PAAc Chains Research Articles

Gelation of acrylic acid with Ag+ and conversion to Ag nanoparticle as potential system for biomedical applications

Silver (Ag) has been used to cross-link poly (acrylic acid) (PAAc) to obtain antibacterial nanocomposite hydrogel for controlled drug delivery systems. Ag+/PAAc composite hydrogel was prepared by free radical aqueous polymerization of acrylic acid (AAc) using potassium persulfate (KPS) as the initiator in the presence of silver nitrate (AgNO3). Sodium borohydride (NaBH4) was used to reduce the Ag ions present within the hydrogel matrix to generate Ag nanoparticles (Ag NPs). Transmission electron microscopy (TEM) characterization of the sample indicated the formation of Ag nanoparticles that distributed uniformly in the PAAc networks. UV–visible spectrophotometry showed an absorption peak at 425 nm that attribute to the well-known surface Plasmon resonance of the Ag bound in NPs. X-ray diffraction (XRD) pattern showed the appearance of some peaks corresponding to the face-centered cubic (f.c.c.) Ag phase. Energy dispersive spectroscopy (EDS) studies revealed that Ag NPs are successfully formed inside the Ag+/PAAc composite hydrogel. The gelation and crosslinking of PAAc chains with Ag+ by strong interactions between Ag cations and polyanions, deprotonated carboxylic groups of PAAc were identified from the Fourier transform infrared (FTIR) spectrogram. Field emission scanning electron microscopy (FESEM) exhibited an interconnected porous structure with an average pore size of about 10 μ for composite hydrogel that can absorb 440 g water/g dried sample. Dried samples were also loaded with amoxicillin and antibiotic release was studied. The antimicrobial activity of the Ag+ and Ag-NPs hydrogels was tested against Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa and Escherichia coli.

Controlling the electrostatic interaction using a thermal signal to structurally change thermoresponsive nanoparticles

The negatively charged thermoresponsive polymers poly(benzyl methacrylate)-b-poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PBzMA-b-PAAc-b-PIPAAm) were prepared by reversible-addition fragmentation chain transfer polymerization. The polymer formed core-shell polymeric micelles possessing a thermoresponsive corona composed of PAAc-b-PIPAAm below the lower critical solution temperature (LCST) of the PIPAAm chain. The nonionic thermoresponsive polymeric micelle composed of PBzMA-b-PIPAAm exhibited extensive inter-micellar aggregation after the hydrophobic phase transition of the corona-forming PIPAAm chains. In contrast, insertion of the PAAc chain into the thermoresponsive micelle maintained its dispersibility above the LCST of PIPAAm because of the electrostatic repulsion between the micelles. The micelles with short PAAc chains suppressed the effect of the negative charge derived from PAAc below the LCST because of the extended PIPAAm chain on the micellar surface. In contrast, the negative charge property appeared due to collapse of the PIPAAm layer above the LCST. This thermoresponsive change in its electrostatic behavior enables the micelle to control the adsorption and desorption of oppositely charged molecules in response to the temperature change across the LCST.

Agar/PAAc-Fe3+ hydrogels with pH-sensitivity and high toughness using dual physical cross-linking

As promising structural materials, various tough hydrogels have been developed recently by incorporating various kinds of bonds. An important challenge is to use dual physical cross-linking to develop both toughness and self-recovery in a single material. Here we report smart, strain-responsive hydrogels composed of a fully physically linked agarose/poly(acrylic acid)-ferric ion (agar/PAAc-Fe3+) double network (DN) with high toughness and pH-sensitivity. These hydrogels were fabricated in a one-pot reaction to generate dual physical cross-linking through, first, a hydrogen-bonded cross-linked agarose network, and, second, a physically linked PAAc-Fe3+ network via Fe3+ coordination interactions. The DN hydrogels possessed high toughness, with breaking strain of 1130%, fast self-recovery properties in ambient conditions (100% recovery in 30 min) and self-healing properties (the healed hydrogels can be manually stretched up to 700% of their original length after self-healing for 60 h from the cut-off state). In addition, the hydrogels exhibited pH-sensitivity due to the dissociation of ionic coordinate bonds between –COO− ions of the PAAc chains and Fe3+ ions. Double-layer hydrogel strips with two different concentrations of PAAc formed a “C”-shaped material when initially immersed in pH 7 solution and then soaked in a pH 3 solution. These characteristics make the hydrogels attractive candidates for tissue engineering, soft actuators and flexible electronics.

Multiamine-induced self-healing poly (Acrylic Acid) hydrogels with shape memory behavior

In this work, a versatile and simple strategy for building self-healing hydrogels with tunable mechanical properties and shape memory behavior is reported. A commercially available small molecule with three amino groups, diethylenetriamine (DETA), is applied to crosslink poly (acrylic acid) (PAAc) chains via ionic bonding, and the complexes of the PAAc chains with DETA form hydrophobic microdomains in the hydrogel network. The cooperation of ionic bonding and hydrophobic interactions drastically improves the mechanical properties, which can be modulated by adjusting the molar ratio of PAAc to DETA. Due to the physical interaction of the crosslinks, the hydrogels can self-heal rapidly in ambient conditions. The thermal responsiveness of the physical microdomain crosslinks endow the hydrogels with shape memory behavior. It is hoped that this novel strategy will provide new opportunities for the design of high-strength hydrogels with variable functionalities for a wide range of applications, such as artificial muscle and skin. A versatile and simple strategy for building self-healing hydrogels with tunable mechanical properties and shape memory behavior has been developed using diethylenetriamine to crosslink polyacrylic acid chains. Hydrophobic domains form in the network in addition to ionic bonds between the amino and carboxylic acid groups. The combination of ionic bonds and hydrophobic interactions not only provides self-healing ability but also drastically improves the strength.

Surface modification of polydimethylsiloxane elastomer for stable hydrophilicity, optical transparency and film lubrication

The surface of polydimethylsiloxane (PDMS) elastomer was hydrophilized by poly(acrylic acid) (PAAc) using Surface Initiated Atomic Transfer Radical Polymerization (Si-ATRP). The ATRP initiator chosen was ((Chloromethyl) phenylethyl) trichlorosilane, which was immobilized on the surface of the PDMS through a simple but innovative method of drop coating, in contrast to the commonly used vapor deposition and solution-immersion methods. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS) were employed to examine surface properties of modified PDMS and confirmed presence of the PAAc chains covalently bonded to the PDMS surface. Physical properties and topography of the modified sample were characterized by water contact angle measurement and Atomic Force Microscopy. It is shown that the drop-coating of the silane initiator for ATRP modification with PAAc can result in good surface hydrophilization while causing minimum damage to the PDMS preserving its desired optical transparency. The resultant hydrophilic PDMS is stable in air and has film lubrication behavior in aqueous conditions and may be used in the development of advanced microfluidic devices and sensors where both surface hydrophilicity and bulk transparency are desired.

Fabricating antigen recognition and anti-bioadhesion polymeric surface via a photografting polymerization strategy

A polymeric platform for immunodiagnostic bioassay was constructed based on biostable polymeric support and two functional monomers, low-fouling methacryloyloxyethyl phosphorylcholine (MPC) and acrylic acid (AAc), by a photografting polymerization approach. Covalent binding of antibody to pAAc chains was achieved by activating carboxyl with NHS/EDC partner. The resultant surface showed obvious suppression of nonspecific protein adsorption and platelet adhesion relative to the control sample, exhibiting good anti-bioadhesion performances. Based on the polymer-supported matrix, a highly sensitive antibody–antigen specific recognition was confirmed in both native plasma and diluted human plasma due to the enhanced antibody loading capacity and lowered bioadhesion as compared to the reference.

Thermo- and pH-responsive polypropylene microporous membrane prepared by the photoinduced RAFT-mediated graft copolymerization

Thermo- and pH-responsive polypropylene microporous membrane prepared by photoinduced reversible addition–fragmentation chain transfer (RAFT) graft copolymerization of acrylic acid and N-isopropyl acrylamide by using dibenzyltrithiocarbonate as a RAFT agent. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FT-IR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM) were used to characterize the structural and morphological changes on the membrane surface. Results of ATR/FT-IR and XPS clearly indicated that poly(acrylic acid) (PAAc) and poly(N-isopropyl acrylamide) (PNIPAAm) were successfully grafted onto the membrane surface. The grafting chain length of PAAc on the membrane surface increased with the increase of UV irradiation time, and decreased with the increase of the concentration of chain transfer agent. The PAAc grafted membranes containing macro-chain transfer agents, or the living membrane surfaces were further functionalized via surface-initiated block copolymerization with N-isopropyl acrylamide in the presence of free radical initiator, 2,2′-azobisisobutyronitrile. It was found that PNIPAAm can be grafted onto the PAAc grafted membrane surface. The results demonstrated that polymerization of AAc and NIPAAm by the RAFT method could be accomplished under UV irradiation and the process possessing the living character. The PPMMs with PAAc and PNIPAAm grafting chains exhibited both pH- and temperature-dependent permeability to aqueous media.

Double-Hydrophilic Block Copolymers Forming Intramolecular Polycomplexes

Double-hydrophilic block copolymers containing the charged blocks of poly(acrylic acid) (PAAc) and the neutral blocks of monomethyl ether of poly(ethylene oxide) (MEPEO) are synthesized by a free radical block copolymerization of PAAc with monomethyl ether of poly(ethylene glycol) of various molecular weights (M vMEPEG = 1.1·103 – 5·103). It is revealed that the block copolymerization has a matrix character because non-covalent interactions of propagating PAAc chains with MEPEG. This fact points out the formation of intramolecular polycomplexes in the given diblock copolymers. The MEPEO-b-PAAc copolymers obtained are characterized by 1H NMR spectroscopy.

Characterization of UV-Induced Graft Polymerization of Poly(acrylic acid) Using Optical Waveguide Spectroscopy

UV-induced graft polymerization is a simple and effective method for the surface modification and functionalization of polymeric materials. The structure of poly(acrylic acid) (PAAc) grafted onto a polymeric surface by UV-induced graft polymerization of acrylic acid was investigated using optical waveguide spectroscopy (OWS). The PAAc graft layer exhibited a large increase in thickness in water compared to that in the dry state due to the swellability of the PAAc chains. Its thickness further increased with increasing the pH of the aqueous solution. This could be attributed to the increased electrostatic repulsion of the carboxylate anions on the PAAc chains, as the ionization degree of the carboxylic groups increases with pH. The thickness of the PAAc graft layer is dependent on the graft condition employed, including the UV intensity and irradiation time, and the AAc monomer concentration. On the basis of these data, we propose a model for the structure of the PAAc graft layer and a PAAc layer modified by galactose ligands.

Preparation and characterization of polyacrylic acid‐poly(vinyl alcohol)‐based interpenetrating hydrogels

AbstractSome structural features of hydrogels from poly(acrylic acid) (PAAc) of various crosslinking degrees have been investigated through mechanical and swelling measurements. Interpenetrating polymer hydrogels (IPHs) of poly(vinyl alcohol) (PVA) and PAAc have been prepared by a sequential method: crosslinked PAAc chains were formed in aqueous solution by crosslinking copolymerization of acrylic acid and N,N‐methylenebisacrylamide in the presence of PVA. The application of freeze–thaw (F–T) cycles leads to the formation of a PVA hydrogel within the synthesized PAAc hydrogel. The swelling and viscoelastic properties of the IPHs were evaluated as a function of the content of crosslinker and the application of one F–T cycle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5789–5794, 2006

Synthesis and Temperature-Responsive Properties of Novel Semi-interpenetrating Polymer Networks Consisting of a Poly(acrylamide) Polymer Network and Linear Poly(acrylic acid) Chains

A novel semi-interpenetrating polymer network (semi-IPN) gel consisting of an AAm gel and linear PAAc chains was designed and developed. The semi-IPN gel was simply prepared by infiltrating PAAc chains into AAm gel networks from an outer PAAc solution through immersion of AAm gels in the PAAc solution. The semi-IPN gel swelled at higher temperature and shrunk at lower temperature. Swelling-ratio transition temperatures of the semi-IPN gel shifted to lower values with increasing pH of the surrounding PAAc solution. The swelling-ratio transition of the semi-IPN gel became sharper with higher-molecular-weight PAAc. These swelling-ratio changes were completely reversible. A prototype of a light modulator was fabricated utilizing semi-IPN microgel particles containing 20 wt % of carbon black pigment. The transmittance of the light modulator was altered from 63 to 8% when the light modulator was heated from 10 to 60 °C.

Poly(vinyl alcohol)–poly(acrylic acid) interpenetrating networks. Study on phase separation and molecular motions

We report on the preparation and characterization of interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) formed by a sequential method. Interpolymer interactions were examined using 13C CP/MAS NMR and DSC methods. Evidence on the formation of a PVA–PAAc complex through hydrogen bonds between the hydroxyl groups of the PVA chains and the carbonyl group of the PAAc chains was obtained. The existence of polymer interactions between PVA and PAAc and its effect on the molecular motion of polymer chains, was further investigated by means of the analysis of the 13C spin–lattice relaxation times in the rotating frame, T 1 ρ C . To elucidate the scale of the mixing in the PVA/PAAc IPNs, proton spin–lattice relaxation times in the rotating frame, T 1 ρ H , were also investigated. The analysis of the results reveals the compatibility between the PVA and the PAAc polymer networks at low PVA concentrations and the occurrence of phase separation at relatively high PVA concentrations.

Preparation and Characterization of Interpenetrating Polymer Hydrogels Based on Poly(acrylic acid) and Poly(vinyl alcohol)

AbstractInterpenetrating polymer hydrogels (IPHs) of Poly (vinyl alcohol) (PVA) and Poly (acrylic acid) (PAAc) have been prepared by a sequential method: crosslinked PAAc chains were formed in aqueous solution by crosslinking copolymerization of acrylic acid and N, N′‐methylenebisacrylamide in the presence of PVA. The application of freezing‐thawing cycles (F‐T cycles) leads to the formation of a PVA hydrogel within the synthesized PAAc hydrogel. The swelling and the viscoelastic properties of the prepared IPHs were evaluated on the basis of the structural features obtained from solid state 13C‐NMR spectroscopy.

Control of pore size and permeability of a glucose-responsive gating membrane for insulin delivery

The pore size and permeability control of a glucose-responsive gating membrane with plasma-grafted poly(acrylic acid) (PAAC) gates and covalently bound glucose oxidase (GOD) enzymes were investigated systematically. The PAAC-grafted porous polyvinylidene fluoride (PVDF) membranes with a wide range of grafting yields were prepared using a plasma-graft pore-filling polymerization method, and the immobilization of GOD was carried out by a carbodiimide method. The linear grafted PAAC chains in the membrane pores acted as the pH-responsive gates or actuators. The immobilized GOD acted as the glucose sensor and catalyzer; it was sensitive to glucose and catalyzed the glucose conversion to gluconic acid. The experimental results showed that the glucose responsivity of the solute diffusional permeability through the proposed membranes was heavily dependent on the PAAC grafting yield, because the pH-responsive change of pore size governed the glucose-responsive diffusional permeability. It is very important to design a proper grafting yield for obtaining an ideal gating response. For the proposed gating membrane with a PAAC grafting yield of 1.55%, the insulin permeation coefficient after the glucose addition (0.2 mol/l) was about 9.37 times that in the absence of glucose, presenting an exciting result on glucose-sensitive self-regulated insulin permeation.

Size-Selective Synthesis of CdS Nanoparticles on Polyethylene Films

Abstract Size-selective CdS nanoparticles were synthesized on polyethylene (PE) films with surface-grafted poly(acrylic acid) (PAAc) chains by the stepwise immersion of the films into aqueous solutions of cadmium acetate and sodium sulfide. By varying the surface density of the PAAc chains, the soaking time, and the number of cycles, it was possible to control the degree of coverage of the film and the size of the CdS nanoparticles.

A comparison of the swelling behaviour of copolymer and interpenetrating network microgel particles

A comparison of the swelling behaviour of two types of hydrogel particles, namely, random poly[(acrylic acid)-co-(acrylamide)] [P(AAc-co-AAm)] particles and PAAc/PAAm interpenetrating network (IPN) particles, has been made using temperature and pH as the triggers. Both types of particles were synthesised by inverse microemulsion polymerisation. The conversion yield of AAc was found to be around 60 wt% due to the partition of this monomer between the aqueous and organic phases. The AAc content was thus lower in the final particles than in the initial composition. Both types of hydrogel particle exhibit an upper critical solution temperature associated with the breakage of the polymer–polymer hydrogen bonds. The maximum swelling ratio occurred in both cases at approximately equimolar AAc and AAm content of the particles. A sharper swelling transition was observed for the PAAc/PAAm IPN particles. This is because of the co-operative nature of the interactions between the PAAc and PAAm chains, the so-called “zipper effect”. A very much higher swelling ratio was obtained using pH as the trigger compared to using temperature. This difference in behaviour is related to the relative strengths of the forces involved in the particle swelling. Electrostatic repulsion forces, associated with the AAc dissociation with increasing pH, are much stronger than the hydrogen bonds.

Apatite coating on hydrophilic polymer-grafted poly(ethylene) films using an alternate soaking process

Previously, we developed a novel alternate soaking process and clarified that bone-like apatite was formed on/in organic polymer hydrogel matrices using this process. The present study focused on the apatite coating on hydrophilic polymer grafted poly(ethylene) (PE) films with various grafting densities and commonly used hydrophilic polymers, poly(acryl amide) (PAAm) and poly(acrylic acid) (PAAc) were employed. From X-ray diffraction analysis, hydroxyapatite was coated on PAAm- or PAAc- grafted PE films. The amount of apatite coated on PAAm-grafted PE (PAAm-g-PE) films increased with an increase in the reaction cycles and the grafting density of PAAm. Similar to PAAm-g-PE, the amount of apatite coated on PAAc-grafted PE (PAAc-g-PE) films increased linearly with an increase in the grafting density of the PAAc up to around 30 μg/cm 2. While, no significant increase in the apatite coating on the PAAc-g-PE films was observed even after 50 reaction cycles when the grafting densities of PAAc were over 30 μg/cm 2. Apatite coating was not observed on original PE films. Scanning electron microscopic images reveal that the aggregation of apatite crystals on all PAAm-g-PE films and PAAc-g-PE films with grafting density from 10 to 30 μg/cm 2. On the other hand, a dense apatite layer with some cracks was coated when the grafting density of the PAAc chains was over 30 μg/cm 2. These results indicated that it was possible to coat apatite on hydrophilic polymer grafted PE films by an alternate soaking process and that the apatite crystal morphology could be controlled as a function of polymer type and density.

Pervaporation of water/isopropanol mixtures through polyaniline membranes doped with poly(acrylic acid)

Polyaniline (PANi) was synthesized by oxidative polymerization and doped with poly(acrylic acid) (PAAc) for pervaporation of aqueous isopropanol. PANi membranes were prepared by solution blending with N-methyl pyrrolidone (NMP) and exhibited the high oxidation stability enough to adopt as dehydration membranes. The conformational hindrance and bulkiness of PAAc chains caused PANi membranes disordered structures. The d-spacings of PANi/PAAc indicated a strong interaction between these two polymers by complexation. When the content of PAAc in doped membrane was 20 wt%, water concentration in permeate decreased to 97 wt%, while permeate flux increased to ca. 200 g/m 2 h due to the affinity of PAAc toward water. Water flux of PANi/PAAc membrane increased with PAAc mixing ratio of up to 30 wt%. Membranes containing more than 30 wt% PAAc showed the analogous results that flux and water concentration in permeate were about 300 g/m 2 h and ∼100 wt%, respectively. Permeate flux through PANi/PAAc membrane decreased with increasing feed IPA concentration while water concentration in permeate was maintained to be over 85 wt%. Water concentration in permeate was much higher than IPA concentration because of high affinity of PANi complex membrane toward water molecules. The activation energy for permeation from an Arrhenius-type expression was ca. 50 KJ/mol.

Atomic Force Microscopic Analysis of a Porous Membrane with pH-Sensitive Molecular Valves

Much attention has been directed to the development of sophisticated membranes that can regulate the permeability in response to environmental changes. In this study, pH-sensitive membranes were prepared by grafting of poly(acrylic acid) (PAAc) onto a porous Nuclepore membrane. The filtration rate of a membrane with a PAAc graft density of 0.30 μg/cm2 was 28 times higher at pH 2.4 than at pH 5.4. Atomic force microscopy (AFM) was employed to make clear how the PAAc graft chains regulate the filtration rate. The thickness of PAAc graft layers was determined from the force curve in buffered solutions of various pHs. It was found that the graft layer thickness was several tens of nanometers at pH 2.6 and increased to 20−430 nm at pH 7.6, depending on the PAAc graft density. The PAAc chains grafted on the membrane surface dynamically changed their configuration in response to the medium pH. In addition, AFM images demonstrated that the graft chains shrank and precipitated on the surface of the membrane and the wall of pores at acidic pHs, thereby opening the pores of the membrane, whereas they hydrated and thus effectively closed the pores at neutral and alkaline pHs. The hydrodynamic permeation in conjunction with AFM observation of the graft layers allowed us to conclude that the PAAc graft chains dynamically opened and closed the pores in response to the medium pH, functioning as a molecular valve to regulate the permeation characteristics.

Synthesis and swelling characteristics of pH and thermoresponsive interpenetrating polymer network hydrogel composed of poly(vinyl alcohol) and poly(acrylic acid)

The swelling behavior of novel pH- and temperature-sensitive interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) in water was investigated. The PVA/PAAc IPN hydrogels were synthesized by UV irradiation, followed by a repetitive freezing and thawing process by which PVA hydrogel networks were formed inside of cross-linked PAAc chains. The swelling behaviors of these IPNs were analyzed in buffer solution at various pH and temperature ranges. Swelling ratios of all IPNs were relatively high, and they showed reasonable sensitivity to both pH and temperature. Hydrogels showed both the positive and negative swelling behaviors depending on PAAc content. IPN46 showed the positive temperature-sensitive swelling behaviors and its stepwise changes in swelling ratio was about 1.8 and 2.0 obtained between 25 and 45°C at pH 7, and between pH 4 and 7 at 35°C, respectively. The positive temperature dependence is attributed to the formation and dissociation of hydrogen bonding complexes between PVA and PAAc. These IPNs are expected to show a pH- and temperature-sensitive drug release according to the stepwise behavior at this temperature region. © 1996 John Wiley & Sons, Inc.