Relationship between water absorbency and reaction conditions in aqueous solution polymerization of polyacrylate superabsorbents

Polyacrylate superabsorbents were prepared by in situ aqueous solution polymerization in a polyethylene bag, which was submerged in a water bath. The influence of the initiator content, bath temperature, isopropanol content, initial monomer concentration, and crosslinker content (Cc) on water absorbency (Q) were investigated. The temperature change of the monomer mixture during polymerization was also analyzed. Increase of the chain ends in networks resulting from decrease of the molecular weight in free‐radical polymerization causes an increase of the water absorbency of superabsorbents and also reduces the crosslinking efficiency. The results are in conformity with the classical network theory. An empirical relation of Q = 2.45 Cc^−0.600 was obtained and the validity of Flory's swelling equation was confirmed indirectly. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 808–814, 2000     

Effect of poly(ethylene glycol)-derived crosslinkers on the properties of thermosensitive hydrogels

Three crosslinkers, poly(ethylene glycol) diacrylate (PEGDA), glycerol ethoxylate triacrylate (GETA) and citric acid-(PEG acrylate)₃ (CA-PEGTA) derived from poly(ethylene glycol) (PEG) were synthesized at first. The three series of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared by photopolymerization with the crosslinkers and compared with a hydrogel based on commercial crosslinker, N,N′-methylene bis-acrylamide (NMBA). The influence of the crosslinker structures and contents on the swelling behaviour, mechanical properties, and drug release of the hydrogels was investigated. The results showed that the hydrogels based on PEGDA and NMBA exhibited the highest and the lowest swelling ratio, respectively. The content of crosslinker of all hydrogel series showed good thermosensitivity and thermo-reversibility. The critical gel transition temperature (CGTT) appeared at 32 °C for the hydrogel based on NMBA, but appeared at about 34 °C for other hydrogels due to higher hydrophilicity of the crosslinker. In the mechanical properties, three-arms crosslinker GETA and CA-PEGTA led to higher mechanical strength than a linear crosslinker PEGDA. A hydrogel based on GETA (NG6) showed the highest shear modulus of 656.9 kPa and Young’s modulus of 1655.0 kPa. The hydrogels containing higher content of crosslinker revealed lower swelling ratio and higher mechanical strength. In the drug release, the hydrogels with higher swelling ratios showed higher drug absorbed. The highest release percentage of caffeine and vitamin B12 for hydrogel based on PEGDA (NP6) could reach 68.3% and 75.4%, respectively. In addition, the bound water and toxicity of the hydrogels were also investigated.

     

Water behavior of poly(vinyl alcohol)/poly(vinylpyrrolidone) interpenetrating polymer network hydrogels

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) and 1‐vinyl‐2‐pyrrolidone were prepared by radical polymerization with 2,2‐dimethoxy‐2‐phenylacetophenone as a photoinitiator and N,N′‐methylenebisacrylamide as a crosslinker. The IPN hydrogels were analyzed for the sorption behavior of water at 35°C and a relative humidity of 95% with a dynamic vapor sorption system, and water diffusion coefficients were calculated. Differential scanning calorimetry was used to quantitatively determine the amounts of freezing and nonfreezing water. The free‐water contents in the IPN hydrogel samples PV51, PV31, and PV11 were 74.40, 64.03, and 60.48% in pure water, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 24–27, 2003     

Network characteristics of homopolymer and some copolymers of poly(2-hydroxyethyl methacrylate)

Soluble poly(2-hydroxyethyl methacrylate) and copolymers of 2-hydroxyethyl methacrylate with n-butyl acrylate and 2-hydroxypropyl acrylate of varying compositions were synthesised by solution polymerisation. The polymers were characterised by dilute solution viscometry and shear viscosity. Crosslinked membranes were prepared from these polymers by introducing crosslinks in solution state through the reaction with 1,6-hexamethylene diisocyanate at a number of different crosslinker concentrations. The membranes swollen in dimethylformamide and water were characterised by performing equilibirium swelling measurements and calculating polymer volume fraction, the molecular mass between crosslinks (M?^c) and equilibrium water content (EWC) at 25°C. The calculation of M?^c used an expression developed by Peppas & Lucht for equilibrium swelling. This is a modified equation of the original Flory–Rehner expression, that allows non-Gaussian distribution of chain lengths. The variation of M?^c with crosslinker concentration and copolymer composition is discussed in terms of structural and molecular characteristics of these highly crosslinked networks.     

Synthesis of superabsorbent copolymers as water manageable materials

Strongly water‐absorbing polymers based on the monomers acrylamide, potassium acrylate and magnesium methacrylate were prepared by copolymerization using ammonium persulfate as initiator and N,N‐methylene‐bisacrylamide (MBA) as crosslinking agent. The copolymers are synthesized by varying monomer, crosslinker and initiator concentrations. The experimental results shows that superabsorbents (SAPs) have good absorbency both in water and NaCl solutions. The copolymers are characterized by IR spectroscopy. Water retention in soil is enhanced by use of these superabsorbents. The SAPs use for the growth of sunflower plants is also investigated. The water retention capacity of the SAPs was carried out at 60 °C and 100 °C. Copyright © 2003 Society of Chemical Industry     

Synthesis and characterization of poly(butylene terephthalate)‐co‐poly(butylene succinate)‐block‐poly(ethylene glycol) segmented block copolymers

Poly(butylene terephthalate)‐co‐poly(butylene succinate)‐block‐poly(ethylene glycol) segmented random copolymers, with poly(butylene succinate) (PBS) molar fraction (M_PBS) varying from 10 to 60 %, were synthesized through a melt polycondensation process and characterized by means of GPC, NMR, DSC and mechanical testing. The number‐average relative molecular mass of the copolymers was higher than 4 × 10⁴ g mol^?1 with polydispersity below 1.9. Sequence distribution analysis on the two types of hard segments by means of ¹H NMR revealed that the number‐average sequence length of PBT decreased from 2.80 to 1.23, while that of PBS increased from 1.27 to 4.76 with increasing M_PBS. The random distribution of hard segments was also justified because of the degree of randomness around 1.0. Micro‐phase separation structure was verified for the appearance of two glass transition temperatures and two melting points, respectively, in DSC thermograms of most samples. The crystallinity of hard segments changed with the crystallizability controlled by the average sequence length and reached the minimum value at an M_PBS of about 50–60 mol%. The results can also be ascribed to the co‐crystallization between two structurally analogous hard segments. Mechanical testing results demonstrated that incorporating a certain amount of PBS moieties (less than 30 mol%), at the expense of a minute depression of the elastic modulus, that higher relative elongation and more flexibility of polymer chain could be expected. Maximum equilibrium water absorption and faster degradation rates were observed on samples with higher M_PBS values and lower crystallinity of hard segments were better hydrophilicity of the polymer chain, through in vitro degradation experiments. Copyright © 2003 Society of Chemical Industry     

Polymer electrolyte membranes prepared by EB‐crosslinking of sulfonated poly(ether ether ketone) with 1,4‐butanediol

Crosslinked sulfonated poly(ether ether ketone) (SPEEK) membranes were prepared through the electron beam (EB)‐irradiation crosslinking of SPEEK/1,4‐butanediol under various irradiation conditions and used as a proton exchange membrane (PEM) for fuel cell applications. The crosslinked membranes were characterized by gel fraction, a universal testing machine (UTM), dynamic mechanical analysis (DMA), and small‐angle X‐ray scattering (SAXS). The gel fraction of the crosslinked membranes was used to estimate the degree of crosslinking, and the gel fraction was found to be increased with an increase of the crosslinker content and EB‐absorbed dose. The UTM results indicate that a brittle EB‐crosslinked membrane becomes more flexible with an increase in the crosslinker content. The DMA results show that the EB‐crosslinked membranes have well‐developed ionic aggregation regions and the cluster T_g of membranes decrease with an increase in the 1,4‐butanediol crosslinker content. The SAXS results show that the Bragg and persistence distance of crosslinked membranes increase with an increase in the crosslinker content. The proton conductivities of the EB‐crosslinked membranes were more than 9 × 10^?2 S/cm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41760.     

Sulfonated polyimide and poly (ethylene glycol) diacrylate based semi‐interpenetrating polymer network membranes for fuel cells

Semi‐interpenetrating polymer network (semi‐IPN) membranes based on novel sulfonated polyimide (SPI) and poly (ethylene glycol) diacrylate (PEGDA) have been prepared for the fuel cell applications. SPI was synthesized from 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid, and 2‐bis [4‐(4‐aminophenoxy) phenyl] hexafluoropropane. PEGDA was polymerized in the presence of SPI to synthesize semi‐IPN membranes of different ionic contents. These membranes were characterized by determining, ion exchange capacity, water uptake, water stability, proton conductivity, and thermal stability. The proton conductivity of the membranes increased with increasing PEGDA content in the order of 10^?1 S cm^?1 at 90°C. These interpenetrating network membranes showed higher water stability than the pure acid polyimide membrane. This study shows that semi‐IPN SPI membranes based on PEGDA which gives hydrophilic group and structural stability can be available candidates comparable to Nafion® 117 over 70°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Phase transition in swollen gels 30. Temperature-induced phase transition in positively charged poly(N-isopropylacrylamide) hydrogels in water and aqueous NaCl solutions

Summary The swelling and mechanical behaviour of ionized networks of N-isopropylacrylamide with an ionic comonomer, (2-acrylamidoethyl)trimethylammonium chloride (mole fractions x _S= 0−0.1), in the presence of a crosslinker, N,N'-methylenebisacrylamide, was investigated in water as a function of temperature and in aqueous NaCl solutions (c _NaCl= 10⁻⁵− 1 M) at 23 °C. On heating, a continuous decrease in the swelling degree in water, Q _w, was observed; increasing x _S shifts the volume transition temperature, T _tr, (from the swollen to collapsed state) to higher temperatures. The expected decrease in the swelling degree, Q, with increasing NaCl concentration in aqueous NaCl solutions was observed and two shrinking regions in ionic gels were found. The decrease in Q _w with increasing temperature and the decrease in Q with increasing c _NaCl are accompanied by an increase in equilibrium shear modulus of gels, so that the mechanical behaviour of gels is predominantly determined by the swelling degree. The experimental swelling behaviour could be, in the first approximation, described by the theory of polyelectrolyte networks in which repulsion of charges on the chain and finite chain extensibility were considered. Received: 7 June 2001 / Accepted: 21 September 2001     

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     

Superabsorbent polymeric materials IX: Effect of cationic structure on swelling behavior of crosslinked poly(sodium acrylate‐co‐cationic monomers) in aqueous salt solutions

Two series of xerogels based on sodium acrylate (SA), trimethyl methacrylamidopropyl ammonium iodide (TMMAAI), trimethyl methacryloyloxyethyl ammonium iodide (TMMAI), and N,N′‐methylene‐bis‐acrylamide (NMBA) as a crosslinker were prepared by inverse suspension polymerization. The water absorbency and swelling kinetic behavior for these xerogels in water or various saline solutions were investigated. The results showed that the swelling behaviors of these absorbents are related to their chemical structures, their compositions, and the type of external salt solutions. There would be effective improvement in the water absorbency of these two gel series by copolymerizing SA with a small amount of cationic monomer (TMMAAI or TMMAI). The initial absorption rates in deionized water were found to be faster for TM series gels than for TA series gels. The two series of superabsorbents had a tendency to absorb water in dilute nitrate aqueous solutions in the order: Fe³⁺, Ni²⁺, Ca²⁺, Cu²⁺, and Na⁺ for Fe(NO₃)₃, Ni(NO₃)₂, Ca(NO₃)₂, Cu(NO₃)₂, and NaNO₃ aqueous solution, respectively. The absorbency and initial absorption rate for these gels were related to the gel compositions and salt concentrations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1827–1837, 2001     

Preparation and swelling properties of solution crosslinked poly(cis‐1,4‐butadiene) gels

Poly(cis‐1,4‐butadiene) (PCB) gels were prepared by the crosslinking polymerization of 4‐tert‐butylstyrene (tBS) and divinylbenzene (DVB) onto unvulcanized butadiene rubber with a solution polymerization technique with benzoyl peroxide (BPO) as an initiator. The effects of the reaction conditions, such as the amount of the solvent, the amount of DVB and tBS, and the initiator (BPO), on the equilibrium swelling ratio (Q_e) were also investigated. The highest oil absorbencies of crosslinked gels in xylene and cyclohexane were 51.35 and 32.98 g/g, respectively. A swelling kinetic equation was proposed for this system: Q_t = Q_e ? {Kt + [1/(Q_e ? Q₀)]}^?1, where Q_t is the swelling ratio at time t, Q₀ is the initial swelling ratio, and K is the swelling kinetic constant. This equation fit the experimental results quite well. The diffusion of organic solvents in PCB gels was Fickian. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2241–2245, 2003     

Preparation and Swelling Behavior of Fast‐Swelling Superabsorbent Hydrogels Based On Starch‐g‐Poly(acrylic acid‐co‐sodium acrylate)

Summary: A novel fast‐swelling porous superabsorbent hydrogel was prepared by grafting acrylic acid onto corn starch through free‐radical polymerization in aqueous solution using N,N′‐methylenebisacrylamide as a crosslinker, ammonium persulfate as an initiator, sodium dodecyl sulfate and p‐octyl poly(ethylene glycol)phenyl ether as pore‐forming agents. The graft polymerization and surface morphology of the porous superabsorbents were characterized by FTIR and SEM. The results indicate that the porous superabsorbents were endowed with higher equilibrium water absorbency and faster swelling rate (they needed only 10 min to reach 90% of their equilibrium water absorbency) compared with the nonporous superabsorbents. The dewatering method employed had a significant influence on the swelling behavior of the superabsorbents and dewatering agents were useful to preserve the pores formed during the polymerization process.

The equilibrium water absorbency in distilled water, for the porous and non‐porous starch‐g‐poly(acrylic acid‐co‐sodium acrylate) superabsorbent hydrogels dried through different procedures.     

Synthesis and characterization of ABA type tri‐block copolymers derived from p‐dioxanone,L‐lactide and poly(ethylene glycol)

A series of triblock co‐polymers, consisting of a poly(ethylene glycol) (PEG) central block joined to two blocks of random p‐dioxanone‐co‐L ‐lactide copolymers were synthesized by ring‐opening polymerization of p‐dioxanone (PDO) and L ‐lactide (LLA) initiated by PEG in the presence of stannous 2‐ethylhexanoate catalyst. The resulting copolymers were characterized by various techniques including ¹H and ¹³C NMR and FTIR spectroscopies, gel permeation chromatography, inherent viscosity, wide‐angle X‐ray diffractometry (WAXD) and differential scanning calorimetry (DSC). The conversion of PDO and L ‐lactide into the polymer was studied various mole ratios and at different polymerization temperature from ¹H NMR spectra. Results of WAXD and DSC showed that the crystallinity of PEG macroinitiator was greatly influenced by the composition of PDO and L ‐lactide in the copolymer. The triblock copolymers with low molecular weight were soluble in water at below room temperature. © 2003 Society of Chemical Industry     

Photo‐crosslinked poly(ethylene glycol) diacrylate (PEGDA) hydrogels from low molecular weight prepolymer: Swelling and permeation studies

The aim of this work was to assess the diffusive properties of poly(ethylene glycol) diacrylate (PEGDA)‐based hydrogels, derived from low MW prepolymers, in view of potential biomedical applications. Several hydrogels were synthesized through UV irradiation of PEGDA solutions for different exposure times. Swelling measurements in distilled water were performed to estimate the yielded crosslink density, while swelling tests at 37 °C in selected media allowed to analyze the mesh size changes induced by various pH and ionic strength (IonS) conditions. The transport of glucose and insulin through thin hydrogel membranes was finally assessed in a modified Ussing chamber at physiological values of pH and IonS (7.4 and 150 mM, respectively). Results showed that the swelling was dependent on the IonS (with swelling reductions up to 20–30% for IonS increases in the range 0–300 mM) and, to a lesser extent, on the pH of the surrounding medium (with swelling increments of about 10% for increasing pH in the range 2.5–11). All hydrogels were also permeable to glucose and insulin, which displayed comparable diffusion coefficients (in the order of 10^?6 cm²/s). Specific interactions between glucose and the polymer chains were evidenced by values of the partition coefficient higher than unity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44380.     

Synthesis of copolymeric acrylamide/potassium acrylate hydrogels blended with poly(vinyl alcohol): Effect of crosslinking and the amount of poly(vinyl alcohol) on swelling behavior

A novel series of copolymeric acrylamide/potassium acrylate superabsorbents, blended with poly(vinyl alcohol), have been synthesized by using N, N′‐methylenebisacrylamide as a crosslinker and potassium persulphate (K₂S₂O₈) as an initiator. Swelling behavior of these hydrogels in water was investigated; and on the basis of swelling properties, the diffusional behavior of water into these hydrogel systems was analyzed. It was observed that with the increase of amount of poly(vinyl alcohol) or crosslinking, the swelling of the hydrogels decreased. The hydrogel synthesized by addition of 5% poly(vinyl alcohol) and 0.25% crosslinking showed maximum swelling of 54445%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1927–1931, 2005     

Facile UV‐curing technique to establish a 3D‐grafted poly(ethylene glycol) layer on an epoxy resin base for underwater applications

Construction of a highly hydrophilic polymer surface with excellent long‐term stability underwater is a great challenge. In this paper, a facile ultraviolet (UV) curing technique was employed to realize the three‐dimensional (3D) grafting of poly(ethylene glycol) diacrylate (PEGDA, molecular weight: 400, 600, and 1000 g/mol) on a bisphenol A epoxy acrylate (BEA) sheet. The cross section morphology, surface chemical composition, and wettability of the sheets were monitored using an optical microscope, an attenuated total reflectance Fourier transform infrared spectroscope, and a water contact angle analyzer, respectively. The PEGDA‐grafted epoxy sheets displayed a highly hydrophilic surface and meanwhile possessed excellent stability underwater, despite the molecular weight of PEGDA. In contrast, the PEGDA/BEA blend sheets are easily damaged underwater, due to strong swelling. In addition, the PEGDA1000‐grafted BEA sheet demonstrated good antifouling performance in a natural marine environment. Nevertheless, its long‐term antifouling is not satisfactory, being presumably due to hydrolysis or biodegradation of the PEG segments. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43972.     

Swelling behavior and determination of diffusion characteristics of acrylamide–acrylic acid hydrogels

In this study, a random copolymer of acylamide and acrylic acid [poly(AAm‐co‐AA)] was prepared by a redox copolymerization method of their aqueous solutions. The effects of initial AAm/AA mole ratio, PEG 4000 content, and N,N′‐methylenebisacrylamide concentration on swelling behavior were investigated in water. Average molecular weights between crosslinks, percentage swelling, swelling equilibrium values, and diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant) were evaluated for every hydrogel systems. The hydrogels showed mass swelling capabilities in the range 789–1040% (for AAm/AA hydrogels), 769–930% (for AAm/AA hydrogels in the presence of PEG 4000), and 716–1040% (for AAm/AA hydrogels containing different concentrations of the crosslinker). The swelling capabilities of the hydrogels decreased with the increasing AA, PEG 4000, and crosslinker concentrations. The diffusion of water into AAm/AA hydrogels was found to be a non‐Fickian type. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1289–1293, 2004     

Temperature‐responsive characteristics of poly(N‐isopropylacrylamide) hydrogels with macroporous structure

Macroporous poly(N‐isopropylacrylamide) (PNIPA) hydrogels were synthesized by free‐radical crosslinking polymerization in aqueous solution from N‐isopropylacrylamide monomer and N,N‐methylenebis (acrylamide) crosslinker using poly(ethylene glycol) (PEG) with three different number‐average molecular weights of 300, 600 and 1000 g mol^?1 as the pore‐forming agent. The influence of the molecular weight and amount of PEG pore‐forming agent on the swelling ratio and network parameters such as polymer–solvent interaction parameter (χ) and crosslinking density (ν_E) of the hydrogels is reported and discussed. Scanning electron micrographs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights and compositions of PEG during polymerization. At a temperature below the volume phase transition temperature, the macroporous hydrogels absorbed larger amounts of water compared to that of conventional PNIPA hydrogels, and showed higher equilibrated swelling ratios in aqueous medium. Particularly, the unique macroporous structure provides numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to external temperature changes during the swelling and deswelling process. These macroporous PNIPA hydrogels may be useful for potential applications in controlled release of macromolecular active agents. Copyright © 2006 Society of Chemical Industry