Swelling behavior of chitosan/poly(acrylic acid) complex

This study investigates the improved swelling behavior of chitosan/poly(acrylic acid) complex by solvent (methanol, ethanol, and acetone) extraction. The complex is developed by photoinitiated free‐radical polymerization of acrylic acid in the presence of chitosan. The swelling ratio of the complexes depends on the cosolvency effect of poly(acrylic acid) to the extracted solvent, which in turn affects the polymer network structure and ionic states characterized by dynamic force microscopy (DFM), Raman, and FT‐IR spectroscopy. The DFM investigation displays the improved structural changes of the polymer network structure after solvent extraction and its relation to the improved swelling property of the chosen system in different environmental conditions (pH, solvent, and salt concentration) are discussed. A high swelling ratio of about 600 times its dry weight is observed in water as well as in low salt and solvent concentration after methanol extraction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2930–2940, 2004     

Characterization of polyelectrolyte effect in poly(acrylic acid) solutions

The viscometric behavior of poly(acrylic acid) solutions, as well as their ion transport properties, were monitored as a function of polymer concentration and the addition of KOH in nonisoionic conditions. Polyelectrolyte effect was studied and characterized by conductivimetry as well as viscometric properties at the infinite dilution limit. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 191–196, 2003     

Structure and properties of the polyelectrolyte complex of chitosan with poly(methacrylic acid)

The structure and properties of the polyelectrolyte complex composed of chitosan (CS) and poly(methacrylic acid) (PMAA) were studied in aqueous solutions using UV‐visible transmittance measurements, a fluorescence probe technique, and transmission electron microscopy. The thermal properties of the solid complex were measured using differential scanning calorimetry. The results showed that the complex optimum molar ratio (in monomer unit) of CS to PMAA is 1:4 at pH = 4.0, that is, there is an optimum complex between CS and PMAA when the feed ratio (in molar monomer unit) of CS to PMAA is 1:4 and an ionic bond between the amino ion group and carboxylate group can be formed on average every four carboxylate (or carboxyl) groups. The conformation of PMAA changed from a hypercoiled to a loose coil on complexation, and the pH‐ and salt‐sensitive range of the polyelectrolyte complex was obviously different from that of CS or PMAA. The formation process of the complex under various external conditions is discussed in detail. Transmission electron microscopy revealed that the sizes of CS–PMAA complex particles increased with increasing pH or salt concentration, and a change in morphology of the complex was observed. Thermal analysis further revealed that there was a change of structure and properties on blending in aqueous solutions. Copyright © 2007 Society of Chemical Industry     

Comparison of poly(aspartic acid) hydrogel and poly(aspartic acid)/gelatin complex for entrapment and pH‐sensitive release of protein drugs

Biodegradable poly(aspartic acid) (PASP) hydrogel and PASP/gelatin complex were prepared to evaluate their potential application as pH‐sensitive matrices for controlled protein release. Entrapment of myoglobin (Mb) and its release were compared between the two types of carriers. It was found that incorporation of Mb into PASP hydrogel strongly depended on the medium pH and NaCl concentration, and was time‐consuming. However, complete entrapment of Mb into PASP/gelatin complex was found within pH ranged from 2.5 to 4.0, which was concomitant with the formation of PASP/gelatin complex. By adjusting Mb feed ratio, Mb entrapment in the complex can be up to 31.54% (by weight) with high loading efficiency (96.2%). Gradual release of Mb from PASP hydrogel was observed within pH 2.0–7.4, while Mb release from PASP/gelatin complex was negligible within pH 2.0–4.2 for 4 days. In addition, pulsatile Mb release can be achieved by combining polyanhydride with pH‐sensitive PASP/gelatin complex, while the device composed of polyanhydride and PASP hydrogel is mechanically unstable. PASP/gelatin complex formed by electrostatic interactions is superior to the single‐component PASP hydrogel synthesized by chemical cross‐linking as pH‐sensitive matrices for controlled protein release when entrapment of proteins and pH‐sensitivity of protein release are concerned. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Polyelectrolyte complexes based on chitosan and poly(L‐glutamic acid)

Polyelectrolyte complexes (PECs) were prepared by mixing aqueous solutions of chitosan (CS) and poly(L ‐glutamic acid) (PLGA) at various pH. It was found that the stoichiometry of the PECs depends on pH. An investigation of the PECs using Fourier transform infrared spectroscopy proved that the formation of the complexes is due to electrostatic interaction between ? NH₃⁺ groups of CS and ? COO^? groups of PLGA. The solid PECs were characterized using wide‐angle X‐ray diffraction, which suggested that a strong interaction occurs between the two polymers at pH = 4 or 5 and relatively weak interaction at pH = 3. These results were further confirmed by thermogravimetric analysis data. Transmission electron microscopy showed that the complexes have a spherical shape. The effect of ionic strength on the size of the PECs was also studied using dynamic light scattering. It was found that the size of the PECs is dependent on pH. Copyright © 2007 Society of Chemical Industry     

Synthesis and stimuli-responsive properties of chitosan/poly(acrylic acid) hollow nanospheres

We report here a synthetic study on the formation process of hollow polymeric nanospheres based on a simple, core-template-free route, and the effects of polymerization concentration, shell cross-linking, pH, salt concentration and temperature on the size and stability of hollow polymeric nanospheres. The hollow structure of polymeric nanospheres is spontaneously formed by polymerization of acrylic acid monomers inside the chitosan–acrylic acid assemblies. It is found that (i) the hollow structure of nanospheres is stabilized by both physical cross-linking in the inner shell and chemical cross-linking in the outmost shell; (ii) the size of the hollow spheres can be adjusted over the range of 77–500 nm by controlling the concentration of chitosan–acrylic acid assemblies in the reaction system; (iii) the synthesized nanospheres are stimuli-responsive. The size of the hollow nanospheres can be manipulated by changing pH, salt concentration and temperature. Furthermore, with heating and cooling the variation in size of hollow nanospheres is completely reversible and reproducible; (iv) the surface of the hollow nanospheres obtained is chemically active, which provides the functional sites with chemical groups for subsequent chemical reactions at the surface.     

Effect of hydrophobic units on the pH‐responsive release property of polyelectrolyte complex capsules

Copolymers of acrylic acid and styrene with styrene unit contents of 2.7, 5.7, and 9.5% were synthesized by free radical copolymerization. Poly(ethylenimine)s with benzylated unit contents of 2.4, 6.0, 10.6, and 16.7% were obtained by the reaction of poly(ethylenimine) with benzyl bromide. Polyelectrolyte complex capsules consisting of these polymers were prepared. Influence of the hydrophobic units on pH‐responsive release property of the capsules was studied using phenylethylene glycol as a permeant. When the copolymer with styrene unit content of 5.7% or the poly(ethylenimine) with the benzylated unit content of 2.4–10.6% was used as the membrane components, the permeability of the capsule membrane became minimum and was 10–20 fold lower than that of the poly(acrylic acid)–poly(ethylenimine) complex capsule membrane in the pH region between 3 and 7. In contrast, the hydrophobic units did not lower the permeability of the capsule membranes significantly below pH 3 and above pH 7. Thus, the capsule membranes containing hydrophobic units exhibited remarkable permeability changes in the narrow pH regions of 2–3 and 7–9. Also, the capsule containing the benzylated PEI in the membrane changed the release rate of the contents very quickly, in response to the ambient pH alteration. Therefore, polyelectrolyte complex capsules, which are highly sensitive to pH change, were obtained by using the polyelectrolytes with the hydrophobic units as membrane components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1763–1773, 1999     

Synthesis of poly(N,N‐diethylacrylamide‐co‐acrylic acid) hydrogels with fast response rate in NaCl medium

A series of thermo‐ and pH‐sensitive poly (N,N‐diethylacrylamide‐co‐acrylic acid) (P(DEA‐co‐AA)) hydrogels were prepared in NaCl aqueous solutions with different concentrations. Swelling and deswelling studies showed that in comparison with conventional P(DEA‐co‐AA) hydrogels (prepared in distilled water), the P(DEA‐co‐AA) hydrogels thus prepared had almost the same volume phase transition temperature (VPTT), but exhibited much faster response rates as the temperature was raised above their VPTT. Besides, the hydrogels prepared by this method had faster response rates in low pH buffer solutions, and the response rates increased with the increased concentration of the NaCl solutions used during the polymerization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Studies on chitosan and poly(acrylic acid) interpolymer complex. I. Preparation,structure, pH-sensitivity,and salt sensitivity of complex-forming poly(acrylic acid): Chitosan semi-interpenetrating polymer network

A novel semi-interpenetrating polymer network (semi-IPN) membrane composed of crosslinked chitosan(cr-CS) and poly(acrylic acid) (PAA) was prepared. Evidence from infrared spectra proved the formation of polyelectrolyte complex through electrostatic interaction between groups from CS and COO⁻ groups from PAA. The semi-IPN membrane swelled at high pH and at low pH exhibited a typical pH-sensitivity. Its swelling degrees in different salt solutions with the same ionic valence and equal ionic strength were on similar levels. Under certain ionic strength (I = 1.5 mol/L), the degree of swelling increased with increased metal ionic valence. Furthermore, the elongation of the semi-IPN membrane could vary reversibly by immersion into CaCl₂ solution and KCl solution alternately. Reasons for the chemomechanical behavior are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1445–1450, 1997     

Ultra-fine polyelectrolyte fibers from electrospinning of poly(acrylic acid)

Ultra-fine polyelectrolyte fibers have been generated from electrospinning of poly(acrylic acid) in aqueous and DMF solutions. The fiber diameters ranged from 80 to 500 nm and increased with increasing solution concentrations and electrospinning voltages. The fibers generated from the aqueous solutions were more homogeneous in sizes, especially when NaCl or NaOH was added. Higher voltages in electrospinning of the aqueous solutions also resulted in fibers with larger heat capacity in the glass transition region, and higher dehydration temperatures. These polyelectrolyte fibers could be rendered water-insoluble by incorporating β-cyclodextrin (at 20 wt% of PAA) in the aqueous solution, then heat-induced crosslinking was performed at 140 °C for 20 min. The resulting hydrogel fibers showed strongly pH-responsive swelling behaviors.     

壳聚糖/聚丙烯酸共聚物微球的制备及性能

以环己烷为油相,壳聚糖溶液为水相,运用反相乳液聚合法制得了具有pH敏感性的壳聚糖/聚丙烯酸共聚物微球。讨论了微球在pH=1～10缓冲溶液中的溶胀率变化,研究表明,微球在强酸性(pH≈1)和碱性(pH>7)条件下,溶胀率均在10倍以上;而在pH=2～6时溶胀较差,当pH=4时出现最低值,溶胀率低于1倍。光学显微镜所观察到的微球粒径均在40μm以内,且大小均匀。采用傅里叶红外光谱仪分析了不同配比样品特征峰的峰值和峰面积的变化。用722光栅分光光度计研究了共聚物微球包埋考马斯亮蓝的溶胀释放过程。     

Thermal behavior of poly(acrylic acid)–poly(vinyl pyrrolidone) and poly(acrylic acid)–metal–poly(vinyl pyrrolidone) complexes

Thermal analysis (TGA and DTA) of samples of PAA, PVP, PAA–PVP complexes, containing different weight fractions of PAA and ternary polymer–metal–polymer complexes, were studied. The activation energy parameters for the thermal degradation were also calculated. The study of the effect of FeCl₃, NiCl₂, and Ni(NO₃)₂ on the TGA and DTA curves of the complexes showed that the decompositions are dependent on the concentrations and the nature of the metal ions. The DTA traces of PAA–PVP complex containing FeCl₃, NiCl₂, and Ni(NO₃)₂ showed that the treatment of the complex with these metal ions causes considerable changes in the thermal decomposition of PAA–PVP complex. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4049–4057, 2006     

Characterization of strong polyelectrolyte hydrogels based on poly(vinyl alcohol)

Maleic anhydride (MA) was grafted onto both partially and fully hydrolyzed poly(vinyl alcohol) (PVA) in the presence of an initiator. Strong polyelectrolyte polymers were prepared by sulfonation of PVA–MA grafts. The sulfonation was completed by reaction of hydroxyl groups of PVA–MA grafts with two different sulfonating reagents (chlorosulfonic acid and pyridine sulfonic acid). The sulfonation degree was evaluated by acid–base titration and ¹H NMR analysis. The solution behaviour of the prepared grafts was evaluated from viscosity measurements. Four kinds of water‐insoluble PVA–MA and PVA–MA‐SO₃H hydrogels were prepared by heat treatment, physical gelation and chemical crosslinking with different weight ratios of N,N‐methylene bisacrylamide (MBA) crosslinker. The swelling parameters were measured for all prepared gels in deionized water and aqueous solutions at different pH values from 2 to 12 having constant ionic strength (I = 0.1). All gels exhibit a different swelling behaviour upon environmental pH changes. Copyright © 2004 Society of Chemical Industry     

Fabrication and characterization of centrifugally spun poly(acrylic acid) nanofibers

The production of poly(acrylic acid) (PAA) nanofibers by the centrifugal spinning of PAA solutions in water is reported. The effect of the spinneret rotational speed and concentration of PAA solutions on the diameter of nanofibers and on their quality (assessed by the absence of beads) is discussed. The main physical properties of PAA such as glass-transition temperature (T_g) are studied in detail and compared to the feature of the as-received homopolymer. It is shown that the glass-transition temperature of the bulk PAA and PAA nanofibers (as measured by differential scanning calorimetry) depends on the heating rate according to a Williams–Landel–Ferry-like equation. Raman spectroscopy data provided additional information about the differences between the as-received polymer and the nanofibers. Preliminary results on antibacterial properties of the PAA nanofibers are reported. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47480.     

The intrinsic viscosity of poly(acrylic acid) and partially neutralized poly(acrylic acid) by isoionic dilution

The isoionic dilution method has been used to measure the intrinsic viscosity, [η], of a poly(acrylic acid) (PAA) sample as a function of neutralization degree, i, at low ionic strength, I = 1.0 × 10. The results obtained for the counterion activity are in close agreement with Manning's theory for counterion condensation. The influence of the ionic strength, I, on [η] and on the Huggins coefficient, k', was also examined and the exponents of the scaling laws relating these two parameters with I were found.     

A supramolecular structured complex of poly(acrylic acid) and polystyrene‐block‐poly(vinylbenzyltrimethylammonium chloride)

Complexation of poly(acrylic acid) (PAA) by polystyrene‐block‐poly(vinylbenzyltrimethylammonium chloride) (PS‐b‐VB) results in a mesomorphously ordered material with a glass transition temperature of 71 °C. The complex is assumed to consist of hexagonally‐ordered ion‐rich cylindrical rods containing the PAA embedded in a polystyrene matrix. It has been shown by small‐angle X‐ray scattering (SAXS) analysis that the mesophase is characterized by sharp phase boundaries between ionic and non‐ionic regions. The structure parameters are evaluated by using a two‐dimensional interface distribution function resulting in an average cylinder radius in the range 3.0–3.5 nm and a lattice constant of 14 nm. The radius distribution is calculated to be relatively broad, which is found to be consistant with sharp phase boundaries. PS‐b‐VB‐PAA represents an example of a new type of polymeric hybrid material with a supramolecular ordered ionic–non‐ionic nanostructure. © 2000 Society of Chemical Industry     

Synthesis and characteristics of semi‐interpenetrating polymer network hydrogels based on chitosan and poly(hydroxy ethyl methacrylate)

Semi‐interpenetrating polymer networks (semi‐IPNs), composed of chitosan and poly(hydroxy ethyl methacrylate) hydrogels, were prepared and the effects of various pH, temperatures, and an electric‐field on the swollen hydrogels were investigated. The swelling kinetics increased rapidly, reaching equilibrium within 60 min. Semi‐IPN hydrogels exhibited relatively high swelling ratios, 150～350%. The swelling ratio increased when the pH of the buffer was below pH 7 as a result of the dissociation of ionic bonds. Semi‐IPN hydrogels showed electroresponsiveness by shrinking when an electric field was applied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 86–92, 2005     

Glass polyalkenoate dental cements based on physical blends of poly(acrylic acid) and poly(vinyl phosphonic acid)

Physical blends of spray-dried poly(acrylic acid), PAA, with poly(vinyl phosphonic acid), PVPA, have been prepared and used in experimental dental cements by mixing them with basic sub-45 μm acid-degradable fluoroaluminosilicate glass powders and adding water. The effect of varying the ratio of PAA to PVPA, of altering the molar mass of PAA, and of using glasses of differing basicity have been investigated. The compressive strengths of the best of the cements formed from these blends were comparable to those formed from the individual polyacids, i.e. about 160 MPa.     

Synthesis and characterization of fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels

BACKGROUND: A considerable amount of research has been focused on smart hydrogels that can respond to external environmental stimuli, especially temperature and pH. In this study, fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels were prepared by free radical copolymerization in aqueous solution using poly(ethylene glycol) (PEG) as a pore‐forming agent. RESULTS: Swelling studies showed that the hydrogels produced had both temperature and pH sensitivity. The deswelling kinetics at high temperature demonstrated that the shrinking rates were influenced by the addition of the pore‐forming agent and the amount of acrylic acid in the initial total monomers. The deswelling curves in low‐buffer solutions had two stages. Pulsatile swelling studies indicated that the PEG‐modified hydrogels were superior to the normal ones. These different swelling properties were further confirmed by the results of scanning electron microscopy. CONCLUSION: Such fast responsive thermo‐ and pH‐sensitive hydrogels are expected to be useful in biomedical fields for stimuli‐responsive drug delivery systems. Copyright © 2008 Society of Chemical Industry     

Interpolymer complexes of poly(acrylamide) and poly(N-isopropylacrylamide) with poly(acrylic acid): a comparative study

The interpolymer complexation, through successive hydrogen bonding, between poly(acrylamide) (PAAm) and poly(N-isopropylacrylamide) (PNiPAAm) with poly(acrylic acid) (PAA) in aqueous solution has been viscometrically and potentiometrically investigated. The stoichiometry of the complexes formed was determined. By comparing the strength of the two complexes the very important contribution of the hydrophobic interaction in their formation has been indicated.