Synthesis of poly(acrylic acid)–Fe3+/gelatin/poly(vinyl alcohol) triple‐network supramolecular hydrogels with high toughness,high strength and self‐healing properties

Hydrogels with good mechanical and self‐healing properties are of great importance for various applications. Poly(acrylic acid)–Fe³⁺/gelatin/poly(vinyl alcohol) (PAA‐Fe³⁺/Gelatin/PVA) triple‐network supramolecular hydrogels were synthesized by a simple one‐pot method of copolymerization, cooling and freezing/thawing. The PAA‐Fe³⁺/Gelatin/PVA triple‐network hydrogels exhibit superior toughness, strength and recovery capacity compared to single‐ and double‐network hydrogels. The mechanical properties of the synthesized hydrogels could be tailored by adjusting the compositions. The PAA‐Fe³⁺/Gelatin/PVA triple‐network hydrogel with 0.20 mmol Fe³⁺, 3% gelatin and 15% PVA could achieve good mechanical properties, the tensile strength and elongation at break being 239.6 kPa and 12.8 mm mm^?1, respectively, and the compression strength reaching 16.7 MPa under a deformation of about 91.5%. The synthesized PAA‐Fe³⁺/Gelatin/PVA triple‐network hydrogels have good self‐healing properties owing to metal coordination between Fe³⁺ and carboxylic groups, hydrogen bonding between the gelatin chains and hydrogen bonding between the PVA chains. Healed PAA‐Fe³⁺(0.20)/Gelatin3%/PVA15% triple‐network hydrogels sustain a tensile strength of up to 231.4 kPa, which is around 96.6% of the tensile strength of the original samples. Therefore, the synthesized triple‐network supramolecular hydrogels would provide a new strategy for gel research and expand the potential for their application. © 2019 Society of Chemical Industry     

Multiple Shape Memory,Self‐Healable,and Supertough PAA‐GO‐Fe3+ Hydrogel

A multiple shape memory and self‐healing poly(acrylic acid)‐graphene oxide‐Fe³⁺ (PAA‐GO‐Fe³⁺) hydrogel with supertough strength is synthesized containing dual physically cross‐linked PAA network by GO and Fe³⁺. The first GO cross‐linked hydrogel can be reversibly reinforced by immersing in FeCl₃/HCl and pure water and softened by immersing in HCl. The tensile strength is 2.5 MPa with the break strain of 700%. Multiple shape memory capability is found depending on this unique feature, the hydrogel can be fixed in four temporary shapes by adjusting the immersing time in FeCl₃/HCl and pure water, and recovered in sequence by immersing in HCl. This hydrogel also exhibits perfect self‐healing behavior, the cut as‐prepared hydrogel is almost completely healed by immersing in FeCl₃/HCl. Besides, the hydrogel shows enhanced electrical conductivity with the presence of GO and Fe³⁺. This supertough hydrogel provides a new way to design soft actuators.

     

A Dual‐Crosslinked Strategy to Construct Physical Hydrogels with High Strength,Toughness, Good Mechanical Recoverability,and Shape‐Memory Ability

A novel type of physical hydrogel based on dual‐crosslinked strategy is successfully synthesized by micellar copolymerization of stearyl methacrylate, acrylamide, and acrylic acid, and subsequent introduction of Fe³⁺. Strong hydrophobic associations among poly(stearyl methacrylate) blocks form the first crosslinking point and ionic coordination bonds between carboxyl groups and Fe³⁺ serve as the second crosslinking point. The mechanical properties of the hydrogel can be tuned in a wide range by controlling the densities of two crosslinks. The optimal hydrogel shows excellent mechanical properties (tensile strength of ≈6.8 MPa, elastic modulus of ≈8.0 MPa, elongation of ≈1000%, toughness of 53 MJ m^?3) and good self‐recovery property. Furthermore, owing to stimuli responsiveness of physical interaction, this hydrogel also shows a triple shape memory effect. The combination of two different physical interactions in a single network provides a general strategy for designing of high‐strength hydrogels with functionalities.     

Superabsorbent composite. XIII. Effects of Al3+‐attapulgite on hydrogel strength and swelling behaviors of poly(acrylic acid)/Al3+‐attapulgite superabsorbent composites

Al³⁺‐attapulgite (Al³⁺‐APT) was prepared by treating attapulgite (APT) with AlCl₃ aqueous solution of various concentrations. The poly(acrylic acid)/Al³⁺‐attapulgite (PAA/Al³⁺‐APT) superabsorbent composite was prepared by reaction of partly neutralized acrylic acid, and Al³⁺‐APT in aqueous solution using N, N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. The surface morphology of the composite was investigated by SEM, and the Al³⁺‐APT composite generated a relatively planar surface comparing the nature APT. The effects of Al³⁺‐APT on hydrogel strength and swelling behaviors, such as equilibrium water absorbency, swelling rate, and reswelling capability, of the superabsorbent composites were also studied. The hydrogel strength and reswelling capability were improved, however, the equilibrium water absorbency and swelling rate decreased with increasing AlCl₃ solution concentration. The equilibrium water absorbency firstly increased, and then decreased with increasing Al³⁺‐APT content. The results indicate that Al³⁺‐APT acts as an assistant crosslinker in the polymeric network, which has great influences on hydrogel strength and swelling behaviors of the PAA/Al³⁺‐APT superabsorbent composites. POLYM. ENG. SCI., 47:619–624, 2007. © 2007 Society of Plastics Engineers.     

Highly stretchable,tough, and self‐recoverable and self‐healable dual physically crosslinked hydrogels with synergistic “soft and hard” networks

Strength, toughness and self‐recoverability are among the most important properties of hydrogels for tissue‐engineering applications. Yet, it remains a challenge to achieve these desired properties from the synthesis of a single‐polymer hydrogel. Here, we report our one‐pot, a monomer‐polymerization approach to addressing the challenge by creating dual physically crosslinked hybrid networks, in particular, synergistic “soft and hard” polyacrylic acid‐Fe³⁺ hydrogels (SHPAAc‐Fe³⁺). Favorable mechanical properties achieved from such SHPAAc‐Fe³⁺ hydrogels included high tensile strength (about 1.08 MPa), large elongation at break (about 38 times), excellent work of extension (about 19 MJ m^?3), and full self‐recoverability (100% recovery of initial properties within 15 min at 50°C and within 60 min in ambient conditions, respectively). In addition, the hydrogels exhibited good self‐healing capabilities at ambient conditions (about 40% tensile strength recovery without any external stimuli). This work demonstrates that dual physical crosslinking combining hydrophobic interaction and ionic association can be achieved in single‐polymer hydrogels with significantly improved mechanical performance but without sacrificing favorable properties. POLYM. ENG. SCI., 59:145–154, 2019. © 2018 Society of Plastics Engineers     

Catalytic potential of a poly(AAc‐co‐HPMA‐cl MBAm)‐matrix‐immobilized lipase from a thermotolerant Pseudomonas aeruginosa MTCC‐4713

A purified alkaline thermo‐tolerant lipase from Pseudomonas aeruginosa MTCC‐4713 was immobilized on a series of five noble weakly hydrophilic poly(AAc‐co‐HPMA‐cl MBAm) hydrogels. The hydrogel synthesized by copolymerizing acrylic acid and 2‐hydroxy propyl methacrylate in a ratio of 5 : 1 (HG_5:1 matrix) showed maximum binding efficiency for lipase (95.3%, specific activity 1.96 IU mg^?1 of protein). The HG_5:1 immobilized lipase was evaluated for its hydrolytic potential towards p‐NPP by studying the effect of various physical parameters and salt‐ions. The immobilized lipase was highly stable and retained ～92% of its original hydrolytic activity after fifth cycle of reuse for hydrolysis of p‐nitrophenyl palmitate at pH 7.5 and temperature 55°C. However, when the effect of pH and temperature was studied on free and bound lipase, the HG_5:1 immobilized lipase exhibited a shift in optima for pH and temperature from pH 7.5 and 55°C to 8.5 and 65°C in free and immobilized lipase, respectively. At 1 mM concentration, Fe³⁺, Hg²⁺, NH₄⁺, and Al³⁺ ions promoted and Co²⁺ ions inhibited the hydrolytic activities of free as well as immobilized lipase. However, exposure of either free or immobilized lipase to any of these ions at 5 mM concentration strongly increased the hydrolysis of p‐NPP (by ～3–4 times) in comparison to the biocatalysts not exposed to any of the salt ions. The study concluded that HG_5:1 matrix efficiently immobilized lipase of P. aeruginosa MTCC‐4713, improved the stability of the immobilized biocatalyst towards a higher pH and temperature than the free enzyme and interacted with Fe³⁺, Hg²⁺, NH₄⁺, and Al³⁺ ions to promote rapid hydrolysis of the substrate (p‐NPP). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4252–4259, 2006     

Energy transfer to Eu(III) in the solid‐state low‐density polyethylene–poly(acrylic acid) and low‐density polyethylene–Fe2O3–poly(acrylic acid) matrices

Ion exchange between H⁺ and Eu³⁺ and/or Tb³⁺ was studied in the material modified by in situ sorption and thermal polymerization of acrylic acid in low‐density polyethylene (LDPE–PAA) and in the composite system LDPE–Fe₂O₃–PAA. Fluorescence spectroscopy showed evidence of Eu³⁺ and/or Tb³⁺ ion exchanges in these materials. The matrix LDPE–PAA after Eu(III) ion exchange presented luminescence (excitation 265 nm). This was explained by an energy‐transfer process from the matrix LDPE–PAA to Eu³⁺ ions. The LDPE–PAA matrix after simultaneous Eu³⁺/Tb³⁺ ion exchange exhibited Eu³⁺ and Tb³⁺ ion luminescence (excitation 265 nm), confirming an energy‐transfer process from LDPE–PAA to Eu³⁺ ions in LDPE–PAA–Eu³⁺–Tb³⁺ matrix. Fe₂O₃ in LDPE–Fe₂O₃–PAA quenched the matrix for excitation at 265 nm and no emission at the region 400 nm was observed. The luminescence of Tb³⁺ ions in the matrix LDPE–Fe₂O₃–PAA–Tb³⁺ (excitation 265 nm) was partially quenched by Fe₂O₃. However, a weak emission of Eu³⁺ ions was observed (excitation 265 nm) in the matrix LDPE–Fe₂O₃–PAA after simultaneous Eu³⁺ and Tb³⁺ ion exchanges, suggesting an energy transfer from Tb³⁺ to Eu³⁺ ions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 919–931, 2000     

High‐Performance Flexible Sensors of Self‐Healing,Reversibly Adhesive,and Stretchable Hydrogels for Monitoring Large and Subtle Strains

Flexible sensors are becoming required in heath monitoring and human–machine interfaces, but it is still a challenge to develop flexible sensors with integrated high performances. Herein, high‐performance flexible sensors are fabricated that are self‐healing, reversibly adhesive, and utilizing stretchable hydrogels, which are composed of a pluronic F127 diacrylate (F127DA) cross‐linked poly(acrylic acid) (PAA) network and polydopamine (PDA), and further cross‐linked by Fe³⁺. The unique structure endows the resulting hydrogels (PAA‐PDA‐Fe³⁺ hydrogels) excellent self‐healing property, reversible adhesion property, mechanical stretchability, and electrical conductivity. On the basis of the excellent properties of PAA‐PDA‐Fe³⁺ hydrogels, flexible sensors with large sensing range (0–575%), high sensitivity (GF = 6.31), low response time (0.25 s), and excellent robustness (>500 cycles) are assembled and further applied in detecting both large and subtle strains induced by human motions and water ripple. Overall, this work not only provides an alternative clue to construct multi‐functional hydrogels, but also offers a new kind of high‐performance materials for flexible electronic devices, especially those for health monitoring and human–machine interface.     

Dual Cross‐Linked Hydrogels with High Strength,Toughness, and Rapid Self‐Recovery Using Dynamic Metal–Ligand Interactions

A dual cross‐linking design principle enables access to hydrogels with high strength, toughness, fast self‐recovery, and robust fatigue resistant properties. Imidazole (IMZ) containing random poly(acrylamide‐co‐vinylimidazole) based hydrogels are synthesized in the presence of Ni²⁺ ions with low density of chemical cross‐linking. The IMZ‐Ni²⁺ metal–ligand cross‐links act as sacrificial motifs to effectively dissipate energy during mechanical loading of the hydrogel. The hydrogel mechanical properties can be tuned by varying the mol% of vinylimidazole (VIMZ) in the copolymer and by changing the VIMZ/Ni²⁺ ratio. The resultant metallogels under optimal conditions (15 mol% VIMZ and VIMZ/Ni²⁺ = 2:1) show the best mechanical properties such as high tensile strength (750 kPa) and elastic modulus (190 kPa), combined with high fracture energy (1580 J m^?2) and stretchability (800–900% strain). The hydrogels are pH responsive and the extent of energy dissipation can be drastically reduced by exposure to acidic pH. These hydrogels also exhibit excellent anti‐fatigue properties (complete recovery of dissipated energy within 10 min after ten successive loading–unloading cycles at 400% strain), high compressive strength without fracture (17 MPa at 96% strain), and self‐healing capability due to the reversible dissociation and re‐association of the metal ion mediated cross‐links.     

Poly(vinyl alcohol)–Carbon Nanodots Fluorescent Hydrogel with Superior Mechanical Properties and Sensitive to Detection of Iron(III) Ions

A high‐strength fluorescent hydrogel is prepared by physical cross‐linking of carbon nanodots (CNDs) with poly(vinyl alcohol) (PVA). The stretching and compression of the PVA hydrogel are improved with CNDs by 176% and 64%, respectively. It still has excellent self‐healing behaviors without adding other healing agents. In addition, the search for rapid detection of heavy metals is still a huge challenge. The resulting hydrogel exhibits fluorescence quenching in the presence of Fe³⁺ by the fluorescence characteristics of CNDs, which has high selectivity and sensitivity. The PVA‐CNDs fluorescent hydrogel can be used as a solid detection platform for Fe³⁺, where the detection limit is found to be 10 µm for Fe³⁺ by fluorescence studies.     

A Facile Strategy for Preparing Tough,Self‐Healing Double‐Network Hyaluronic Acid Hydrogels Inspired by Mussel Cuticles

Compared with hydrogel‐like biological tissues such as cartilage, muscles, and blood vessels, current hyaluronic acid hydrogels often suffer from poor toughness and limited self‐healing properties. Herein, a facile and generalizable strategy inspired by mussel cuticles is presented to fabricate tough and self‐healing double‐network hyaluronic acid hydrogels. These hydrogels are composed of ductile, reversible Fe³⁺‐catechol interaction primary networks, and secondarily formed brittle, irreversible covalent networks. Based on this design strategy, the hyaluronic acid hydrogels are demonstrated to exhibit reinforced mechanical strength while maintaining a rapid self‐healing property. In addition, by simply regulating pH or UV irradiation time, the mechanical properties of the hydrogels can be regulated conveniently through variations between the primary and secondary networks.     

Binding behavior of Fe3+ ions on ion‐imprinted polymeric beads for analytical applications

We used a molecular imprinting approach to achieve specific metal binding utilizing N‐methacryloyl‐(L )‐cysteine methyl ester (MAC) as a metal‐complexing ligand. MAC was synthesized using methacryloyl chloride and cysteine methyl ester. Then, Fe³⁺ was complexed with MAC monomer. Fe³⁺‐imprinted poly(hydroxyethyl methacrylate‐N‐methacryloyl‐(L )‐cysteine methyl ester) [poly(HEMA‐MAC)] beads with average size of 63–140 μm were produced by suspension polymerization. After that, the template ions (i.e. Fe³⁺ ions) were removed by 0.1M HCl. Fe³⁺‐imprinted beads were characterized by swelling studies, FTIR, and elemental analysis. The Fe³⁺‐imprinted beads with a swelling ratio of 72%, and containing 3.9 mmol MAC/g were used in the binding of Fe³⁺ ions from aqueous solutions, tap water, certified reference serum sample, and real serum sample. Maximum binding capacity, optimum pH, and equilibrium binding time were 107 μmol/g, pH 3.0, and 30 min, respectively. It was observed that even in the presence of other ions, Fe³⁺‐imprinted beads selectively bound Fe³⁺ ions with 97% efficiency. Removal of Fe³⁺ ions from certified reference serum sample was approximately found to be 33%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3520–3528, 2006     

Nanoclay Reinforced Self‐Cross‐Linking Poly(N‐Hydroxyethyl Acrylamide) Hydrogels with Integrated High Performances

Despite recent significant progress in fabricating tough hydrogels, it is still a challenge to realize high strength, large stretchability, high toughness, rapid recoverability, and good self‐healing simultaneously in a single hydrogel. Herein, Laponite reinforced self‐cross‐linking poly(N‐hydroxyethyl acrylamide) (PHEAA) hydrogels (i.e., PHEAA/Laponite nanocomposite [NC] gels) with dual physically cross‐linked network structures, where PHEAA chains can be self‐cross‐linked by themselves and also cross‐linked by Laponite nanoplatelets, demonstrate integrated high performances. At optimal conditions, PHEAA/Laponite NC gels exhibit high tensile strength of 1.31 MPa, ultrahigh tensile strain of 52.23 mm mm^?1, high toughness of 2238 J m^?2, rapid self‐recoverability (toughness recovery of 79% and stiffness recovery of 74% at room temperature for 2 min recovery without any external stimuli), and good self‐healing properties (strain healing efficiency of 42%). The work provides a promising and simple strategy for the fabrication of dual physically cross‐linked NC gels with integrated high performances, and helps to expand the fundamentals and applications of NC gels.     

Highly Sensitive Detection of Fe3+ Ions Using Waterborne Polyurethane‐Carbon Dots Self‐Healable Fluorescence Film

In this study, nitrogen‐doped carbon dots (N‐C‐dots) are synthesized via a green and gentle electrochemical‐hydrothermal method. The N‐C‐dots are grafted into the backbone of waterborne polyurethane (WBPU) synthesized from hexamethylene diisocyanate and polycarbonate diol (PCDL). Due to the introduction of N‐C‐dots, the WBPU is functionalized including being able to self heal and specifically identified Fe³⁺. The self‐healing performance of the WBPU‐N‐C‐dots film is principally attributed to the hydrogen bonding effect of the WBPU and the N‐C‐dots. On the other hand, based on the quenching of fluorescent characteristics of the WBPU‐N‐C‐dots film, it is successfully used in the detection of Fe³⁺, showing a wide detection range, good selectivity, and high sensitivity. What's more, the tensile strength of the sample is enhanced from 3.50 to 7.12 MPa when the N‐C‐dots content is increased in the WBPU and the thermal stability is improved as a result of the formation of the more thermally‐stable network structures. Interestingly, compared to the traditional solution detection in WBPU‐N‐C‐dots emulsion with the limit of detection of 2.23 × 10^?6 m , the detection has the lower limit of detection of 2.19 × 10^?6 m in the WBPU‐N‐C‐dots film. These results show that the WBPU‐N‐C‐dots film exhibits great application as an intelligent response‐type material.     

Removal of heavy metal ions from aqueous solutions by radiation‐induced chitosan/(acrylamidoglycolic acid‐co‐acrylic acid) magnetic nanopolymer

An effective method was developed to isolate toxic heavy metal ions from the aqueous solution by the magnetic nanopolymers. The magnetic sorbent was prepared with radiation‐induced crosslinking polymerization of chitosan (CS), 2‐acrylamido‐glycolic acid (AMGA), and acrylic acid (AAc), which stabilized by magnetite (Fe₃O₄) as nanoparticles. The formation of magnetic nanoparticles (MNPs) into the hydrogel networks was confirmed by Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, and Scanning electron microscopy, which revealed the formation of MNPs throughout the hydrogel networks. The swelling behavior of the hydrogels and magnetic ones was evaluated at different pH values. The adsorption activity for heavy metals such as Cu²⁺ and Co²⁺ by nonmagnetic and magnetic hydrogels, Fe₃O₄/CS/(AMGA‐co‐AAc), in terms of adsorption amount was studied. It was revealed that hydrogel networks with magnetic properties can effectively be used in the removal of heavy metal ions pollutants and provide advantageous over conventional ones. POLYM. ENG. SCI., 55:1441–1449, 2015. © 2015 Society of Plastics Engineers     

A seawater‐assisted self‐healing metal–catechol polyurethane with tunable mechanical properties

Recently, self‐healing polymers have been one of the most intriguing academic fields due to the fact that they can increase their service lives and reduce the amount of waste. Here we designed and synthesized a novel telechelic polyurethane with dopamine (DA) end groups that are coordinated with Ca²⁺ to form dynamic non‐covalent bonds. The tensile stress of the designed polyurethanes increases with increase in the amount of metal cation added, while the strain at break slightly decreases. Rheological tests show that the ionic coordination between Ca²⁺ and catechol can dynamically break and recombine under the stimulation of seawater, endowing the polymer with superior self‐healing properties (up to 84% based on toughness). Therefore, the seawater‐triggered self‐healable, super tough polyurethane presented here is very intriguing as it has many potential applications especially in the marine environment. © 2019 Society of Chemical Industry     

Effect of attapulgite contents on release behaviors of a pH sensitive carboxymethyl cellulose‐g‐poly(acrylic acid)/attapulgite/sodium alginate composite hydrogel bead containing diclofenac

A series of pH‐sensitive composite hydrogel beads, carboxymethyl cellulose‐g‐poly(acrylic acid)/attapulgite/sodium alginate (CMC‐g‐PAA/APT/SA), were prepared by combining CMC‐g‐PAA/APT composite and SA, using Ca²⁺ as the ionic crosslinking agent and diclofenac sodium (DS) as the model drug. The effects of APT content and external pH on the swelling properties and release behaviors of DS from the composite hydrogel beads were investigated. The results showed that the composite hydrogel beads exhibited good pH‐sensitivity. Introducing 20% APT into CMC‐g‐PAA hydrogel could change the surface structure of the composite hydrogel beads, decrease the swelling ability, and relieve the burst release effect of DS. The drug cumulative release ratio of DS from the hydrogel beads in simulated gastric fluid was only 3.71% within 3 hour, but in simulated intestinal fluid about 50% for 3 hour, 85% for 12 hour, up to 90% after 24 hour. The obtained results indicated that the CMC‐g‐PAA/APT/SA hydrogel beads could be applied to the drug delivery system as drug carriers in the intestinal tract. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characteristics of poly(AAc5‐co‐HPMA3‐cl‐EGDMA15) hydrogel‐immobilized lipase of Pseudomonas aeruginosa MTCC‐4713

Four series of noble networks were synthesized with acrylic acid (AAc) copolymerized with varying amount of 2‐hydroxy propyl methacrylate or dodecyl methacrylate (AAc/HPMA or AAc/DMA; 5:1 to 5:5, w/w) in the presence of ethylene glycol dimethacrylate (EGDMA; 1, 5, 10, 15, and 20%, w/w) as a crosslinker and ammonium per sulfate (APS) as an initiator. Each of the networks was used to immobilize a purified lipase from Pseudomonas aeruginosa MTCC‐4713. The lipase was purified by successive salting out with (NH₄)₂SO₄, dialysis, and DEAE anion exchange chromatography. Two of the matrices, E_15a, i.e. [poly (AAc₅‐co‐DMA₁‐cl‐EGDMA₁₅)] and I_15c, i.e. [poly (AAc₅‐co‐HPMA₃‐cl‐EGDMA₁₅)], that showed relatively higher binding efficiency for lipase were selected for further studies. I_15c‐hydrogel retained 58.3% of its initial activity after 10th cycle of repetitive hydrolysis of p‐NPP, and I_15c was thus catalytically more stable and efficient than the other matrix. The I_15c‐hydrogel‐immobilized enzyme showed maximum activity at 65°C and pH 9.5. The hydrolytic activity of free and I_15c‐hydrogel‐immobilized enzyme increased profoundly in the presence of 5 mM chloride salts of Hg²⁺, NH₄⁺, Al³⁺, K⁺, and Fe³⁺. The immobilized lipase was preferentially active on medium chain length p‐nitrophenyl acyl ester (C:8, p‐nitrophenyl caprylate). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4636–4644, 2006     

POEGMA‐b‐PAA comb‐like polymer dispersant for Al2 suspensions

POEGMA‐b‐PAA comb‐like polymer is synthesized through RAFT polymerization, and it is employed as an efficient dispersant for Al₂O₃ suspensions. The POEGMA‐b‐PAA polymer consists of PAA chains and POEGMA comb‐like chains. The former provide electrostatic attraction between Al₂O₃ particles and polymer, while the latter extend to solution and maintain the stability of suspension due to strong steric hindrance. The adsorption is proven and the rheology behaviors of Al₂O₃ suspensions are strongly improved. Different POEGMA‐b‐PAA polymers with different length of side chains have similar but not identical rheological properties. The polymer with the appropriate length of side chain provides the biggest improvement to rheological properties of Al₂O₃ suspensions, such as apparent viscosity and granularity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43352.     

Properties and application of poly(methacrylic acid‐co‐dodecyl methacrylate‐cl‐N,N‐methylene bisacrylamide) hydrogel immobilized Bacillus cereus MTCC 8372 lipase for the synthesis of geranyl acetate

A range of fatty acid esters is now being produced commercially with immobilized microbial lipases (glycerol ester hydrolases; EC) in nonaqueous solvents. In this study, a synthetic hydrogel was prepared by the copolymerization of methacrylic acid and dodecyl methacrylate in the presence of a crosslinker, N,N‐methylene bisacrylamide. A purified alkaline thermotolerant bacterial lipase from Bacillus cereus MTCC 8372 was immobilized on a poly(methacrylic acid‐co‐dodecyl methacrylate‐cl‐N,N‐methylene bisacrylamide) hydrogel by an adsorption method. The hydrogel showed a 95% binding efficiency for the lipase. The bound lipase was evaluated for its hydrolytic potential toward various p‐nitrophenyl acyl esters with various C chain lengths. The bound lipase showed optimal hydrolytic activity toward p‐nitrophenyl palmitate at a pH of 8.5 and a temperature of 55°C. The hydrolytic activity of the hydrogel‐bound lipase was enhanced by Hg²⁺, Fe³⁺, and NH ions at a concentration of 1 mM. The hydrogel‐bound lipase was used to synthesize geranyl acetate from geraniol and acetic acid in n‐heptane. The optimization of the reaction conditions, such as catalyst loading, effect of substrate concentration, solvent (n‐pentane, n‐hexane, n‐heptane, n‐octane, and n‐nonane), reaction time, temperature, molecular sieve (3 Å × 1.5 mm) and scale up (at 50‐mL level), was studied. The immobilized lipase (25 mg/mL) was used to perform an esterification in n‐alkane(s) that resulted in the synthesis of approximately 82.8 mM geranyl acetate at 55°C in n‐heptane under continuous shaking (160 rpm) after 15 h when geraniol and acetic acid were used in a ratio of 100 : 100 mM. The addition of a molecular sieve (3 Å × 1.5 mm) to the reaction system at a concentration of 40 mg/mL in reaction volume (2 mL) resulted in an increase in the conversion of reactants into geranyl acetate (90.0 mM). During the repetitive esterification under optimum conditions, the hydrogel‐bound lipase produced ester (37.0 mM) after the eighth cycle of reuse. When the reaction volume was scaled up to 50 mL, the ester synthesized was 58.7 mM under optimized conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008