Gellan gum‐based novel composite hydrogel: Evaluation as adsorbent for cationic dyes

A semi‐interpenetrating network system [(GG‐g‐PAAm)‐PVA] was made by microwave irradiation of aqueous mixture of gellan gum (GG), acrylamide (AAm), and poly(vinyl alcohol) (PVA) containing N,N′‐methylene‐bis‐acrylamide as crosslinking agent. The gel was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, and scanning electron microscopy techniques. The swelling behavior was studied under different pH conditions. A pH‐dependent swelling with maximum swelling under neutral pH was observed. The swelling process is found to follow second‐order kinetics and the mechanism of water transport is found to be Fickian type of diffusion. The (GG‐g‐PAAm)‐PVA was evaluated for removal of dye from aqueous solution, using crystal violet, a cationic dye. The maximum adsorption capacity of the gel was found to be 45.45 mg/g. The kinetic studies revealed a second‐order adsorption process which fits well into Langmuir model. The evaluation of thermodynamic parameters indicated the adsorption process to be exothermic and spontaneous at lower temperatures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45527.     

Phase‐transfer‐agent‐aided polymerization and graft copolymerization of acrylamide

The use of phase‐transfer catalysts, with water‐insoluble initiators, for polymerization and graft copolymerization reactions was explored. The polymerization of a water‐soluble vinyl monomer, acrylamide (AAm), and the graft copolymerization of AAm onto a water‐insoluble polymer backbone, isotactic polypropylene (IPP), with a water‐insoluble initiator, benzoyl peroxide (BPO), and a phase‐transfer catalyst, tetrabutyl ammonium bromide (Bu₄N⁺Br^?), were carried out in a water/xylene binary solvent system. The conversion percentage of AAm into polyacrylamide (PAAm) and the percentage of grafting of AAm onto IPP were determined as functions of various reaction parameters, such as the BPO, AAm, and phase‐transfer‐catalyst concentrations, the amounts of water and xylene in the water/xylene mixture, the time, and the temperature. The graft copolymer, IPP‐g‐PAAm, was characterized with IR spectroscopy and thermogravimetric analysis. By a comparison of the results of the phase‐transfer‐catalyzed graft copolymerization of AAm onto IPP and the preirradiation method, it was observed that the optimum reaction conditions were milder for the phase‐transfer‐catalyst‐aided graft copolymerization. Milder reaction conditions, including the temperature, the time of reaction, and a moderate initiator (BPO), in comparison with high‐energy γ‐rays, led to better quality products, and the reaction proceeded smoothly with high productivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2364–2375, 2004     

Biodegradable poly(vinyl alcohol)‐graft‐ poly(ε‐caprolactone) comb‐like polyester: Microwave synthesis and its characterization

Poly(vinyl alcohol)‐initiated microwave‐assisted ring opening polymerization of ε‐caprolactone in bulk was investigated, and a series of poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) copolymers were prepared, with the degree of polymerization (DP) of PCL side chains and the degree of substitution (DS) of PVA by PCL being in the range of 3–24 and 0.35–0.89, respectively. The resultant comb‐like PVA‐g‐PCL copolymers were confirmed by means of FTIR, ¹H NMR, and viscometry measurement. The introduction of hydrophilic backbone resulted in the decrease in both melting point and crystallization property of the PVA‐g‐PCL copolymers comparing with linear PCL. With higher microwave power, the DP of PCL side chains and DS of PVA backbone were higher, and the polymerization reaction proceeded more rapidly. Both the DP and monomer conversion increased with irradiation time, while the DS increased first and then remained constant. With initiator in low concentration, the DP and DS were higher, while the monomer was converted more slowly. Microwaves dramatically improved the polymerization reaction in comparison of conventional heating method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3973–3979, 2007     

Viscometric,conductometric, and ultrasonic studies of gelatin-g-polyacrylamide composite

Polymerization of acrylamide in aqueous medium in the presence of gelatin has been carried out by the mutual method in air. All attempts to separate graft copolymer from the homopolymer and unreacted gelatin were unsuccessful as all the components were soluble in water. Hence the mixture comprising unreacted gelatin, homopolymer, polyacrylamide (PAAm), and the graft copolymer of gelatin and PAAm is referred to as the gelatin-g-PAAm composite. Solution properties of the composite with respect to viscosity, conductivity, and ultrasonic velocities were studied and the results were compared with those of PAAm prepared under identical conditions. © 1996 John Wiley & Sons, Inc.     

Polyvinyl Alcohol γ-Ray Grafted Nylon 4 Membrane for Pervaporation and Evapomeation

Abstract

Nylon 4, which possesses high mechanical strength and good affinity for water, can be considered as a liquid separation membrane. To improve the hydrophilicity of a Nylon 4 membrane for pervaporation and evapomeation processes, and to overcome the hydrolysis of polyvinyl alcohol (PVA), this study attempts to prepare a PVA-g-Nylon 4 membrane by γ-ray irradiation grafting of vinyl acetate (VAc) onto Nylon 4 membrane, followed by hydrolysis treatment. The effects of down-stream pressure, irradiation dose, VAc monomer concentration, degree of grafting, feed composition, and size of alcohols on the separation of water–alcohol mixtures were studied. The surface properties of the prepared membrane were characterized by FTIR, ESCA, and a contact angle meter. A separation factor of 13.8 and a permeation rate of 0.352 kg/m²·h can be obtained for a PVA-g-Nylon 4 membrane with a degree of grafting of 21.2% for a 90-wt% ethanol feed concentration. Compared to the pervaporation process, the evapomeation process has a significantly increased separation factor with a decreased permeation rate for the same PVA-g-Nylon 4 membrane.     

Studies of reactions with polymers. III. Syntheses and properties of poly(vinyl alcohol) graft terpolymers

A condensation-coupling reaction through esterification is performed between the hydroxy groups of poly(vinyl alcohol) (PVA) and the anhydride groups of methyl methacrylate (MMA)-co-maleic anhydride (MA) copolymer to produce the PVA-g-MMA/MA graft terpolymer. The MMA-co-MA copolymer was obtained by copolymerization of MA and MMA in dimethyl sulfoxide by using azobisisobutyronitrile as initiator. The structure of reaction products was confirmed by infrared analysis, and the dependence of composition, viscosity, and yield of the graft terpolymer on the MA content in MMA-co-MA as well as the concentration of the reactants fed were investigated. Mechanical properties, water content, and gel content of the membranes of terpolymers were measured over a wide range of compositions. PVA-g-MMA/N-ethylol maleimide was also synthesized by reacting the residual anhydride groups on PVA-g-MMA/MA with ethanol amine, this reaction proceeds through the PVA-g-MMA/N-ethylol maleamic acid intermediate.     

pH‐ and temperature‐sensitive in vitro release of salicylic acid through poly(vinyl alcohol‐g‐acrylamide) membranes

In this study, acrylamide (AAm) was grafted onto poly(vinyl alcohol) (PVA) in solution with UV radiation, and membranes were prepared from the graft copolymer (PVA‐g‐AAm) for transdermal release of salicylic acid (SA) at in vitro conditions. Permeation studies were carried out using a Franz‐type diffusion cell. Release characteristics of SA through PVA and PVA‐g‐AAm membranes were studied using 2.0 mg/mL SA solutions. Effects of the presence of AAm in the copolymer, pH of donor and acceptor solution, and concentration of SA and temperature on the release of SA were investigated. Permeation of SA through the membranes was found to be pH‐dependent, and increase in pH generally increased the release percentage of SA, and the presence of AAm in the membrane positively affected the permeation. The effect of concentrations of SA on the permeation was also searched using saturated solution of SA, and permeated amount of SA was found to be less than in the case of unsaturated SA solution. Studies showed that the release of SA from PVA‐g‐AAm membranes was temperature‐sensitive and increase in temperature increased the permeation rate. 82.76% (w/w) SA was released at the end of 24 h at (39 ± 1)°C, and the overall activation energy for the permeation of SA through PVA‐g‐AAm membranes was found to be 19.65 kJ/mol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Si@S-doped C anode with high cycling stability using PVA-g-PAA water soluble binder for lithium-ion batteries

The nanostructured Si@S-doped C (Si/C) hybrid is synthesized via a mild hydrothermal process of glucose and the simultaneous polymerization of 3,4-ethylenedioxythiophene and poly(sodium-4-styrene sulfonate) on the surface of nano-Si powders, then followed by a calcination process. A new water soluble polymer of poly(vinyl alcohol) (PVA) grafted with poly(acrylic acid) (PAA) is synthesized via a free-radical polymerization of acrylic acid (AA) in a 1:1 weight ratio in PVA water solution. The Si/C anode using PVA-g-PAA binder, exhibits improved lithium storage properties and cycling stability than that of the parallel electrode with carboxymethyl cellulose binder, which exhibits an initial coulombic efficiency (82.0%), even a reversible capacity of 487 mAh g⁻¹ after 300 cycles with 81.2% capacity retention at 0.4 A g⁻¹. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48764.     

Plasma‐induced solid‐state polymerization modified poly(tetrafluoroethylene) membrane for pervaporation separation of aqueous alcohol mixtures

Acrylamide (AAm) solid state polymerization was induced using argon plasma to improve the pervaporation performance of poly(tetrafluoroethylene) (PTFE) membranes (PTFE‐g‐PAAm) in aqueous alcohol mixtures. The surface morphology, chemical composition, and hydrophilicity changes in the PTFE and PTFE‐g‐PAAm membranes were investigated using ATR‐FTIR, SEM, AFM, X‐ray photoelectron spectroscopy, and water contact angle measurements. The surface hydrophilicity rapidly increased with increasing Ar exposure time, but decreased after longer Ar exposure time because of the degradation in the PTFE‐g‐PAAm membrane grafted layer. Compared with the hydrophilicity of the pristine PTFE membrane (water contact angle = 120°), the argon plasma induced acrylamide (AAm) solid‐state polymerization onto the PTFE surface (water contact angle = 43.3°) and effectively improved the hydrophilicity of the PTFE membrane. This value increases slowly with increasing aging time and then reaches a plateau value of about 50° after 10 days of storage under air. The pervaporation separation performances of the PTFE‐g‐PAAm membranes were higher than that of the pristine PTFE membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:909–919, 2006     

Synthesis of high-molecular weight poly(vinyl alcohol) by low-temperature emulsifier-free emulsion polymerization of vinyl acetate and saponification

High-molecular weight (HMW) poly(vinyl alcohol) (PVA) was prepared via an emulsifier-free emulsion polymerization of vinyl acetate (VAc) using a redox initiation system in low temperatures, and the subsequent saponification with potassium hydroxide in methanol. The effect of the polymerization conditions on the conversion, molecular weight, and branching degree was investigated. PVA with maximum viscosity-average degree of polymerization (DP) of 8270 could be prepared by saponification of poly(vinyl acetate) (PVAc), with DP of 10,660 obtained at temperature of 10°C, monomer concentration of 30%, potassium persulfate molar ratio to monomer of 1/2000, agitation speed of 160 rpm. The conversion was above 90%. From the emulsifier-free emulsion polymerization of VAc in low temperature, PVAc with HMW and high linearity was effectively prepared, which might be useful for the preparation of high-strength and high-modulus PVA fiber. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Formation and structure of polyacrylamide gels

Acrylamide and N,N′-methylenebis (acrylamide) (AAm–Bis) copolymerization has been in-vestigated in water at a monomer concentration of 1.8 w/v%. Conversion of monomer and pendant vinyl groups was measured as a function of the reaction time up to the onset of macrogelation. Experimental results indicate that 80% of pendant vinyl groups are consumed by cyclization reactions. When the monomer concentration was kept constant at 1.8%, the critical conversion at the gel point shows a minimum at 7.5 mol % Bits. The equilibrium degree of swelling of the polyacrylamide (PAAm) gels is independent of their crosslinker content. Calculation results show that the average reactivity of pendant vinyl groups for intermolecular links decreases as the Bis concentration increases. All these results suggest formation of PAAm microgels prior to the onset of macrogelation. As the reaction proceeds, microgels are connected to a macrogel through their peripheral pendant vinyls and radical ends, whereas those in their interior remain intact. The microgels seem to act as the junction points of the final inhomogeneous networks. © 1996 John Wiley & Sons, Inc.     

Green synthesis of porous polyvinyl alcohol membranes functionalized with l-arginine and their application in the removal of 4-nitrophenol from aqueous solution

Green and single-step synthesis of porous poly(vinyl alcohol) membrane functionalized with l -arginine (PVA-g-Arg) is presented. Crosslinking, l -arginine functionalization and pore forming occurred simultaneously by a thermally induced process without using a crosslinker or an initiator. As-synthesized PVA-g-Arg membranes possessed a porous structure with an average pore size of 32–56 μm depending on the amount of l -arginine. The PVA-g-Arg were utilized as adsorbent membranes for the removal of 4-nitrophenol (4-NP) from aqueous solutions and demonstrated higher adsorption capacity than that of the unmodified PVA porous membrane. The pseudo-second-order described satisfactorily the kinetic adsorption of 4-NP by the membranes while the isotherms followed both the Langmuir and Freundlich models. The negative values of ΔG° and thermodynamic parameters confirmed that the adsorption of 4-NP by the PVA-g-Arg membranes was spontaneous and exothermic. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47835.     

Viscometric studies of starch-g-polyacrylamide composites

Composites of starch-g-polyacrylamide, starch, and polyacrylamide have been prepared by gamma radiation-initiated polymerization of acrylamide in the presence of starch in aqueous medium. The polymerization was studied as a function of the (i) amount of water (ii) monomer concentration, and (iii) total dose. The optimum conditions for maximum conversion of the monomer to homopolymer and graft copolymer have been evaluated. Percentage of grafting of polyacrylamide could not be determined precisely as both the homopolymer and the graft are soluble in common solvents and all attempts to separate the graft from the homopolymer were unsuccessful. However, the formation of the starch-g-polyacrylamide copolymer was confirmed by the turbidimetric studies using acetone as a nonsolvent. The products of polymerization of acrylamide in the presence of starch consisted of unreacted starch, starch-g-polyacrylamide, and polyacrylamide and is referred to as the composite. Acrylamide was also polymerized in the absence of starch using γ-rays as means of initiation and the optimum conditions for maximum conversion of acrylamide to polyacrylamide have been evaluated. Viscosity behavior of the composite and polyacrylamide was studied in aqueous medium at 30±0.04°C. The reduced specific viscosity of the aqueous solution of acrylamide and the composite as well was found to increase with increasing dilution, the effect being more pronounced in the composite. This tends to indicate that both the homopolymer and the composite behave as polyelectrolytes. An attempt has been made to explain the polyelectrolytic behavior of the homopolymer and the composite. © 1993 John Wiley & Sons, Inc.     

Synthesis of syndiotacticity‐rich high molecular weight poly(vinyl alcohol) by suspension polymerization of vinyl pivalate and saponification

Vinyl pivalate (VPi) was suspension‐polymerized to synthesize high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with a high conversion above 95% for a precursor of syndiotacticity‐rich HMW poly(vinyl alcohol) (PVA). Also, the effects of the polymerization conditions on the conversion, molecular weight, and degree of branching (DB) of PVPi and PVA prepared by the saponification of PVPi were investigated. Bulk polymerization was slightly superior to suspension polymerization in increasing the molecular weight of PVA. On the other hand, the latter was absolutely superior to the former in increasing the conversion of the polymer, indicating that the suspension polymerization rate of VPi was faster than that of the bulk one. These effects could be explained by a kinetic order of a 2,2′‐azobis(2,4‐dimethylvaleronitrile) concentration calculated by the initial rate method. Suspension polymerization of VPi at 55°C by controlling various polymerization factors proved to be successful in preparing PVA of HMW [number‐average degree of polymerization (P_n): 8200–10,500], high syndiotactic diad content (58%), and very high yield (ultimate conversion of VPi into PVPi: 94–98%). In the case of the bulk polymerization of VPi at the same conditions, the maximum P_n and conversion of 10,700–11,800 and 32–43% were obtained, respectively. The DB was lower and the P_n was higher with PVA prepared from PVPi polymerized at lower initiator concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 832–839, 2003     

Graft polymerization of vinyl acetate onto starch. Saponification to starch–g–poly(vinyl alcohol)

Graft polymerizations of vinyl acetate onto granular corn starch were initiated by cobalt-60 irradiation of starch-monomer-water mixtures, and ungrafted poly(vinylacetate) was separated from the graft copolymer by benzene extraction. Conversions of monomer to polymer were quantitative at a radiation dose of 1.0 Mrad. However, over half of the polymer was present as ungrafted poly-(vinyl acetate) (grafting efficiency less than 50%), and the graft copolymer contained only 34% grafted synthetic polymer (34% add-on). Lower irradiation doses produced lower conversions of monomer to polymer and gave graft copolymers with lower % add-on. Addition of minor amounts of acrylamide, methyl acrylate, and methacrylic acid as comonomers produced only small increases in % add-on and grafting efficiency. However, grafting efficiency was increased to 70% when a monomer mixture containing about 10% methyl methacrylate was used. Grafting efficiency could be increased to over 90% if the graft polymerization of vinyl acetate-methyl methacrylate was carried out near 0°C, although conversion of monomers to polymer was low and grafted polymer contained 40-50% poly(methyl methacrylate). Selected graft copolymers were treated with methanolic sodium hydroxide to convert starch–g–poly(vinyl acetate) to starch–g–poly(vinyl alcohol). The molecular weight of the poly(vinyl alcohol) moiety was about 30,000. The solubility of starch–g–poly(vinyl alcohol) in hot water was less than 50%; however, solubility could be increased by substituting either acid-modified or hypochlorite-oxidized starch for unmodified starch in the graft polymerization reaction. Vinyl acetate was also graft polymerized onto acid-modified starch which had been dispersed and partially solubilized by heating in water. A total irradiation dose of either 1.0 or 0.5 Mrad gave starch–g–poly(vinyl acetate) with about 35% add-on, and a grafting efficiency of about 40% was obtained. A film cast from a starch–g–poly(vinyl alcohol) copolymer in which homopolymer was not removed exhibited a higher ultimate tensile strength than a comparable physical mixture of starch and poly(vinyl alcohol).     

Degradation on polyacrylamides. Part II. Polyacrylamide gels

The stability of polyacrylamide (PAAm) gels, synthesized by free radical polymerization of acrylamide (AAm) and N,N′-methylenebisacrylamide (BIS), was investigated when subjected to thermal and irradiation conditions. The PAAm gels were stable and did not release AAm under fluorescent light. In aqueous solution at 95 °C, a small amount of AAm was observed and it is shown that this is found from the pendant unsaturation of BIS in the gel network. Under UV irradiation, approximately one molecule of AAm is released for every 20,000 repeat monomer units in the gel. Gels were also synthesized from methacrylamide with BIS, AAm with N,N′-methylenebismethacrylamide and AAm with bisacryloyl-piperazine. Their stability is compared to the AAm/BIS gels.     

Mechanical and tribological behaviors of PVA/PAAm double network hydrogels under varied strains as cartilage replacement

The strain change of double network (DN) hydrogels during compressive mechanical and frictional tests is crucial for their performances. The positive effect of the sacrificed network for prohibiting crack in DN hydrogel is likely to be initiated by large strain. In this study, the mechanical and tribological properties of polyvinyl alcohol/polyacrylamide (PVA/PAAm) DN hydrogels are investigated from the viewpoint of strain. The compressive tangent modulus of PVA/PAAm DN hydrogel with 15 wt% AAm shows a sudden increase in the strain of 60% due to the sacrificed PAAm network. The optimized friction behavior is obtained from PVA/PAAm hydrogel with 5 wt% of AAm content, which is not consistent with the optimal compressive modulus at 15 wt% of AAm content. The variation of frictional coefficient of PVA/PAAm DN hydrogels with load is quite different for migrating and stationary contact configurations. The biphasic lubrication mechanism transited to solid–solid contact dominant mechanism is also induced by the high strain at heavy load.     

Sorption of Methylene Blue onto Ionic Composite Hydrogels Based on Polyacrylamide and Dextran Sulfate: Kinetics,Isotherms, and Thermodynamics

Ionic composite hydrogels based on polyacrylamide (PAAm) and dextran sulfate (DxS) have been prepared by radical polymerization at two temperatures: +20°C and ?18°C, using DxS as physical entrapped polymer, acrylamide (AAm) monomer, N,N^’-methylenebis(acrylamide) (BAAm) as cross-linking agent, ammonium persulfate as radical initiator, and N,N,N’,N’-tetramethylethylenediamine as accelerator of free-radical polymerization. The PAAm/DxS composite hydrogels were tested as sorbents for Methylene Blue (MB) from aqueous solution by the batch procedure. The effect of contact time, initial dye concentration, and temperature on the dye sorption onto composite hydrogels has been investigated. The modeling of the experimental data by applying different kinetic and isotherm models was also performed.     

Preparation of high molecular weight poly(vinyl pivalate) with high yield and high molecular weight poly(vinyl alcohol) by emulsion polymerization of vinyl pivalate and saponification

To prepare high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with high yield and high linearity which is a promising precursor for syndiotactic poly (vinyl alcohol) (PVA), vinyl pivalate (VPi) was emulsion polymerized, using 2,2′‐azobis(2‐amidinopropane) dihydrochloride (AAPH) as an initiator and sodium dodecyl sulfate (SDS) as an emulsifier. The effect of the polymerization conditions on the conversion, molecular weight, and degree of branching was investigated. PVA with maximum number‐average degree of polymerization (P_n) of 6200 could be prepared by complete saponification of PVPi, with P_n of 13,300–16,700 obtained at polymerization temperature of 50°C, using SDS and AAPH concentration of 2.0 × 10^?3 mol/L of water and 1.0 × 10^?3 mol/L of water, respectively, and the maximum conversion was about 90%. From the emulsion polymerization of VPi, spherical PVPi with high yield was effectively prepared, which might be useful for the precursor of syndiotactic PVA micro‐ and nano‐spheres with various surface properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 410–414, 2007     

Synthesis,characterization, and swelling behavior of poly(N-hydroxymethylacrylamide) grafted poly(vinyl alcohol)

In this study, the graft copolymerization of N-hydroxymethylacrylamide (NHMAAm) with poly(vinyl alcohol) (PVA) was carried out by using potassium persulfate/N,N,N,N-tetramethylethylenediamine (K₂S₂O₈) to improve physicochemical properties and functionality of PVA. The structures of PVA-g-poly-NHMAAm (PNHMAAm) copolymers were characterized by Fourier transform infrared, elemental analysis, nuclear magnetic resonance (¹H-NMR), ¹³C-NMR, and size exclusion chromatography. Their thermal behaviors were investigated by differential scanning calorimetry and thermogravimetric analysis (TGA). The TGA results indicated that the graft copolymers show better thermal stability then PVA. The effects of reaction time, temperature, NHMAAm, and K₂S₂O₈ concentrations on grafting parameters were examined. The maximum grafting yield (34.01%) was provided when reaction was carried out under optimum conditions (time = 2 hr, T = 40°C, [NHMAAm] = 0.25 M, [K₂S₂O₈] = 4.56 × 10⁻³ M). Moreover, PVA-g-PNHMAAm membranes were prepared and their swelling behaviors were studied. The results demonstrated that swelling degree of graft membranes increased almost 3.5-fold compared to PVA membrane.