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Starch-based hydrogel containing azo group (SHA) was prepared through radical cross-linking reaction among starch- and PVA-based macromonomers, acrylic acid (AA) and 4-acryloyoxyazobenzene (AHAB). AHAB was prepared through an acylation reaction between acryloyl chloride and 4-hydroxyazobenzene (p-HAB), which was obtained by the diazo coupling reaction between aniline and phenol. The structure of SHA was confirmed with Fourier transform infrared spectrometer, thermogravimetric analysis and UV-Visible spectroscopy. SHA displayed pH-sensitive swelling in buffer saline. SHA film also exhibited a reversible trans-cis-trans photoisomerization behavior when they were subjected to alternative UV and visible light irradiation or dark storage. The dual-responsive characteristic was easily to be tailored via varying the initial amount of AHAB or AA., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A versatile water-soluble chitosan (WSC) was applied to construct two kinds of controllable functional hydrogels. Magnetic beads were prepared by physical cross-linking WSC with sodium alginate, soaking particles with ferrous chloride and being subjected to self-oxidation. Magnetic character of the beads was tunable by simply changing the initial concentration of ferrous ions. The beads could bind compounds that contained different charges. Their adsorption capacities for coomassie brilliant blue, rhodamine and hemoglobin were 1, 0.5 and 2.3mg/g respectively. Another kind of functional hydrogel was prepared through radical cross-linking reaction between WSC and a macromonomer (PVAM) derived from well-defined polyvinyl alcohol. The dynamic mechanical thermal analysis and thermogravimetric analysis results revealed that the mechanical strength and thermal stability of this hydrogel depended on the structure of PVAM. The capability to bind heavy metal ions of the hydrogel also relied on the structure of PVAM. The adsorption capacities of the hydrogels for Cu(2+) and Pb(2+) could reach 20.3 and 60.1mg/g respectively., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Tunable hydrogel that contained well-defined poly(vinyl alcohol) (PVA), labile lactate groups, and hydrophilic poly(ethylene glycol) (PEG) segments was prepared through a combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and esterification reaction. A diol was prepared via the esterification between lactic acid (LA) and PEG. Then the diol was allowed to react with maleic anhydride to produce a diacid. Meanwhile, well-defined PVA was synthesized by the alcoholysis of poly(vinyl acetate) (PVAc) obtained by RAFT polymerization of vinyl acetate. The hydrogels with tailor-made structure were generated by crosslinking PVA with LA-based diacid. The structures and properties of LA-based intermediates and the hydrogels were characterized with Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Both LA-based diol and diacid were semicrystalline and water-soluble, their melting temperature and glass transition temperature were 52 and −51, 54 and −41°C, respectively. The polydispersity indexes of the precursor of PVA samples were within the range of 1.03-1.10. It was found that the thermal stability of hydrogel was higher than that of LA-based diacid. Both the swelling and release properties of the hydrogels depend on the feeding ratio of PVA/LEM and the chain length of PVA, which reflected that the structure and properties of the hydrogels were controllable. POLYM. ENG. SCI., 54:1366-1371, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: The idea to develop hydrophilic lactic acid-based polyelectrolyte was presented. A facile route was utilized to prepare smart hydrogels that contained lactate units and carboxylic groups. The hydrogels were obtained through the radical cross-linking reaction between an unsaturated lactate-contained macromonomer and acrylic acid (AA)/itaconic acid (IA) monomer pair. The structure and performances of the hydrogels were characterized with thermogravimetric analysis, dynamic thermal analysis, scanning electron microscopy, swelling tests and adsorption measurements. The equilibrium swelling ratios of the hydrogels in acidic (pH 3.6) and basic (pH 11.5) media reached 25.3 and 62.3 respectively. The pH-sensitive swelling behaviors of the hydrogel confirmed that the hydrogels contained carboxylic groups and they were hydrophilic. The metal ions including calcium, copper, lead and cerium ions were bound into the hydrogels, which also confirmed the existence of the carboxyl groups. Moreover, the swelling ratio and adsorption capacity of the gel prepared from monomer pair were significantly higher than those obtained in absence of IA, which suggested that the properties of the hydrogels could be controllable by simply adjusting the ratio of AA/IA. In addition, the weight loss percentage of the hydrogel was around 37% after two-week in vitro degradation, which indicated the hydrogel contained lactate units. [Copyright &y& Elsevier]

Poly(vinyl alcohol) (PVA) was chosen as a controllable gelator to prepare sodium alginate (SA)-based physically cross-linked dual-responsive hydrogel by three steps. First, polyvinyl acetate (PVAc) was grafted onto SA via radical copolymerization. Then, the copolymer was subsequently converted into SA- g-poly(vinyl alcohol) (SAPVA) by alcoholysis reaction. PVA content of SAPVA was tailored by controlling the graft percentage of PVAc, i.e. through varying the amount of vinyl acetate during copolymerization. Finally, SAPVA hydrogels were formed by freezing-thawing cycles. The structure of the graft copolymers was verified with FTIR spectroscopy. X-ray diffraction analysis results revealed that the crystallinity of SAPVA hydrogels depended on the PVA content of SAPVA. The swelling test showed that SAPVA hydrogels were pH-responsive, and the swelling was reversible. SAPVA hydrogels also behaved electric-responsive. In addition, the pH-sensitivity of SAPVA hydrogels was able to be controlled with the composition of the hydrogels. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Abstract: A novel dual phase concomitant, methylcellulose sol@poly(vinyl alcohol) (MC/PVA) hydrogel, was prepared via physical mixing and subsequent freezing/thawing. MC/PVA hydrogel was stable within a wide temperature range, and exhibited reversible thermoresponsivity. The initial sol–gel transition temperatures of MC/PVA hydrogels containing 40, 45 and 50wt% MC were 45.9, 42.0 and 45.5°C, respectively. It was found that the crystallinity of these samples was 41.1%, 38.3% and 40.3%, respectively; all of them were lower than that of MC and PVA. The thermal responding rates of MC/PVA hydrogel composed of 30, 40, 45 and 50wt% MC were about 2.85, 3.17, 5.74 and 8.58%/min, respectively. The fluorescence micrograph and scanning electron microscopy of MC/PVA hydrogel revealed that the micro MC sol phases were dispersed in whole PVA network. Moreover, the thermal transition behavior and interior morphology of MC/PVA hydrogel could be tailored with its composition. [Copyright &y& Elsevier]

The article presents a study which examined the preparation of a series of physically crosslinked complex hydrogels of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) through physical mixing and a freeze/thaw technique. It analyzed the morphology of the CMC/PVA complex gels with differential scanning calorimetry and wide-angle X-ray diffraction. It found that the model drug hemoglobin was released completely from the complex hydrogels.

Abstract: Physically cross-linked starch-g-PVA hydrogels with controllable grafted branch length were prepared. Polyvinyl acetate (PVAc) was grafted onto starch via radical copolymerization. The molecular weight of PVAc was tailored using the chain transfer reaction. In consequence, the branch length of starch-g-PVA, which derived from starch-g-PVAc, could be easily controlled. In this paper, the viscosity average molecular weight of grafted PVA segment ranged from 1.3×104 to 7.2×104. The structure of grafted copolymers was verified with FTIR. XRD analysis showed the crystallinity of starch-g-PVA was lower than that of starch. Starch-g-PVA hydrogels were obtained by freezing and thawing. It was found that the swelling ratio of hydrogels increased with the molecular weight of PVA. [Copyright &y& Elsevier]

A novel degradable hydrogel has been prepared by condensing poly(vinyl alcohol) (PVA) with ELDA, a diacid derived from lactic acid. The structure of the ELDA crosslinking agent and the crosslinked PVA–ELDA polymer has been characterized with FTIR. The glass transition temperature (Tg) of PVA–ELDA, determined by DSC, is found to increase with the crosslink ratio (CR). The character of water in PVA–ELDA was also examined with DSC, which shows that the water in the hydrogel can be classified as bound and free water. The percentage of bound water in the hydrogel of CR 0.0151, 0.0101 and 0.0050 is 87.7, 74.5 and 76.4% respectively. The maximum equilibrium water content of the PVA–ELDA hydrogel is 123%. After 3-day''s immersion in phosphate-buffer saline (PBS) (0.1M, pH 7.4) at 37 °C, the maximum weight loss of PVA–ELDA is about 12.5%, which indicates it is degradable. [Copyright &y& Elsevier]