Uses of electron‐beam irradiation to prepare pH‐ and temperature‐sensitive hydrogels from reactive poly(vinyl alcohol) grafts

Thermosensitive poly(vinyl alcohol)‐graft‐(maleic anhydride), PVA‐MA, and poly(vinyl alcohol)‐graft‐(N‐isopropylacrylamide maleic anhydride) (PVA‐MA‐NIPAAm) copolymers containing carboxyl groups were prepared using electron beam irradiation at dose 80 kGy. The swelling ratios of the cross‐linked gels were measured at various temperatures. The LCST values were measured using DSC technique. The temperature dependence of the swelling ratios of the cross‐linked copolymers and terpolymers were measured at different temperatures. The swelling ratios of copolymers increased with increasing temperature up to 25–38°C, then decreased. The swelling behavior of both copolymers and terpolymers was referred to formation of hydrogen bonds between amide group of NIPAAm moieties and carboxyl group in MA moieties and to hydrophobic interaction due to methyl groups of NIPAAm. The swelling behaviors of these gels were analyzed in buffer solution at various pH. Swelling ratios of all gels were relatively high and they showed reasonable sensitive to pH. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Radiation synthesis and characterization of 2‐hydroxyethyl‐methacrylate‐based hydrogels containing di‐ and tri‐protic acid and its application on wastewater treatment

Radiation‐crosslinked 2‐hydroxyethylmethacrylate/citric acid (HEMA/CAc), 2‐hydroxyethylmethacrylate/tartaric acid (HEMA/TA), and 2‐hydroxyethylmethacrylate/succinic acid (HEMA/Sc) copolymers were prepared by using ⁶⁰Co γ‐rays. The gel fraction yield and the swelling behavior of the prepared hydrogels were studied. It was shown that increasing irradiation doses was accompanied by an increase in yield of gel fraction and a decrease in swelling degree. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, swelling exponent, and diffusion coefficient of the hydrogels were determined by studying the swelling behavior of the hydrogels prepared. It was seen that the equilibrium swelling degree increases as the content of acid increases, as a result of introducing more hydrophilic groups. When the hydrophilic polymer (acids) varies in the content range of 40–80 mg, swelling exponents (n) decreases, thereby indicating a shift in the water‐transport mechanism from the anomalous (non‐Fickian)‐type to the Fickian‐type. Characterization and some selected properties of the prepared hydrogels were studied, and accordingly the possibility of its practical use in the treatment of industrial wastes such as dyes and heavy metals (Fe, Ni, Co, and Cu) were also studied. The effect of treatment time, pH of feed solution, initial feed concentration, and temperature on the dye and heavy metals uptake was determined. The uptake order for a given metal was HEMA/TA hydrogel > HEMA/CAc > HEMA/Sc hydrogel. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Application of syndiotacticity‐rich PVA hydrogels prepared at a low temperature to thermo‐ and pH‐responsive release devices

Three kinds of physically cross‐linked syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA) hydrogels were prepared at 0°C with use of the buffer solutions (BS) of pHs 4.0, 7.4, and 9.0. Three gels swelled at first and then began to shrink after 12 h when they were dipped in the same BS for preparation at higher temperature than 0°C. The release of Brilliant Blue (3 mg/1 mL) from the cylindrical gels prepared using BS of pH 7.4 was studied at 27, 37, and 47°C. Brilliant Blue has been released spending 4–12 h almost completely. The rate of release from the gel at temperatures of 27, 37, and 47°C became large with increasing temperature. The main factor on release of Brilliant Blue is not the contraction of gel, but swelling, because the degree of swelling (DS) became large with increasing temperatures for 27, 37, and 47°C. The rate of release from the gel (pH 4.0) was larger than that (pH 7.4) due to the increased DS of the hydrogel in early step at pH of 4.0. The apparent diffusion exponents of these releases at pH 7.4 evaluated from first 60% of the fractional release were lower than 0.45 due to the swelling during release. The exponent at pH 4.0 was 0.45 due to immediate swelling. The on‐off of shrinking behavior of atactic PVA (a‐PVA) hydrogel was observed under several temperature changes. The rate of release of Brilliant Blue at 5°C was lower than that at 27°C and no change was observed at 5°C after one on‐off cycle. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 41–46, 2000     

Syndiotacticity‐rich ultrahigh molecular‐weight poly(vinyl alcohol) film. I. Determination of optimum polymer concentration by zone‐drawing method in film preparation

A new method using a simple zone‐drawing technique has been suggested for determining the optimum initial concentration of a polymer solution that has suitable macromolecular entanglements. This method was developed to replace the incorrect inherent viscosity‐measuring method for syndiotacticity‐rich (syndiotactic diad content of 63.4%) ultrahigh molecular‐weight (number‐average degree of polymerization of 12,300) (UHMW) poly(vinyl alcohol) (PVA) solution. Syndiotacticity‐rich UHMW PVA films were prepared from dimethyl sulfoxide (DMSO) solutions with different initial concentrations: of 0.1, 0.2, 0.3, 0.4, and 0.5 g/dL. In order to investigate the drawing behavior of the syndiotacticity‐rich UHMW PVA films with different solution concentrations, the films were drawn under various zone‐drawing conditions. Through a series of experiments, it was discovered that the initial concentration of PVA solution in DMSO caused significant changes in the draw ratio of the syndiotacticity‐rich UHMW PVA film. That is, the one‐step and maximum zone draw ratios of the film at an initial concentration of 0.3 g/dL exhibited its maximum values and gradually decreased at higher or lower concentrations. Thus, it was disclosed that the initial concentration of 0.3 g/dL is the optimum polymer concentration to produce a maximum draw ratio in this work. Based on the above results, it may be concluded that the optimum concentration of the initial PVA solution can be determined directly by measuring the zone draw ratio. The draw ratio, birefringence, crystallinity, degree of crystal orientation, tensile strength, and tensile modulus of the maximum drawn PVA film were 32.9, 0.0449, 0.61, 0.991, 1.91, and 46.2 GPa, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 123–134, 2000     

Synthesis and swelling properties of 2‐hydroxyethyl methacrylate‐co‐1‐vinyl‐3‐(3‐sulfopropyl)imidazolium betaine hydrogels

A series of 2‐hydroxyethyl methacrylate/1‐vinyl‐3‐(3‐sulfopropyl)imidazolium betaine (HEMA/VSIB) copolymeric gels were prepared from various molar ratios of HEMA and the zwitterionic monomer VSIB. The influence of the amount of VSIB in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures and the drug‐release behavior, compression strength, and crosslinking density were investigated. Experimental results indicated that the PHEMA hydrogel and the lower VSIB content (3%) in the HEMA/VSIB gel exhibited an overshooting phenomenon in their dynamic swelling behavior, and the overshooting ratio decreased with increase of the temperature. In the equilibrium water content, the value increased with increase of the VSIB content in HEMA/VSIB hydrogels. In the saline solution, the water content for these gels was not affected by the ion concentration when the salt concentration was lower than the minimum salt concentration (MSC) of poly(VSIB). When the salt concentration was higher than the MSC of poly(VSIB), the deswelling behavior of the copolymeric gel was more effectively suppressed as more VSIB was added to the copolymeric gels. However, the swelling behavior of gels in KI, KBr, NaClO₄, and NaNO₃ solutions at a higher concentration would cause an antipolyelectrolyte phenomenon. Besides, the anion effects were larger than were the cation effects in the presence of a common anion (Cl^?) with different cations and a common cation (K⁺) with different anions for the hydrogel. In drug‐release behavior, the addition of VSIB increased the drug‐release ratio and the release rate. Finally, the addition of VSIB in the hydrogel improved the gel strength and crosslinking density of the gel. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2888–2900, 2001     

Thermoreversible hydrogels X: Synthesis and swelling behavior of the (N‐isopropylacrylamide‐co‐sodium 2‐acrylamido‐2‐methylpropyl sulfonate) copolymeric hydrogels

A series of thermosensitive hydrogels were prepared from various molar ratios of N‐isopropylacrylamide (NIPAAm) and sodium‐2‐acrylamido‐2‐methylpropyl sulfonate (NaAMPS). Factors such as temperature and initial total monomer concentration and different pH solutions were investigated. Results indicated that the more the NaAMPS content in hydrogel system, the higher the swelling ratio and the gel transition temperature; the higher the initial monomer concentration, the lower the swelling ratio. The result also indicated that the NIPAAm/NaAMPS copolymeric hydrogels had different swelling ratios in various pH environments. The present gels showed a pH‐reversible property between pH 3 and pH 10 and thermoreversibility. The swelling ratios of copolymeric gels were lower in a strong alkaline environment because the gels were screened by counterions. Finally, the drug release behavior of these gels was also investigated in this article. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1760–1768, 2000     

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     

Preparations and properties of thermosensitive terpolymers of N‐isopropylacrylamide,sodium 2‐acrylamido‐2‐methyl‐propanesuphonate,and N‐tert‐butylacrylamide

Terpolymers based on N‐isopropylacrylamide, sodium 2‐acrylamido‐2‐methyl‐propanesulfonate, and N‐tert‐butylacrylamide were synthesized by free‐radical copolymerization with 2,2′‐azobisisobutyronitrile as an initiator. The lower critical solution temperatures (LCSTs) of the linear polymer aqueous solutions were determined by the measurement of the transmittance on UV at different temperatures. The influence of the polymer concentration, polymer composition, and ionic strength on the LCSTs of the linear polymers was investigated. The LCST decreased with increases in the hydrophobic monomer N‐tert‐butylacrylamide, polymer concentration, and ionic strength. The phase transition became sharp when the polymer concentration and ionic strength increased. Meanwhile, the crosslinked hydrogels were prepared with the same recipe used for the linear terpolymers, but a crosslinker was added to the reaction system. The swelling ratios of the hydrogels at various temperatures and salt solutions were determined. The hydrogels possessed both high swelling ratios and thermosensitivity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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     

Semi‐interpenetrating networks based on poly(N‐isopropyl acrylamide) and poly(N‐vinylpyrrolidone)

Three series of novel semi‐interpenetrating polymer networks, based on crosslinked poly(N‐isopropylacrylamide), PNIPA, and different amounts of the linear poly(N‐vinylpyrrolidone), PVP, were synthesized to improve the mechanical properties and thermal response of PNIPA gels. The effect of the incorporation of the linear PVP into the temperature responsive networks on the temperature‐induced transition, swelling/deswelling behavior, and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with varying molar ratios (25/1 to 100/1) of the monomer (N‐isopropylacrylamide) to the crosslinker (N,N′‐methylenebisacrylamide). The hydrogels were characterized by determination of the equilibrium degree of swelling, the dynamic shear modulus and the effective crosslinking density, as well as tensile strength and elongation at break. Furthermore, the deswelling kinetics of the hydrogels was studied by measuring their water retention capacity. The inclusion of the linear hydrophilic PVP in the PNIPA networks increased the equilibrium degree of swelling. The tensile strength of the semi‐interpenetrating networks (SIPNs) reinforced with linear PVP was higher than that of the PNIPA networks. The elongation at break of these SIPNs varied between 22% and 55%, which are 22 – 41% larger than those for pure PNIPA networks. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermoreversible hydrogels. VII. Synthesis and swelling behavior of poly(N‐isopropylacrylamide‐co‐3‐methyl‐1‐vinylimidazolium iodide) hydrogels

A series of N‐isopropylacrylamide/3‐methyl‐1‐vinylimidazolium iodide (NIPAAm/MVI) copolymer gels were prepared from the various molar ratios of NIPAAm, cationic monomer MVI, and N,N′‐methylene bisacrylamide (NMBA) in this study. The influence of the amount of MVI in the copolymer gels on the swelling behaviors was investigated in various aqueous saline solutions. Results showed that the swelling ratios (SRs) of copolymer gels were significantly greater than those of NIPAAm homopolymer gels, and the higher the MVI content, the higher the volume phase transition temperature. The SRs for the NIPAAm/MVI copolymer gels decreased with an increase of the salt concentration. In various saline solutions, results showed that the effect of divalent ions on the SR was greater than that of monovalent ions for these hydrogels. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3242–3253, 1999     

Colon‐specific oral delivery of vitamin B2 from poly(acrylamide‐co‐maleic acid) hydrogels: An in vitro study

Hydrogels, composed of poly(acrylamide‐co‐maleic acid) were synthesized and the release of vitamin B₂ from these gels was studied as a function of the pH of the external media, the initial amount of the drug loaded, and the crosslinking ratio in the polymer matrix. The gels containing 3.8 mg of the drug per gram gel exhibit almost zero‐order release behavior in the external media of pH 7.4 over the time interval of more than their half‐life period (t_1/2). The amount of the drug loaded into the hydrogel also affected the dynamic release of the encapsulated drug. As expected, the gels showed a complete swelling‐dependent mechanism, which was further supported by the similar morphology of the swelling and release profiles of the drug‐loaded sample. The hydrophilic nature of the drug riboflavin does not contribute toward the zero‐order release dynamics of the hydrogel system. On the other hand, the swelling osmotic pressure developed between the gels and the external phase, due to loading of the drug by equilibration of the gels in the alkaline drug solution, plays an effective role in governing the swelling and release profiles. Finally, the minimum release of the drug in the swelling media of pH 2.0 and the maximum release with zero‐order kinetics in the medium of pH 7.4 suggest that the proposed drug‐delivery devices have a significant potential to be used as an oral drug‐delivery system for colon‐specific delivery along the gastrointestinal (GI) tract. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1133–1145, 2002; DOI 10.1002/app.10402     

Preparation and swelling properties of semi‐IPN hydrogels based on chitosan‐g‐poly(acrylic acid) and phosphorylated polyvinyl alcohol

The phosphorylated poly(vinyl alcohol) (P‐PVA) samples with various substitution degrees were prepared through the esterification reaction of PVA and phosphoric acid. By using chitosan (CTS), acrylic acid (AA) and P‐PVA as raw materials, ammonium persulphate (APS) as an initiator and N,N‐methylenebisacrylamide as a crosslinker, the CTS‐g‐PAA/P‐PVA semi‐interpenetrated polymer network (IPN) ssuperabsorbent hydrogel was prepared in aqueous solution by the graft copolymerization of CTS and AA and followed by an interpenetrating and crosslinking of P‐PVA chains. The hydrogel was characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) techniques, and the influence of reaction variables, such as the substitution degree and content of P‐PVA on water absorbency were also investigated. FTIR and DSC results confirmed that PAA had been grafted onto CTS backbone and revealed the existence of phase separation and the formation of semi‐IPN network structure. SEM observations indicate that the incorporation of P‐PVA induced highly porous structure, and P‐PVA was uniformly dispersed in the polymeric network. Swelling results showed that CTS‐g‐PAA/P‐PVA semi‐IPN superabsorbent hydrogel exhibited improved swelling capability (421 g·g^?1 in distilled water and 55 g·g^?1 in 0.9 wt % NaCl solution) and swelling rate compared with CTS‐g‐PAA/PVA hydrogel (301 g·g^?1 in distilled water and 47 g·g^?1 in 0.9 wt % NaCl solution) due to the phosphorylation of PVA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tear force of physically crosslinked poly(vinyl alcohol) gels with different submicrometer‐scale network structures

Poly(vinyl alcohol) (PVA) gels can be easily prepared by either the freeze‐thawing (FT gel) method or by the cast‐drying (CD gel) method. Although the resulting nanostructured networks of the FT and CD gels are similar, their physical properties are quite different; while CD gels are transparent and elastic, FT gels are opaque and less elastic. Moreover, the tear energy of the FT gels is much greater than that of the CD gels, which is a direct result of micrometer‐scale differences in their network structures. In order to control the distribution of microcrystallites on nano‐ and micrometer scales, FT gels were prepared from PVA solutions with different water contents. As a result, the gel gradually became more transparent as the initial water content was decreased; and accordingly, the tear energy decreased. Tear resistance was improved in the case of FT gels by repeating the number of FT cycles, whereas with CD gels, this was achieved by increasing the gelation temperature. These results indicate that the microscopic network structures are characterized by a micrometer‐scale bundled‐polymer (fibril), which determines the tear energy of FT gels. Simple methods to control the fibril network structure of FT gels using a unidirectional freezing method are presented herein, with the swelling and mechanical properties of modified FT gels discussed in terms of their multiple‐scale network structures. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41356.     

Swelling and drug‐release behavior of the poly(AA‐co‐N‐vinyl pyrrolidone)/chitosan interpenetrating polymer network hydrogels

A series of novel hydrogels were prepared from acrylic acid (AA), N‐vinyl pyrrolidone (NVP), and chitosan by photopolymerization. The swelling behavior, gel strength, and drug release behavior of the poly(AA/NVP) copolymeric hydrogels and corresponding interpenetrating polymer network hydrogels were investigated. Results showed that the swelling ratios for the present hydrogels decreased with an increase of NVP content in the gel, but the gel strength increased with an increase of NVP content in the gel. Results also showed that the drug‐release behavior for the gels is related to the ionicity of drug and the swelling ratio of the gel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2135–2142, 2004     

Effects of synthesis‐solvent composition and initiator concentration on the swelling behaviour of poly(N‐isopropylacrylamide) P(NIPAAM), poly(NIPAAM‐co‐dimethyl itaconate), and poly(NIPAAM‐co itaconic acid) gels

The effects of synthesis‐solvent composition, initiator concentration, comonomer type and monomer purity on the volume swelling ratios, and polymer‐solvent interaction parameter χ have been investigated as a function of temperature. Non‐ionic N‐isopropylacrylamide (NIPAAM) homopolymer gels, poly[NIPAAM‐co‐(dimethyl itaconate)] (P(NIPAAM‐co‐DMI)) and poly[NIPAAM‐co‐(itaconic acid)] (P(NIPAAM‐co‐IA)) gels containing hydrophobic (DMI) and hydrophilic (IA) comonomers were prepared by free radical polymerization using potassium persulfate (KPS) –N, N, N′, N′‐tetramethyl ethylene diamine (TEMED) (redox initiator) in the presence of an N, N′‐methylene bis(acrylamide) (MBAAM) cross‐linking agent. The synthesis‐solvent composition (40/60 mixture of water/methanol and water) and initiator concentration employed significantly affected the properties of the NIPAAM gels. The transition temperatures of P(NIPAAM‐co‐IA) gels synthesized in water/methanol mixture were higher than that of the gel obtained in water. Furthermore, χ values of the NIPAAM homopolymer gel prepared with higher KPS content was an increasing function of temperature, while χ values of the sample obtained with lower initiator concentration changed around a critical solubility value 0.50. The results obtained also show that the interactions between monomer and solvent molecules in the reaction media (ie composition of the pregel solution) have an important effect on the formation and properties of the network structure (ie pore sizes of the gels). © 2000 Society of Chemical Industry     

Thermoreversible hydrogels. IX. Swelling behaviors of thermosensitive hydrogels copolymerized by N‐isopropylacrylamide with 1‐vinyl‐3‐(3‐sulfopropyl) imidazolium betaine

A series of thermosensitive hydrogels were prepared from the various molar ratios of N‐isopropylacrylamide, 1‐vinyl‐3‐(3‐sulfopropyl) imidazolium betaine (VSIB), and N,N′‐methylene‐bis‐acrylamide. The influence of the amount of VSIB in the copolymeric gels on the swelling behaviors in water, in various saline solutions, and at various temperatures was investigated. The results indicated that the higher the VSIB content in the hydrogel system, the higher the swelling ratio and the gel transition temperature. In the saline solution the results showed that when the concentration of salt is higher than the minimum salt concentration (MSC) of poly(VSIB), the deswelling behavior of the copolymeric gel was more effectively suppressed as more VSIB was added to the copolymeric gels. In addition, only the sample containing 12 mol % VSIB (V4) exhibited an antipolyelectrolyte's swelling behavior when the concentration of salt was higher than the MSC of poly(VSIB). This means that the swelling ratio of the hydrogel can be improved with a higher concentration salt solution. In addition, the anion effects were larger than the cation effects in the presence of a common anion (Cl⁻) with different cations and a common cation (K⁺) with different anions for the hydrogel. Finally, the more VSIB in the hydrogel, the higher the diffusion coefficient in dynamic swelling. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 14–23, 2000     

Starch‐poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropanesulfonic acid) graft copolymers prepared by reactive extrusion

Graft copolymers of starch with acrylamide and 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) were prepared by reactive extrusion in a twin‐screw extruder. The weight ratio of total monomer to starch was fixed at 1 : 3, while the molar fraction of AMPS in the monomer feed ranged from 0 to 0.119. Monomer to polymer conversions were 85% or greater, with grafting efficiencies of 68% (highest AMPS content) to 85% (no AMPS). Absorbency in distilled water at pH 7 increased linearly with the mole fraction AMPS in the grafted polymer, while absorbencies in 0.9% NaCl were independent of AMPS content. When swollen in water/ethanol mixtures, swelling decreased gradually with increasing ethanol volume fraction, followed by a large decrease over a narrow ethanol concentration. This behavior is similar to that observed for AMPS‐acrylamide gels. The swelling properties suggest these graft copolymers may have applications as responsive materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42405.     

Cellular PVA hydrogels produced by freeze/thawing

Cellular poly(vinyl alcohol) (PVA) hydrogels that exhibit enhanced swelling kinetics from an initial dry state were prepared by freezing and thawing techniques in the presence of NaCl. Gels that were dried immediately after preparation demonstrated a dual‐sorption effect upon swelling. Gels that were exposed to a 10‐day washing period to remove NaCl and excess PVA chains before drying showed an increased initial rate of swelling and overall water content. Freeze/thawed, cellular PVA gels showed overall enhanced swelling with increased mechanical strength over traditional gels prepared by chemical or irradiative crosslinking techniques. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2075–2079, 2000     

Preparation and optical properties of an all‐polymer light modulator using colored N‐isopropylacrylamide gel particles in a gel‐in‐gel system

A novel all‐polymer light modulator with a gel‐in‐gel system was developed. The gel‐in‐gel system was constructed with colored gel particles responsive to stimuli held independently in another stimuli‐nonresponsive gel matrix. Well‐known thermoresponsive N‐isopropylacrylamide (NIPAM) gel particles containing a pigment were dispersed and fixed in an outer stimuli‐nonresponsive gel matrix. When poly(vinyl alcohol)–styrylpyridinium (PVA–SbQ) was used for the outer gel matrix, the light modulator showed excellent color‐changing properties because the PVA–SbQ matrix was selectively formed around the NIPAM gel particles and the particles exhibited a large volume change in the matrix. The temperature when the outer gel matrix was formed affected the haze of the light modulator. When the outer gel matrix was formed in the swollen state of the NIPAM gels, the haze of a light modulator increased with heating. On the contrary, the haze of a light modulator prepared in the shrunken state of the NIPAM gels decreased with heating. The response time of the color change was less than 1 s. The gel‐in‐gel system made a very fast macroscopic color change, taking advantage of the fast response of the micrometer‐sized gel particles. We believe that a light modulator with a gel‐in‐gel system may find various applications in optical devices. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2295–2303, 2007