Synthesis and pH-sensitive micellization of doubly hydrophilic poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) triblock copolymer in aqueous solutions

A doubly hydrophilic triblock copolymer poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with M _w/M _n = 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and zeta potential. The pK _a was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH < 5.5 due to hydrogen bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH < 4.5, steady and narrow distributed micelles were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH > 5.5, the micelle was destroyed owing to the ionization of the PAA blocks.     

Polyampholyte gels of a cross-linked polyanion or polycation network into which an oppositely charged polyion was immobilized

Three polyampholyte gels (G1 to G3) composed of acrylic acid (AA), 1-vinylimidazole (VI) and N-isopropylacrylamide (NIPA) were prepared: G1 with a pre-gel solution (pH?≈?12) containing NIPA (700 mM), AA (150 mM), VI (150 mM) and N,N′-methylenebis(acrylamide) (10 mM); G2 with the same pre-gel, except for containing poly(acrylic acid) (PAA) (150 unit mM) instead of AA; and G3 with the same pre-gel, except for containing poly(1-vinylimidazole) (PVI) (150 unit mM) instead of VI. The immobilization of PAA ( $ {\overline M_{\text{w}}} = {2}0{5},000 $ ) and PVI ( $$ {\overline M_{\text{w}}} = <$> <$>35,900 $$ ) resulted in transparent G2 and G3, respectively, while G3 with another PVI ( $ {\overline M_{\text{w}}} = {193},000 $ ) was opaque. Potentiometric titrations and swelling measurements of an anionic and a cationic copolymer gel (as a control sample) suggested that each polyampholyte gel exhibits an isoelectric point (pI) at pH?≈?5.6, at which the electrostatic attraction between the carboxylate and imidazole ions leads to gel collapse. Indeed, all the ampholyte gels underwent a collapse transition at pH around the pI upon cyclic pH changes (first increased and then decreased). The pH region where gel collapse was observed, however, was broader for G2 and G3 (with immobilized polyions) than for G1 (random terpolymer gel). The swelling/deswelling characteristics of transparent and opaque G3 gels were different from each other, and also from those of G1 and G2. These results were discussed in terms of the role of hydrogen bonding of the amide with the carboxyl or imidazole groups in the collapse transition of the ampholyte gels.     

Structural observation of heterogeneous poly(N-isopropyl acrylamide-co-acrylic acid) hydrogels in highly hydrated states

Heterogeneous hydrogels were prepared by -ray irradiation of aqueous solutions of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) having various compositions above the lower critical solution temperature. The structures of the poly(N-isopropylacrylamide) (PNIPAAm) gel and poly(NIPAAm-co-AAc) gels in both their highly hydrated and their natural states were observed by environmental scanning electron microscopy. The heterogeneous structures of the homopolymer gel and the copolymer gels whose AAc contents were between 10–50% consisted of interconnected microspheres. In the copolymer gel with a high AAc content, the structure became a largely interconnected one which lacked micro-droplets. The hydrophobic interaction caused by hydrogen bonding between the unionized carboxylic acid groups of AAc and the amide groups of NIPAAm, the rates of polymerization, and the aggregation rates play important roles in the formation of interconnected microsphere gel structures.     

Swelling of hydrophobically modified poly(acrylamide) and poly(acrylamide)-co-(acrylic acid) gels in surfactant solutions

A series of hydrophobically modified polyacrylamide and polyacrylamide-co-poly(acrylic acid) gels with systematically varying hydrophobicity were prepared by free-radical polymerization of acrylamide, n-alkylacrylamides (n = 10, 12, and 14), and acrylic acid. The swelling of these gels was examined in water and in both anionic and cationic surfactant solutions. It was found that the gels which incorporated acrylic acid showed extremely high swelling in water. Maximum swelling was observed in gels which incorporated 10 mol% acrylic acid. The swelling of these gels was much less in solutions of both anionic and cationic surfactants than in water. The gels which did not incorporate acrylic acid demonstrated little swelling in water, but showed increased swelling in both anionic and cationic surfactant solutions with increased hydrophobicity of the gel. Received: 1 February 1999 Accepted in revised form: 5 March 1999     

Formation of polymer–colloid complexes of aluminoxane particles with poly(acrylic acid) and its copolymers with acrylamide

Formation of polymer–colloid complexes formed by positively charged aluminoxane particles with a size of ~4.6 nm, which constitute the main part of the dispersed phase in aluminum polyhydroxychloride sols with poly(acrylic acid) and acrylic acid copolymers with acrylamide, is studied. Conditions of preparing water-soluble polymer–colloid complexes are determined. It is shown that water-soluble polycomplexes are obtained through the interaction of aluminoxane particles with acrylic acid–acrylamide copolymers containing no more than 0.8 mol% acrylic acid units. In the polymer–colloid complex, aluminoxane particles are uniformly distributed over polyelectrolyte macromolecules and the optimum composition is attained at the molar ratio of components Z equal to 1:1. In semidilute solutions, the addition of aluminoxane particles to the copolymer brings about formation of the gel featuring viscoelastic properties. For all copolymers, the maximally elastic properties of the gels are attained at Z ≈ 1.     

Osmotic deswelling of weakly charged poly(acrylic acid) solutions and gels

The osmotic pressure of weakly charged aqueous poly(acrylic acid) (PAA) solutions and the swelling pressure PAA gels were studied by osmotic deswelling at different degrees of ionization (α). In solution, the osmotic pressure was found to scale linearly with concentration, whereas the scaling power of the swelling pressure of gels was higher (1.66). The effect of the ionization degree on the osmotic coefficient in PAA solutions was in agreement with the theory of Borue and Erukhimovich [Macromolecules, 21 , 3240 (1988)]. Ionization increases the swelling capacity of the PAA gels until a plateau is reached at about 35% neutralization. The concentration at equilibrium swelling scales as C_e ～ α^?0.6. The contribution of the network to the gel swelling pressure is evaluated by subtracting the osmotic pressure of the polymer solution at the same concentration and degree of ionization. In swollen gels the extended network opposes swelling. As the gel is osmotically deswelled, a state of zero network pressure exists at a certain concentration, below which the network elasticity favors swelling. The crossover concentration shifts to lower values as the degrees of ionization increases. © 1995 John Wiley & Sons, Inc.     

Immobilization of Rhodococcus AJ270 and Useof Entrapped Biocatalyst for the Productionof Acrylic Acid

Summary.  Rhodococcus AJ270 is adsorbed by Dowex 1 at 15.4  mg dry weight per g resin with maximum amidase specific activity observed at lower loadings. Bacteria form a monolayer on the resin surface, and adsorption is complete within 2 min. AJ270 can be entrapped in agar and agarose gels (optimum loading: 20 mg dry weight bacteria per cm³ gel). Adsorption and entrapment improve amidase thermal stability 3–4 fold, and entrapment shifts the pH optimum from 8 to 7. Adsorbed and free bacteria show similar values for K _m and V _max, but entrapped bacteria have higher K _m values. Compared with bacteria adsorbed to Dowex, the activity per cm³ of matrix of agar-entrapped AJ270 is eight-fold higher. In stirred-tank reactors, exposure to acrylic acid reduces the amidase activity of the biocatalyst in the hydrolysis of acrylamide. In column reactors, entrapped AJ270 suffers little reduction in amidase activity against 0.25 M acrylamide over 22 h continuous operation. Received November 18, 1999. Accepted December 14, 1999     

Preparation,characterization of cationic terbium luminescent copolymer and its interaction with DNA

A complex of Tb³⁺, acrylic acid (AA), and 1, 10-phenanthroline (Phen) was synthesized. The structure and fluorescence of Tb(AA)₃Phen·H₂O was characterized with elemental analysis, FT-IR, and fluorescence spectroscopy. A novel copolymer containing rare earth complex, poly (METAC-co-NIPAm-co-Tb(AA)₃Phen·H₂O) (PMNTb), was prepared by free radical copolymerization in methanol with azodiisobutyronitrile (AIBN) as initiator. ¹H NMR, fluorescence spectroscopy, UV-vis spectroscopy, and TEM were used to characterize this copolymer. The interaction of PMNTb with DNA was studied by fluorescence spectroscopy, UV-vis spectroscopy, and agarose gel electrophoresis. The results of fluorescence, UV-vis absorption, and agarose electrophoresis indicated that the PMNTb could interact with DNA in an electrostatic bonding mode and the bonding constant was 3.4 × 10⁵ L mol⁻¹. The TEM observation showed that the PMNTb could form micelles in water solution; the efficient complexation of PMNTb with DNA occurred. The results of in vitro cytotoxicity indicated that PMNTb had good biocompability. These results laid the foundation for the further study in potential gene detective reagent and gene delivery carrier.     

Drying dissipative structures of the thermosensitive gels of poly(N-isopropyl acrylamide) on a cover glass

Drying dissipative structural patterns of the thermosensitive gels of poly(N-isopropyl acrylamide) were studied on a cover glass. As the temperature of suspension and room rose from 25 to 50 °C, the small size of drying pattern area extended to the beautiful flickering spoke-like ones transitionally at the critical temperature ca. 35 °C. The principal patterns at 25 °C were the single or multiple broad rings of the hill accumulated with the gels. At 50 °C, on the other hand, the flickering spoke-like patterns were observed at the inner area of the broad ring especially at the gel concentrations higher than 1 × 10⁻³ g/ml. These observations support that the extended gels at low temperatures apt to associate weakly to each other, whereas the gels at high temperatures shrink and move rather freely with the convectional flow of water, though the very weak intergel attractions still remain. In the presence of sodium chloride at high temperatures, the cooperative patterns formed between the gel spheres and the salt. The gravitational and Marangoni convectional flow of the gels and the very weak interactions between the gels and substrate (cover glass) are important for the flickering spoke-like pattern formation.     

A sensitive semi-micro column HPLC method with peroxyoxalate chemiluminescence detection and column switching for determination of MDMA-related compounds in hair

A sensitive semi-micro column HPLC method with peroxyoxalate chemiluminescence (POCL) detection and column switching has been developed for simultaneous determination of 3,4-methylenedioxymethamphetamine (MDMA) and related compounds, for example 3,4-methylenedioxyamphetamine, methamphetamine, and amphetamine, in hair. After digestion of the hair with 1 mol L⁻¹ sodium hydroxide the compounds were extracted with n-heptane and derivatized with 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole. A mixture of hydrogen peroxide and bis(2,4,5-trichloro-6-carbopentoxyphenyl)oxalate in acetonitrile was used as post-column CL reagent. Calibration plots showed linearity was good (r = 0.999); detection limits were 0.02–0.16 ng mg⁻¹ hair at a signal-to-noise ratio of 3. The precision of the method, as RSD (n = 5), in intra-day and inter-day assays was better than 5.0 and 6.9%, respectively. The proposed method was sufficiently sensitive to detect low ng mg⁻¹ levels of MDMA and related compounds in hair, and could be used for quantification of the compounds in hair samples from patients treated in a chemical dependency unit.     

Electrooxidation of undiluted organic liquids swelling<Emphasis Type="Italic"> N</Emphasis>-isopropylacrylamide-based copolymers

Polyacrylate gels such as: N-isopropylacrylamide (NIPA), ionic copolymer NIPA-co-sodium acrylate (NIPA-co-SA) and ionic copolymer NIPA-co-[2-(acryloyloxy)ethyl]trimethylammonium chloride (NIPA-co-XCl) were swollen by methanol, ethanol and N,N-dimethylformamide. These solvents were oxidized voltammetrically in the gels at platinum microelectrodes. The blocking coefficients, defined as the ratio of the currents observed in the presence and absence of the polymeric chains, were different for the solvents in the charged and uncharged polymers and did not differ for the electroactive probe, ferrocene, present in the solvents at millimolar level. This may mean that the micro ionic layer that is formed at microelectrodes at the plateau of the voltammetric solvent waves leads to a kind of collapse/phase transition of the polymer in the depletion layer. For methanol, the gel structure was found to prevent occasionally the formation of large gas bubbles at the potentials positive versus the first wave and then three one-electron waves could be obtained. Experiments done with a capillary cell and an optical microscope indicated that before formation of large bubbles at the Pt microelectrode a very dynamic, dense stream of microbubbles leaves the electrode surface.Dedicated to Zbigniew Galus on the occasion of his 70th birthday     

A novel reversible pH-triggered release immobilized enzyme system

A novel immobilized enzyme system supported by poly(acrylic acid/N,N’-methylene-bisacryl-amide) hydrogel microspheres was prepared. This system exhibited characteristics of reversible pH-triggered release. The morphology, size, and chemical structure were examined through optical microscopy, particle size analyzer, and Fourier transform infrared spectrometer. Immobilization and release features were further investigated under different conditions, including pH, time, and microsphere quantity. Results showed the microspheres were regularly spherical with 3.8 ~ 6.6 μm diameter. Loading efficiencies of bovine serum albumin immobilized by gel entrapment and adsorption methods were 93.9% and 56.2%, respectively. The pH-triggered protein release of the system occurred when medium pH was above 6.0, while it was hardly detected when medium pH was below 6.0. Release efficiencies of entrapped and adsorbed protein were 6.38% and 95.0%, respectively. Hence, adsorption method was used to immobilize trypsin. Loading efficiency of 77.2% was achieved at pH 4.0 in 1 h. Release efficiency of 91.6% was obtained under optimum pH catalysis condition set at 8.0 and trypsin was free in solutions with retention activity of 63.3%. And 51.5% of released trypsin could be reloaded in 10 min. The results indicate this kind of immobilized enzyme system offers a promising alternative for enzyme recovery in biotechnology.     

pH/temperature dual stimuli-responsive microcapsules with interpenetrating polymer network structure

The microcapsules with interpenetrating polymer network (IPN) structure based on crosslinked poly (N-isopropylacrylamide) (PNIPAM) and crosslinked poly (acrylic acid) (PAA) were fabricated in a three-step process. Firstly, silica/PNIPAM core/shell composite particles were synthesized by thermo-initiated seed precipitation polymerization using 3-(trimethoxysilyl)propyl methacrylate modified silica colloidal particles as seeds and N-isopropylacrylamide and N,N′-methylenebisacrylamide (MBA) as monomer and crosslinker, respectively. Secondly, PAA network was incorporated into the shell of the composite particles by redox-initiated polymerization of acrylic acid and MBA entrapped in the PNIPAM network. Finally, the silica core of the composite particles was removed using hydrofluoric acid under certain condition to produce the microcapsules. The chemical compositions, their mass ratio, and particle sizes of the particles formed in each step were determined by Fourier transformation infrared spectroscopy, thermogravimetry, and dynamic laser light scattering (DLLS), respectively. The IPN structure of the microcapsules was identified by transmission electron microscopy (TEM) using uranyl acetate staining method, and their hollow structure was evidenced by TEM and scanning electron microscopy. Their temperature- or pH-dependent hydrodynamic diameters were measured by DLLS, and the results showed that the microcapules had both pH- and temperature-responsive properties, and the temperature-responsive component and the pH-responsive component inside the microcapsule shell had little interference with each other.     

Electrochemical behaviors of metol on ionic-liquid-modified carbon paste electrode and its analytical application

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k _s) as 4.02 × 10⁻³ s⁻¹, and the diffusion coefficient (D) as 6.35 × 10⁻⁵ cm²/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10⁻⁶ ∼ 1.0 × 10⁻³ mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10⁻⁶ mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.     

Polyelectrolyte complexes of linear copolymers and hydrogels based on 2‐[(methacryloyloxy)ethyl]trimethylammonium chloride and N‐isopropylacrylamide

The formation of polyelectrolyte complexes of linear copolymers and hydrogels based on copolymers of 2‐[(methacryloyloxy)ethyl]trimethylammonium chloride with N‐isopropylacrylamide (MADQUAT–NIPAAM) and poly(acrylic acid) (PAA) has been studied. The composition of the copolymer has been found to affect the composition of the polyelectrolyte complexes significantly, and the molecular weight of PAA influences their aggregation stability. Hydrogels of MADQUAT–NIPAAM immersed in solutions of PAA undergo contraction because of the formation of gel–polymer complexes. The rate of contraction and the final swelling degree of the gel–polymer complexes depend on the concentration of PAA in solution and its molecular weight. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1506–1513, 2004     

The incorporation of carboxylate groups into temperature‐responsive poly(N‐isopropylacrylamide)‐based hydrogels promotes rapid gel shrinking

Aqueous gel deswelling rates for copolymer hydrogels comprising N‐isopropylacrylamide (IPAAm) and 2‐carboxyisopropylacrylamide (CIPAAm) in response to increasing temperatures were investigated. Compared with pure IPAAm‐based gels, IPAAm–CIPAAm gels shrink very rapidly in response to small temperature increases across their lower critical solution temperature (their volume is reduced by five‐sixths within 60 s). Shrinking rates for these hydrogels increase with increasing CIPAAm content. In contrast, structurally analogous IPAAm–acrylic acid (AAc) copolymer gels lose their temperature sensitivity with the introduction of only a few mole percent of AAc. Additionally, deswelling rates of IPAAm–AAc gels decrease with increasing AAc content. These results indicate that IPAAm–CIPAAm copolymer gels behave distinctly from IPAAm–AAc systems even if both comonomers, CIPAAm and AAc, possess carboxylic acid groups. Thus, we propose that the sensitive deswelling behavior for IPAAm–CIPAAm gels results from strong hydrophobic chain aggregation maintained between network polymer chains due to the similar chemical structures of CIPAAm and IPAAm. This structural homology facilitates aggregation of chain isopropylamide groups for both IPAAm and CIPAAm sequences with increasing temperature. The incorporation of AAc, however, shows no structural homology to IPAAm, inhibiting chain aggregation and limiting collapse. A functionalized temperature‐sensitive poly(N‐isopropylacrylamide) hydrogel containing carboxylic acid groups is possible with CIPAAm, producing rapid and large volume changes in response to smaller temperature changes. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 335–342, 2001     

Fast responsive poly(<Emphasis Type="Italic">N,N</Emphasis>-diethylacrylamide) hydrogels with interconnected microspheres and bi-continuous structures

We prepared thermo-responsive polymer hydrogels by γ-ray irradiation of aqueous solutions of N, N-diethylacrylamide at different temperatures below and above its lower critical solution temperature (LCST). Poly(N, N-diethylacrylamide) gel had a transparent and homogeneous structure when the radiation-induced polymerization and crosslinking were carried out below the LCST (25 °C) of the polymer. On the other hand, cloudy and heterogeneous gels were formed at temperatures above the LCST of the polymer (>35 °C). From environmental scanning electron microscopy observations, the gels prepared at 35 and 40 °C were seen to show sponge-like bi-continuous porous structures, while those prepared at 50 °C showed a porous structure consisting of interconnected microspheres. For temperature changes between 10 and 40 °C, gels with porous structures showed rapid volume transitions on a time scale of about a minute, not only for shrinking but also for swelling processes, which is in remarkable contrast to the porous poly(N-isopropylacrylamide) hydrogels.     

Swelling–shrinking behaviors of poly(N-isopropylacrylamide) and poly(N-n-propylacrylamide) gels prepared by chemical and radiation crosslinking methods

The swelling and shrinking kinetics of thermosensitive gels based on N-isopropylacrylamide (NiPAAm) and N-n-propylacrylamide (NnPAAm) were studied. Four gels cylindrical in shape were prepared by two different methods: γ-ray irradiation to aqueous solutions of poly(NiPAAm) (PNiPAAm) or poly(NnPAAm) (PNnPAAm) and redox polymerization of NiPAAm or NnPAAm monomer using N,N′-methylenebisacrylamide as a crosslinker. There were a few differences in the swelling kinetics among these gels. However, a marked difference was observed in the shrinking processes, the rate of which was faster in the order of radiation-crosslinked PNiPAAm gel > radiation-crosslinked PNnPAAm gel > chemically crosslinked PNnPAAm gel > chemically crosslinked PNiPAAm gel. This difference was discussed in terms of the microscopic structure of the gels, which was studied by light scattering techniques. It was found that the static inhomogeneities frozen in the chemically and radiation-crosslinked gels play a key role in their shrinking kinetics.     

Investigation of the effect of type and concentration of ionizable comonomer on the collapse behavior of N-isopropylacrylamide copolymer gels in water

This work was done to investigate the effect of three different ionizable components (acrylic acid, AA; itaconic acid, IA; maleic acid, MA) on the volume phase transitions and swelling equilibria of thermoshrinking type N-isopropylacrylamide (NIPAAM) gels in water. NIPAAM copolymer gels were synthesized by free radical crosslinking copolymerization of NIPAAM with each of AA, IA, and MA, the difference being both between configurations and carboxyl group numbers, and pK values, in the presence of N,N′-methylene-bis-acrylamide (MBAAM). The influence of comonomer concentrations (1, 5, and 10 mol %), MBAAM content (0.0096, 0.0193, and 0.0288 g), and comonomer type (AA, IA, and MA) on the external views, the percentages of equilibrium mass, and volume swellings [S %(m), S % (v)], the number-average molecular weight between crosslinks (M̄_c), effective crosslinking densities (ν_e), the change of the collapse temperatures, and swelling ratios in the swelling–shrinking process of the gels were examined. It was observed that phase transition temperature and swelling degree in the case of MA having a cis configuration and higher pK value are larger than those of the samples containing IA and AA. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1847–1855, 1999     

Antimicrobial loading into and release from poly(ethylene glycol)/poly(acrylic acid) semi‐interpenetrating hydrogels

Electrostatic interactions within a semi‐interpenetrating network (semi‐IPN) gel can control the postsynthesis loading, long‐term retention, and subsequent release of small‐molecule cationic antibiotics. Here, electrostatic charge is introduced into an otherwise neutral gel [poly(ethylene glycol) (PEG)] by physically entrapping high‐molecular‐weight poly(acrylic acid) (PAA). The network structure is characterized by small‐angle neutron scattering. PEG/PAA semi‐IPN gels absorb over 40 times more antibiotic than PAA‐free PEG gels. Subsequent soaking in physiological buffer (pH 7.4; 0.15 M NaCl) releases the loaded antibiotics for periods as long as 30 days. The loaded gels elute antibiotics with diffusivities of 4.46 × 10^?8 cm²/s (amikacin) and 2.08 × 10^?8 cm²/s (colistin), which are two orders of magnitude less than those in pure PEG gels where diffusion is controlled purely by gel tortuosity. The release and hindered diffusion can be understood based on the partial shielding of the charged groups within the loaded gel, and they have a significant effect on the antimicrobial properties of these gels. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 64–72