and separation factor. The effects of temperature and feed composition were assessed for binary, ternary, and quaternary mixtures. Increasing the temperature increases significantly the total permeate flux as well as the separation factor, which is higher for quaternary mixtures. The presence of butyl acrylate and acrylic acid reduces the total permeate flux since these molecules hinder the water permeation. The permeance of each species was correlated with temperature according to the Arrhenius equation, and a mathematical model was proposed to develop an integrated reaction-separation process using the experimental data obtained. The reaction conversion of the fixed-bed membrane reactor at steady state achieved 98.7% at isothermal conditions, increasing by 66% the conversion obtained in a fixed-bed reactor (at the same operating conditions). [ABSTRACT FROM AUTHOR]

An efficient synthesis of disubstituted acrylic acids has been realized via Rh(III)-catalyzed C-H activation of (hetero)arenes and coupling with four-membered methyleneoxetanones under redox-neutral conditions. In most cases, the reactions are silver-free, and the products are exclusively E-selective with a broad substrate scope. The transformation proceeds via ortho C-H activation followed by selective olefin insertion and β-oxygen elimination. [ABSTRACT FROM AUTHOR]

Core-shell-corona silica/polymer hybrid nanoparticles with narrow size distribution were prepared in the template of spherical polyelectrolyte brushes (SPB) which consist of a solid polystyrene (PS) core densely grafted with linear poly(acrylic acid) (PAA) chains. The microstructure of obtained hybrid nanoparticles was studied by small-angle X-ray scattering (SAXS) and in combination with dynamic light scattering (DLS) and transmission electron microscopy (TEM). The generation of silica shell within the brush is confirmed by the significant increase of the electron density in the shell, and the silica shell showed a unique inner-loose-outer-dense structure, whose thickness is pH sensitive but is insensitive to ionic strength as revealed by fitting SAXS data. After dissolving the PS core, hollow silica nanoparticles were obtained and determined by SAXS, which should be ideal carriers for pH-triggered drug delivery. SAXS is confirmed to be a powerful method to characterize the core-shell-corona silica/polymer hybrid and hollow silica nanoparticles. [ABSTRACT FROM AUTHOR]

Thiolated poly(acrylic acid) (PAA-SH) functionalized gold nanoparticles were explored as a colloidal catalyst with potential application as a recoverable catalyst where the PAA provides pH-responsive dispersibility and phase transfer capability between aqueous and organic media. This system demonstrates complete nanoparticle recovery and redispersion over multiple reaction cycles without changes in nanoparticle morphology or reduction in conversion. The catalytic activity (rate constant) was reduced in subsequent reactions when recovery by aggregation was employed, despite unobservable changes in morphology or dispersibility. When colloidal catalyst recovery employed a pH induced phase transfer between two immiscible solvents, the catalytic activity of the recovered nanoparticles was unchanged over four cycles, maintaining the original rate constant and 100% conversion. The ability to recover and reuse colloidal catalysts by aggregation/redispersion and phase transfer methods that occur at low and high pH, respectively, could be used for different gold nanoparticle catalyzed reactions that occur at different pH conditions. [ABSTRACT FROM AUTHOR]

We investigate the phase behaviors of binary mixtures of polystyrene (PS) hard-sphere and poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM) soft-sphere colloidal particles as a function of temperature. As the temperature increases, apparent attractions arise between the PS particles, to the point of clustering at the highest temperature. This attractive force is found to be due to the change in pH caused by the acrylic acid co-polymerized with the temperature-sensitive PNIPAM particles, which in turn collapses the sterical stabilizing surface layers on the PS particles. Our experiments provide a new way to tune colloidal interactions with temperature for particles that are otherwise insensitive to temperature variations. [ABSTRACT FROM AUTHOR]

Catalytic dehydration of lactic acid in the presence of water is a potentially green, synthetic approach for the production of acrylic acid, and development of a highly selective catalyst is a primary challenge, leading to a resurgence in catalyst exploration and discovery. However, because the complexity in the analytical assessment of the efficiency of catalysts stemming from the possible presence of dimers in lactic acid feedstocks has often been neglected in the literature, we demonstrate, without consideration of the dimer during catalyst evaluation, that they can have a substantial influence on the determination of conversion of lactic acid and selectivity to acrylic acid in aqueous solution. In one example of a modified zeolite catalyst, a true acrylic acid of selectivity of 64% was overestimated to be 80% if the dimers in the feed solution were neglected in the analytical analysis. A survey of the literature demonstrated very few researchers account for the possible presence of lactic acid dimers in the lactic acid solution; therefore, the reported catalyst performance should be carefully considered in light of the potentially significant impact of lactic acid dimers. We further demonstrate that the heat treatment of a lactic acid feed solution prior to the reaction can hydrolyze dimers back to monomers, avoiding analytical misinterpretation and providing an accurate measure of the catalytic performance. [ABSTRACT FROM AUTHOR]

This work demonstrates that the photoinert trans-3-(2'-pyridyl)acrylic acid (2-PA) can be made photoreactive by salt formation with HCl, CF3CO2H, and H2SO4. All three salts undergo photodimerization in head-to-tail (HT) fashion resulting in the formation of the corresponding dimer, 2,4-bis(2'-pyridyl)-cyclobutane-1,3-dicarboxylic acid (HT-rctt-2,2'-BPCD), of which the former two salts, namely, [2-PAH]Cl·H2O and [(2-PAH)](CF3CO2) undergo single-crystal-to-single-crystal (SCSC) conversion. trans-3-(3'-Pyridyl)acrylic acid (3-PA), on the other hand, is known to be photoreactive and undergoes photodimerization in head-to-head (HH) fashion producing the dimer HH-rctt-3,3'-BPCD. The HH-orientation of 3-PA can be flipped to HT by forming the ClO4 - salt, which upon photodimerization produces HT-rctt-3,3'-BPCD. While HT-rctt-2,2'-BPCD exhibits isomerization in the presence of acid in solution, both the HH- and HT-rctt-3,3'-BPCD were inert under similar conditions. Our work demonstrates how the noncovalent intermolecular interactions can play a crucial role in the stereoselective synthesis and also emphasizes that the position of the nitrogen atom in the pyridyl ring is vital for the isomerization to occur in solution. [ABSTRACT FROM AUTHOR]

We explore the influence of a selective substrate on the composition and sequence statistics during the free radical copolymerization. In particular, we study the radical copolymerization of styrene and acrylic acid in bulk and in silica pores of different sizes. We show that the substrate affects both polymer composition and sequence statistics. We use dissipative particle dynamics simulations to study the polymerization process in detail, trying to pinpoint the parameters responsible for the observed differences in the polymer chain composition and sequences. The magnitude of the observed effect depends on the fraction of adsorbed monomer units, which cannot be described in the framework of the copolymerization theories based on the terminal unit model. [ABSTRACT FROM AUTHOR]

This study demonstrated the feasibility of using regenerable polyelectrolyte membranes to ultimately control the irreversible membrane fouling in a forward osmosis (FO) process. The regenerable membrane was fabricated by assembling multiple polyethylenimine (PEI) and poly(acrylic acid) (PAA) bilayers on a polydopamine-functionalized polysulfone support. The resulting membrane exhibited higher water flux and lower solute flux in FO mode (with the active layer facing feed solution) than in PRO mode (with the active layer facing draw solution) using trisodium citrate as draw solute, most likely due to the unique swelling behavior of the polyelectrolyte membrane. Membrane regeneration was conducted by first dissembling the existing PEI-PAA bilayers using strong acid and then reassembling fresh PEI-PAA bilayers on the membrane support. It was found that, after the acid treatment, the first covalently bonded PEI layer and some realigned PAA remained on the membrane support, acting as a beneficial barrier that prevented the acid-foulant mixture from penetrating into the porous support during acid treatment. The water and solute flux of the regenerated membrane was very similar to that of the original membrane regardless of alginate fouling, suggesting an ultimate solution to eliminating the irreversible membrane fouling in an FO process. With a procedure similar to the typical membrane cleaning protocol, in situ membrane regeneration is not expected to noticeably increase the membrane operational burden but can satisfactorily avoid the expensive replacement of the entire membrane module after irreversible fouling, thereby hopefully reducing the overall cost of the membrane-based water-treatment system. [ABSTRACT FROM AUTHOR]

Biomaterials for cell culture allowing simple and quantitative presentation of instructive cues enable rationalization of the interplay between cells and their surrounding microenvironment. Poly(acrylamide) (PAAm) hydrogels are popular 2D-model substrates for this purpose. However, quantitative and reproducible biofunctionalization of PAAm hydrogels with multiple ligands in a trustable, controlled, and independent fashion is not trivial. Here, we describe a method for bifunctional modification of PAAm hydrogels with thiol- and amine- containing biomolecules with controlled densities in an independent, orthogonal manner. We developed copolymer networks of AAm with 9% acrylic acid and 2% N-(4-(5-(methylsulfonyl)-1,3,4-oxadiazol-2-yl)phenyl)acrylamide. The covalent binding of thiol- and amine-containing chromophores at tunable concentrations was demonstrated and quantified by UV spectroscopy. The morphology, mechanical properties, and homogeneity of the copolymerized hydrogels were characterized by scanning electron microscopy, dynamic mechanical analysis, and confocal microscopy studies. Our copolymer hydrogels were bifunctionalized with polylysine and a laminin-mimetic peptide using the specific chemistries. We analyzed the effect of binding protocol of the two components in the maturation of cultured postmitotic cortical neurons. Our substrates supported neuronal attachment, proliferation, and neuronal differentiation. We found that neurons cultured on our hydrogels bifunctionalized with ligand-specific chemistries in a sequential fashion exhibited higher maturation at comparable culture times than using a simultaneous bifunctionalization strategy, displaying a higher number of neurites, branches, and dendritic filopodia. These results demonstrate the relevance of quantitative and optimized coupling chemistries for the performance of simple biomaterials and with sensitive cell types. [ABSTRACT FROM AUTHOR]

8-Azacoumarins have emerged as a promising class of compounds but are rarely explored due to challenging access. A novel, general, and practical method is provided for this class of compounds. The key lactonization step employs trans-acrylic acid attached pyridine N-oxides as the starting material, with acetic anhydride as both the activation agent and the solvent. Multiple transformations were involved in this reaction, including conjugate addition, nucleophilic aromatic substitution, and elimination. These studies provide the basis for access to 8-azacoumarins, enabling future work including the discovery and development of novel coumarin-type drugs, fluorescent probes, photolabile protecting groups, and other active molecules. [ABSTRACT FROM AUTHOR]

Polyelectrolyte complex (PEC) films made from oppositely charged polymer chains have applications as drug-delivery vehicles, separation membranes, and biocompatible coatings. Conventional layer-by-layer techniques for polyelectrolyte coatings are low-throughput and multistep processes that are quite slow for building films on the order of micrometers. In this work, PEC films are electrochemically deposited using a rapid one-pot method, yielding thick (1 μm) films within short experimental time scales (5 min). This rapid electrodeposition is achieved by exploiting the reduction of hydrogen peroxide at mild electrode potentials that avoid water electrolysis yet trigger the pH-responsive self-assembly of a PEC film composed of poly(acrylic) acid and poly(allylamine) HCl. In situ rheology using an electrochemical quartz crystal microbalance quantified the shear modulus-density product of the deposited layer to be on the order of 107 Pa g/cm3 at a frequency of 15 MHz, with a viscoelastic phase angle of approximately 50°. This electrodeposition scheme furthers the development of PEC coatings for more high-throughput applications, where a fast and efficient single-step approach would be desirable for obtaining coatings. [ABSTRACT FROM AUTHOR]

It is challenging to develop hydrogels with a combination of excellent mechanical properties, versatile functions, and good processability. Here we report a physical hydrogel of poly(acrylamide-co-acrylic acid) (P(AAm-co-AAc)) cross-linked by carboxyl-Fe3+ coordination complexes that possesses high stiffness and toughness, fatigue resistance, and stimulation-triggered healing along with shape memory and processing abilities. The copolymers have randomly dispersed AAm and AAc repeat units, making the physical cross-links with different strength. The strong coordination bonds and their associations serve as permanent cross-links, imparting the elasticity, whereas the weak ones reversibly rupture and re-form, dissipating the energy. Furthermore, a stick-slip instability is observed during the tearing test, which should be associated with the specific nature of metal-coordination bonds that are strong yet fragile. Because of the dynamic nature of coordination bonds, both tensile and tearing mechanical properties are rate dependent. By tuning the bond strength via pH, the gels show distinct mechanical properties, shape memory ability, and even reversible sol-gel transition. The system also shows good processability; the copolymer solutions can be processed into tough gels with different structures by three-dimensional printing technology. These versatile, tough, yet processable hydrogels should be a promising material as structural elements in various applications. [ABSTRACT FROM AUTHOR]

Melt state dynamics for a series of strictly linear polyethylenes with precisely spaced associating functional groups were investigated. The periodic pendant acrylic acid groups form hydrogen-bonded acid aggregates within the polyethylene (PE) matrix. The dynamics of these nanoscale heterogeneous morphologies were investigated from picosecond to nanosecond timescales by both quasi-elastic neutron scattering (QENS) measurements and fully atomistic molecular dynamics (MD) simulations. Two dynamic processes were observed. The faster dynamic processes which occur at the picosecond timescales are compositionally insensitive and indicative of spatially restricted local motions. The slower dynamic processes are highly composition dependent and indicate the structural relaxation of the polymer backbone. Higher acid contents, or shorter PE spacers between pendant acid groups, slow the structural relaxation timescale and increase the stretching parameter (β) of the structural relaxation. Additionally, the dynamics of specific hydrogen atom positions along the backbone correlate structural heterogeneity imposed by the associating acid groups with a mobility gradient along the polymer backbone. At time intervals (<2 ns), the mean-squared displacements for the four methylene groups closest to the acid groups are up to 10 times smaller than those of methylene groups further from the acid groups. At longer timescales acid aggregates rearrange and the chain dynamics of the slow, near-aggregate regions and the faster bridge regions converge, implying a characteristic timescale for the passage of chains between aggregates. The characterization of the nanoscale chain dynamics in these associating polymer systems both provides validation of simulation force fields and provides understanding of heterogeneous chain dynamics in associating polymers. [ABSTRACT FROM AUTHOR]

Iron oxide (IO)-based composite latex particles with a patchy IO overlayer were successfully prepared by Pickering emulsion polymerization of acrylic monomers and/or styrene using acrylic acid or methacrylic acid as auxiliary comonomers. The ultrasmall IO particles adsorbed at the latex surface and played the role of a solid stabilizer. The influence of the synthesis conditions on the composite particle size, polymerization kinetics, IO incorporation efficiency, and particle morphology was studied. Thermogravimetric analysis indicated that the efficiency of iron oxide incorporation was improved with increasing the suspension pH, the amount of auxiliary comonomer, or the IO content and reached ca. 90% under optimized conditions. Reducing the initial iron oxide concentration at constant monomer concentration led to an increased particle size and a reduced colloid stability, indicating that the magnetic nanoparticles stabilized the colloidal nanocomposites. Transmission electron microscopy studies confirmed the presence of iron oxide at the particle surface. In light of these results, a tentative mechanism for Pickering emulsion polymerization using IO nanoparticles as solid stabilizer in the presence of (meth)acrylic acid auxiliary comonomers was proposed. [ABSTRACT FROM AUTHOR]

We demonstrate a robust and tunable micromolding method to fabricate chemically functional poly(acrylamide-co-acrylic acid) (p(AAm-co-AA)) hydrogel microspheres with uniform dimensions and controlled porous network structures for rapid biomacromolecular conjugation. Specifically, p(AAm-co-AA) microspheres with abundant carboxylate functional groups are fabricated via surface-tension-induced droplet formation in patterned poly(dimethylsiloxane) molds and photoinduced radical polymerization. To demonstrate the chemical functionality, we enlisted rapid EDC/NHS (1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS)) chemistry for fluorescent labeling of the microspheres with small-molecule dye fluorescein glycine amide. Epifluorescence imaging results illustrate the uniform incorporation of carboxylate groups within the microspheres and rapid conjugation kinetics. Furthermore, protein conjugation results using red fluorescent protein R-phycoerythrin demonstrate the highly porous nature of the microspheres as well as the utility of the microspheres and the EDC/NHS scheme for facile biomacromolecular conjugation. Combined, these results illustrate the significant potential for our fabrication-conjugation strategy in the development of biofunctionalized polymeric hydrogel microparticles toward rapid biosensing, bioprocess monitoring, and biodiagnostics. [ABSTRACT FROM AUTHOR]

Aqueous mixtures of pH-sensitive block random BAB triblock copolymers with different hydrophobic B blocks connected to the same hydrophilic A block were studied in order to investigate comicellization and the impact on the dynamic mechanical properties. The B blocks were statistical copolymers of acrylic acid (AA) and n-butyl acrylate (nBA) with varying AA contents, whereas the A block was a pure PAA. Neat triblocks self-assembled into transient networks for which the mechanical relaxation time depended both on the AA content within the B blocks and on the pH, which affected the ionization of the AA units. Static and dynamic light scattering measurements were done on mixtures of equivalent AB diblock copolymers that showed that comicellization occurred only at conditions at which both copolymers considered separately self-assemble. When comicellization occurred, the characteristic escape time of both types of B blocks from the mixed hydrophobic cores impacted the rheological properties of the binary triblock mixture. Using binary mixtures of BAB triblock copolymers exhibiting pH-controlled dynamics thus allows control and fine-tuning of the viscoelastic properties at constant pH by formulation without the need to synthesize a large number of different polymers. Moreover, the more dynamic B blocks were slowed down in the presence of the less dynamic ones, and vice versa, so that a frozen network could be transformed into a transient one by coassembly with very dynamic chains. [ABSTRACT FROM AUTHOR]

A universal mold casting approach for the preparation of cation-exchange membranes (CEMs) and anion-exchange membranes (AEMs) with ultrahigh ion-exchange capacities (IECs) is developed based on in situ cross-linking polymerization of acrylic acid (AA) and 2-vinylpyridine (2VP), respectively. This new method produced ultrahigh IECs of 7.88 mequiv g-1 for CEM and 6.27 mequiv g-1 for AEM, which are 8.8 and 7.0 times that (0.89 mequiv g-1) of Nafion 117, respectively. Also, the prepared membranes demonstrate excellent thermal and chemical stability and acceptable conductivity. As a consequence, the membranes show relatively high performance for ion-exchange application and methanol barrier, exhibiting ion permeabilities of 2.06 × 10-7 cm² s-1 for Na+, 2.57 × 10-7 cm² s-1 for Ca2+, 1.45 × 10-7 cm² s-1 for Cu2+ regarding CEMs, and 7.72 × 10-7 cm² s-1 for methanol regarding AEMs. These results indicate that the CEMs and AEMs fabricated from the universal mold casting approach are promising candidates for targeting ultrahigh ion-exchange capacity membranes. [ABSTRACT FROM AUTHOR]

Chemical cross-linking of layer-by-layer assembled films promotes mechanical stability and robustness in a wide variety of environments, which can be a challenge for polyelectrolyte multilayers in saline environments or for multilayers made from weak polyelectrolytes in environments with extreme pHs. Heating branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA) multilayers at sufficiently high temperatures drives amidization and dehydration to covalently cross-link the film, but this reaction is rather slow, typically requiring heating for hours for appreciable cross-linking to occur. Here, a more than one order of magnitude increase in the amidization kinetics is realized through microwave heating of BPEI/PAA multilayers on indium tin oxide (ITO)/glass substrates. The cross-linking reaction is tracked using infrared spectroscopic ellipsometry to monitor the development of the cross-linking products. For thick films (∼1500 nm), gradients in cross-link density can be readily identified by infrared ellipsometry. Such gradients in cross-link density are driven by the temperature gradient developed by the localized heating of ITO by microwaves. This significant acceleration of reactions using microwaves to generate a well-defined cross-link network as well as being a simple method for developing graded materials should open new applications for these polymer films and coatings. [ABSTRACT FROM AUTHOR]

Double network hydrogels (DN gels) are considered as one of the toughest soft materials. However, conventional chemically linked DN gels often lack high self-recovery and fatigue resistance properties due to permanent damage of covalent bonds upon deformation. Current strategies to improve self-recovery and fatigue resistance properties of tough DN gels mainly focus on the manipulation of the first network structure. In this work, we proposed a new design strategy to synthesize a new type of Agar/PAMAAc-Fe3+ DN gels, consisting of an agar gel as the first physical network and a PAMAAc-Fe3+ gel as the second chemical-physical network. By introducing Fe3+ ions into the second network to form strong coordination interactions, at optimal conditions, Agar/PAMAAc-Fe3+ DN gels can achieve extremely high mechanical properties (σf of ∼8 MPa, E of ∼8.8 MPa, and W of ∼16.7 MJ/m³), fast self-recovery (∼50% toughness recovery after 1 min of resting), and good fatigue resistance compared to properties of cyclic loadings by simply controlling acrylic acid (AAc) content in the second network. The high toughness and fast recovery of Agar/PAMAAc-Fe3+ DN gel is mainly attributed to energy dissipation through reversible noncovalent bonds in both networks (i.e., hydrogen bonds in the agar network and Fe3+ coordination interactions in the PAMAAc network). The time-dependent recovery of Agar/PAMAAc-Fe3+ gels at room temperature and the absence of recovery in Agar/PAMAAc gels also confirm the important role of Fe3+ coordination interactions in mechanical strength, self-recovery, and fatigue resistance of DN gels. Different mechanistic models were proposed to elucidate the mechanical behaviors of different agar-based DN gels. Our results offer a new design strategy to improve strength, self-recovery, and fatigue resistance of DN gels by controlling the structures and interactions in the second network. We hope that this work will provide an alterative view for the design of tough hydrogels with desirable properties. [ABSTRACT FROM AUTHOR]

An in situ NMR technique is used to measure the relative monomer consumption rates of acrylamide (AM) and acrylic acid (AA) over a broad range of initial comonomer compositions, initial monomer concentrations (5-40 wt % in aqueous solution), and the complete range of AA ionization. The composition drift with conversion was found not only to be a strong function of AA ionization but also to vary systematically with monomer concentration, with the latter influence increasing at increased degrees of ionization. The coupled effect is captured by expressions developed to represent the monomer reactivity ratios as a function of these two major variables. The proposed correlation, easily implemented into any modeling framework, is based on experimentally measured composition over a much broader range of conditions than examined in previous studies and accurately captures the effect of monomer concentration at low and high degrees of ionization. [ABSTRACT FROM AUTHOR]

Poly(acrylic acid) with grafted TEMPO moieties, PAA-T, phase separates over the pH range 2-4, whereas at lower and higher pH, the polymer is water-soluble. The pH range of the two-phase region increases linearly with the content of grafted TEMPO moieties. As evidenced by surface tension measurements, the PAA-T molecules have little hydrophobic character. We propose that at low pH PAA-T is an amphoteric polymer that, in addition the anionic carboxyl groups, contains cationic species resulting from the disproportion of TEMPO at low pH. Furthermore, we propose that two-phase regions occur near the isoelectric points of the polymer, suggesting that phase separation is due to electrostatically driven association of polymer molecules. [ABSTRACT FROM AUTHOR]

Two polymorphic forms of (Z)-3-bromopropenoic acid are reported. Form I (monoclinic, P21/c) with Z' = 1 is obtained from a range of solvents, while Form II (monoclinic, P21/n) with Z' = 4 can be prepared only from either benzene or toluene. Both forms are isolated at room temperature. The molecules in both polymorphs interact with one another through similar dominant hydrogen bonding motifs; however, the packing arrangement differs in the prevalence of weaker hydrogen bonds in the metastable Form II. Analysis of this high and low Z' polymorphic pair using differential scanning calorimetry, grinding and slurry experiments, coupled with lattice energy calculations suggests that the low Z' Form I is the most stable under ambient conditions. Two-dimensional fingerprint plots derived from Hirshfeld surfaces highlight the more extensive hydrogen bonding in Form II, while Form I is more densely packed. This polymorphic pair may be a candidate for the role of solution preaggregation in the formation of high Z' forms. [ABSTRACT FROM AUTHOR]

The cooperative self-assembly of amphiphilic polystyrene-block-poly(acrylic acid) (PS144-b-PAA22) and polystyrene-block-poly(4-vinylpyridine) (PS144-b-P4VP33) diblock copolymers in DMF/H2O mixtures has been investigated. Both copolymers self-assemble into small spherical micelles (SSMs) if used individually. However, the equimolar mixture of these two copolymers cooperatively self-assembles into vesicles. It is found that the formation of vesicles is attributed to the complex interactions between PAA and P4VP chains, including the hydrogen bonds between un-ionized acrylic acid units and pyridine units as well as the electronic attractions between ionized acrylic acid units and protonated pyridine units. Since these interactions between PAA and P4VP chains depend on pH value, the cooperatively self-assembled morphology can be easily tuned by the addition of HCl or NaOH. At high addition of H+ or OH-, the intercorona interaction is repulsive and the copolymer mixture tends to form SSMs (basic condition) or cylindrical micelles (acidic condition), whereas it prefers to aggregate into vesicles at low addition of H+ or OH- because the intercorona interaction is attractive. Interestingly, the same morphology of the self-assembled aggregates can be obtained either at high H+ addition or at low OH- addition, which results from the nonmonotonic variation of the intercorona interaction along with the addition of HCl or NaOH. The current study implies that it is the intercorona interaction rather than the chemical condition that dominates the cooperatively self-assembled morphology. [ABSTRACT FROM AUTHOR]

Stimuli-responsive soft materials are a highly studied field due to their wide-ranging applications; however, only a small group of these materials display hysteretic responses to stimuli. Moreover, previous reports of this behavior have typically shown it to be short-lived. In this work, poly(acrylic acid) (PAA) chains at extremely high grafting densities and confined in nanoscale pores displayed a unique long-lived hysteretic behavior caused by their ability to form a metastable hydrogen bond network. Hydraulic permeability measurements demonstrated that the conformation of the PAA chains exhibited a hysteretic dependence on pH, where different effective pore diameters arose in a pH range of 3 to 8, as determined by the pH of the previous environment. Further studies using Fourier transform infrared (FTIR) spectroscopy demonstrated that the fraction of ionized PAA moieties depended on the thin film history; this was corroborated by metal adsorption capacity, which demonstrated the same pH dependence. This hysteresis was shown to be persistent, enduring for days, in a manner unlike most other systems. The hypothesis that hydrogen bonding among PAA units contributed to the hysteretic behavior was supported by experiments with a urea solution, which disrupted the metastable hydrogen bonded state of PAA toward its ionized state. The ability of PAA to hydrogen bond within these confined pores results in a stable and tunable hysteresis not previously observed in homopolymer materials. An enhanced understanding of the polymer chemistry and physics governing this hysteresis gives insight into the design and manipulation of next-generation sensors and gating materials in nanoscale applications. [ABSTRACT FROM AUTHOR]

Plasma polymerization is traditionally recognized as a homogeneous film-forming technique. It is nevertheless reasonable to ask whether micrometer thick plasma polymerized structures are really homogeneous across the film thickness. Studying the properties of the interfacial, near-the-substrate (NTS) region in plasma polymer films represents particular experimental challenges due to the inaccessibility of the buried layers. In this investigation, a novel non-destructive approach has been utilized to evaluate the homogeneity of plasma polymerized acrylic acid (PPAc) and 1,7-octadiene (PPOD) films in a single measurement. Studying the variations of refractive index throughout the depth of the films was facilitated by a home-built surface plasmon resonance (SPR)/optical waveguide (OWG) spectroscopy setup. It has been shown that the NTS layer of both PPAc and PPOD films exhibits a significantly lower refractive index than the bulk of the film that is believed to indicate a higher concentration of internal voids. Our results provide new insights into the growth mechanisms of plasma polymer films and challenge the traditional view that considers [ABSTRACT FROM AUTHOR]

Asymmetric hydrogenation of various α-substituted acrylic acids was carried out using RuPHOX-Ru as a chiral catalyst under 5 bar H2, affording the corresponding chiral α-substituted propanic acids in up to 99% yield and 99.9% ee. The reaction could be performed on a gram-scale with a relatively low catalyst loading (up to 5000 S/C), and the resulting product (97%, 99.3% ee) can be used as a key intermediate to construct bioactive chiral molecules. The asymmetric protocol was successfully applied to an asymmetric synthesis of dihydroartemisinic acid, a key intermediate required for the industrial synthesis of the antimalarial drug artemisinin. [ABSTRACT FROM AUTHOR]

Poly(vinylphosphonic acid-co-acrylic acid) (PVPA-co-AA) has recently been identified as a possible candidate for use in bone tissue engineering. It is hypothesized that the strong binding of PVPA-co-AA to calcium in natural bone inhibits osteoclast activity. The free radical polymerization of acrylic acid (AA) with vinylphosphonic acid (VPA) has been investigated with varying experimental conditions. A range of copolymers were successfully produced and their compositions were determined quantitatively using 31P NMR spectroscopy. Monomer conversions were calculated using 1H NMR spectroscopy and a general decrease was found with increasing VPA content. Titration studies demonstrated an increase in the degree of dissociation as a function of VPA in the copolymer. However, a VPA content ca. 30 mol % was found to be the optimum for calcium chelation, suggesting that this composition is the most promising for biomaterials applications. Assessment of cell metabolic activity showed that PVPA-co-AA has no detrimental effect on cells, regardless of copolymer composition. [ABSTRACT FROM AUTHOR]

The structures of imogolite-poly(acrylic acid) hydrogels were investigated using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) to determine the effects of particle concentration and the magnitude of deformation. The imogolite-poly(acrylic acid) hydrogel was synthesized by using γ-ray radiation as a nanocomposite gel with chemical bonds between the particles and polymers. The SAXS measurements revealed that the imogolite network was composed of particle overlaps. Under deformation, the gel structure was rearranged to increase the dimensionality of the network, forming a relaxed structure of overlaps by changing the orientation of the imogolite. The structural response of the deformed gel depended on the imogolite concentration, which influenced the changes in dimensionality of the network and the number of overlaps. The SANS patterns indicated that the polymers wrapped the imogolite aggregates, allowing polymers to follow the imogolite behavior. These observations demonstrate that the behavior of the imogolite can contribute to both the relaxation of stress and maintenance of the structure during an applied strain. [ABSTRACT FROM AUTHOR]