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Hydrogel sensors are well suited to measuring the concentration of substances in liquids, and, because the hydrogel is biocompatible, they are ideal for medical use. Hydrogels change their volume in response to stimuli. The larger the hydrogel, the more pronounced the measurement signal. However, a larger volume also leads to slower swelling due to the longer diffusion paths. One method of determining the degree of swelling is to measure the swelling pressure using a piezoresistive pressure sensor. With current approaches, measurement times of several minutes can be achieved. By exploiting the bimorph effect, we were able to reduce the thickness of the hydrogel and, thus, reduce the response time of the entire sensor to less than 1 min. The aim of this paper is now to show how a sensor with short response times can be designed and manufactured and, in particular, how to find a suitable hydrogel composition, how to appropriately structure the hydrogel layer and how a robust adhesion of the hydrogel to the sensor chip can be achieved. As a result, we were able to show that such hydrogel sensors with response times of just a few seconds are possible.

Ion-exchange membranes (IEMs) are a core component that greatly affects the performance of electrochemical energy conversion processes such as reverse electrodialysis (RED) and all-vanadium redox flow battery (VRFB). The IEMs used in electrochemical energy conversion processes require low mass transfer resistance, high permselectivity, excellent durability, and also need to be inexpensive to manufacture. Therefore, in this study, thin-reinforced anion-exchange membranes with excellent physical and chemical stabilities were developed by filling a polyethylene porous substrate with functional monomers, and through in situ polymerization and post-treatments. In particular, the thin-reinforced membranes were made to have a high ion-exchange capacity and a limited degree of swelling at the same time through a double cross-linking reaction. The prepared membranes were shown to possess both strong tensile strength (>120 MPa) and low electrical resistance (

Изучены сорбционные свойства пленок на основе модифицированного поливинилового спирта. Получены кривые, характеризующие кинетику набухания пленок модифицированного ПВС в воде. Показана способность гидрогелей ПВС удерживать влагу и отдавать ее в концентрированный солевой раствор, имитирующий почвенный раствор., The sorption properties of films based on modified polyvinyl alcohol were studied. Curves characterizing the swelling kinetics of modified PVA films in water are obtained. The ability of PVA hydrogels to retain moisture and transfer it to a concentrated salt solution that simulates a soil solution is shown.

Herein we report on the preparation and structural characterization of six amphiphilic polymer conetworks (APCN) based on end-linked amphiphilic “core-first” star block copolymers, comprising methyl methacrylate and 2-(dimethylamino)ethyl methacrylate as the monomer repeating units in the hydrophobic and hydrophilic blocks, respectively. The various APCNs differed either in the arm composition or in the arm molecular weight. APCN synthesis was accomplished via the one-pot, sequential group transfer polymerization (GTP) of cross-linker, hydrophobic monomer, hydrophilic monomer, and cross-linker again. The soluble precursors to the APCNs, i.e., the star homopolymers, the star block copolymers and the initial cross-linker cores, were characterized in terms of their composition, size and size dispersity. The degrees of swelling in tetrahydrofuran were found to increase with the molecular weight of the arms of the stars of the APCNs, whereas the degrees of swelling in water increased with the content in hydrophilic units in the arms of the constituting stars. Small-angle neutron scattering (SANS) indicated that most APCNs nanophase separated in D2O. The structure and size of the hydrophobic domains determined by fitting the SANS data to an appropriate model could be correlated with the molecular architecture of the APCNs. Finally, polarized light microscopy showed that all APCNs were birefringent both in water and in the dried state. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 372 1 69 86

Glycerol (G, a triol) and sebacic acid (S, an α,ω-dicarboxylic acid) were condensed in the bulk to obtain poly(glycerol sebacate) (PGS) cross-linked elastomers which were characterized in terms of their swelling, thermal, and mechanical properties. The soluble precursors to the elastomers were characterized in terms of their size, size distribution, and composition. In particular, G-S mixtures of five different compositions (molar G:S ratio = 2:1, 2:2, 2:3, 2:4, and 2:5) were copolymerized in the bulk at 120 C in a three-step strategy (first step under inert gas atmosphere, followed by two steps in vacuo). When the G:S molar ratio was equal to (2:3) or close to (2:4), the stoichiometrically matched, network formation took place from the second condensation step, whereas three reaction steps were necessary for network formation far from stoichiometry, at G:S molar ratios equal to 2:2 and 2:5 at a G:S molar ratio of 2:1, no network formation was observed at all. Network composition also proved to be an important structural property, directly influencing the swelling and thermomechanical behavior of the elastomers. In particular, at the stoichiometrically matched G:S ratio of 2:3, corresponding to the cross-linking density maximum, the sol fraction extracted from the elastomers and the elastomer degree of swelling in aqueous media and in organic solvents presented a minimum, whereas the storage moduli of PGS elastomeric membranes in the dry state, measured within the temperature range between 35 and 140 C, exhibited a maximum. The molecular weights of all soluble network precursors were found to be below 5000 g mol-1 (gel permeation chromatography), containing but traces of ring oligomers (electron-spray ionization mass spectrometry). 1H NMR spectroscopy indicated that the precursor composition was close to that expected on the basis of the G:S feed ratio and that monomer-to-polymer conversion increased from the first to the second condensation step. © 2013 American Chemical Society. 46 3 622 630 Cited By :14

A novel bifunctional bis(hemiacetal ester) chain transfer agent (CTA), 1,2-bis[1-(4-cyano-4-methyl-1-oxo-4-(phenylcarbonothioylthio)butanoxy)ethoxy] ethane (CMPTBEE), appropriate for the reversible addition-fragmentation chain transfer (RAFT) polymerization of methacrylate monomers, was successfully synthesized and used for the preparation of a family of 10 hydrolyzable end-linked polymer (co)networks. The family comprised three methyl methacrylate (MMA) homopolymer networks with different degrees of polymerization, 100, 150, and 200, and seven end-linked amphiphilic polymer conetworks of MMA and 2-(dimethylamino)ethyl methacrylate (DMAEMA) with a constant overall degree of polymerization equal to 200 but various compositions and architectures. The agreement of the experimentally measured molecular weights with the theoretically expected ones and the low molecular weight dispersities of the linear precursors to the (co)networks indicated successful control of the polymerization. All (co)networks were characterized in terms of their sol fraction and in terms of their degree of swelling in THF. The value of the former was found in the range between 4 and 50%, whereas that of the latter was around 13%. The presence of the hemiacetal ester groups allowed the hydrolysis of the most hydrophilic, DMAEMA-rich conetworks. The resistance to hydrolysis of the other (co)networks could be attributed to the large hydrophobic blocks surrounding and protecting from hydrolysis the hemiacetal ester groups of the CTA residue in the conetworks. © 2012 American Chemical Society. 45 19 7890 7899 Cited By :22

Group transfer polymerization and sequential addition of monomer and cross-linker were employed for the preparation of two new polymer structures, one of a polymer network and the other of a star polymer. The synthesis was completed in two steps, involving the synthesis of linear methyl methacrylate (MMA) arms of degree of polymerization of 20, followed by their cross-linking using a mixture of MMA monomer and ethylene glycol dimethacrylate (EGDMA) cross-linker. In this study, the volume of the cross-linking mixture was varied systematically. Furthermore, two mixture compositions were employed, involving MMA:EGDMA molar ratios of 1:1 and 3:1, leading to two series of polymeric materials. It was found that at a given cross-linking mixture composition, a larger volume of the cross-linking mixture favored the formation of polymer networks, whereas a smaller volume favored the formation of star polymers. The linear precursors, the star polymers and the extractables from the polymer networks were characterized by gel permeation chromatography in tetrahydrofuran (THF). The absolute weight-average molecular weight, the number of arms and the hydrodynamic radii of the star polymers, as determined using static and dynamic light scattering in THF, respectively, and their average radii as determined by atomic force microscopy, increased as the volume of the cross-linking mixture increased. The gravimetrically measured degrees of swelling in THF, the network sol fraction and the percentage of branched polymer in the sol fraction decreased as the volume of the cross-linking mixture increased. © 2008 Elsevier Ltd. All rights reserved. 45 1 10 18 Cited By :10

Group transfer polymerization was employed for the preparation of six amphiphilic terpolymer networks comprising the hydrophilic, pH-responsive 2-(dime- thylamino)ethyl methacrylate (DMAEMA), the neutral hydrophilic methoxy hexa (ethylene glycol) methacrylate (HEGMA), and the hydrophobic n-butyl methacrylate (BuMA). 1,4-Bis(methoxytrimethylsiloxymethylene)cyclohexane was used as a bifunc- tional initiator, whereas ethylene glycol dimethacrylate served as the crosslinker to interconnect the linear terpolymer precursors to three-dimensional terpolymer net- work structures. Five of the terpolymer networks were model, with linear chains between crosslinks of precise length. Four of the five model networks were based on ABCBA pentablock terpolymers with theoretical structure DMAEMA5-b-BuMAn/2-b- HEGMA10-b-BuMAn/2-b-DMAEMA5 with n values equal to 5, 10, 20, and 30. The model network based on the equimolar statistical terpolymer and the nonmodel ran- domly crosslinked terpolymer network were also prepared. The molecular weights and compositions of the linear pentablock terpolymer precursors to the networks were found to be close to the theoretically expected, while the network sol fractions were found to be relatively low. The degrees of swelling of the networks in water were found to decrease with increasing the hydrophobic content, whereas those in THF exhibited the opposite trend. Small-angle neutron scattering in deuterium oxide indicated structural organization in the most hydrophobic pentablock terpolymer net- works. V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4420-4432, 2008

The recent literature on chemically cross-linked amphiphilic polymer networks is reviewed. The main subjects covered are network synthesis, characterization, modeling and applications. Special mention is made to more modern methods for amphiphilic network synthesis and in particular to those involving controlled polymerization techniques. A key question regarding synthesis is which method gives the most perfect networks. On the characterization side is the issue of microphase separation of amphiphilic networks in water and the morphologies obtained in these systems, in comparison with the morphologies of amphiphilic linear block copolymers in water. Major recent advances: The most important developments of the past year in the field of amphiphilic polymer networks involved mainly new syntheses: cross-linked stars of various star architectures, cross-linked linear chains of various architectures and compositions, poly(tetrahydrofuran)- and poly(propylene fumarate)-based networks, tricomponent networks containing silicon, and cross-linked poly(acrylic acid)-grafted Pluronics. A first crude model was also developed which shows that amphiphilic networks prefer to be mostly in the microphase separated state. Extensive and systematic experimental studies on network microphase separation are yet to be performed. © 2003 Elsevier Science Ltd. All rights reserved. 8 1-2 76 85 Cited By :144

A series of seven dynamic covalent networks based on pentaerythritol tetra(benzohydrazide) and 1,10-decanediol dibenzaldehyde were prepared in N,N-dimethylformamide (DMF). The equilibrium degree of swelling in DMF and the sol fraction displayed a minimum at or near the hydrazide-benzaldehyde stoichiometric ratio. The composition of the sol fraction changed according to the feed composition, with the dibenzaldehyde-rich preparations exhibiting extractables composed of star oligomers based on tetra(benzohydrazide) cores. Finally, network reversibility and self-healing were demonstrated in the presence of acid. © 2014 Society of Chemical Industry. 63 9 1558 1565 Cited By :10

A series of amphiphilic end-linked conetworks was synthesized by the combination of two "quasiliving" polymerization techniques, quasiliving carbocationic (QLCCP) and group transfer polymerizations (GTP). The hydrophobic monomer was polyisobutylene methacrylate synthesized by the QLCCP of isobutylene and subsequent terminal modification reactions. The hydrophilic monomer was methacrylic acid (MAA) introduced via the polymerization of 2-tetrahydropyranyl methacrylate followed by acid hydrolysis after (co)network formation. The conetwork syntheses were performed by sequential monomer/crosslinker additions under GTP conditions. All the precursors and the extractables from the conetworks were characterized by gel permeation chromatography and H-1 NMR. The resulting polymer conetworks were investigated in terms of their degree of swelling (DS) in aqueous media and in tetrahydrofuran (THF) over the whole range of ionization of the MAA units and in n-hexane for uncharged conetworks. The DSs in water increased with the degree of ionization (DI) of the MAA units and the hydrophilic content in the conetwork, whereas the DSs in THF increased with the reduction of the DI of the MAA units. The effective pK of the MAA units in the conetworks increased from 8.4 to 10.5 with decreasing MAA content. These findings can facilitate the design of similar unique conetworks with adjustable swelling behavior and composition-de pendent pK values. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4289-4301, 2009

Linear homopolymers and randomly cross-linked homopolymer networks of 2-(dimethylamino)ethyl methacrylate of various molecular weights (MWs) were synthesized by group transfer polymerization in the bulk. 1-methoxy-1-(trimethylsiloxy)-2-methyl propene was used as the initiator, while tetrabutylammonium bibenzoate served as the catalyst. Ethylene glycol dimethacrylate was the cross-linker used for the network synthesis at an 8-fold molar excess with respect to the initiator. Gel permeation chromatography in tetrahydrofuran was used to characterize the linear homopolymers in terms of their MW and molecular weight distribution (MWD). Although the experimental MWs did not match the theoretical MWs, they were reasonably close to them. The MWDs were rather broad with polydispersity indices ranging between 1.5 and 1.9. The monomer conversion was relatively high, ranging from 97% to 74% for theoretical degrees of polymerization (DPs) from 5 to 500. No polymerization was observed for an attempted DP of 1000. Networks with molar ratios of monomer to initiator (nominal DPs) from 5 to 200 were prepared, while an attempted synthesis with a nominal DP of 500 did not yield a network. The networks were characterized in terms of their degree of swelling in water and the effects of DP, pH, salt concentration and temperature were investigated. © 2002 Elsevier Science Ltd. All rights reserved. 39 3 609 616 Cited By :7

Amlodipine besylate microspheres for intranasal administration were prepared with an aim to avoid first-pass metabolism, to achieve controlled blood level profiles and to improve therapeutic efficacy. Hydroxypropyl Guar, a biodegradable polymer, was used in the preparation of microspheres by employing water in oil emulsification solvent evaporation technique. The formulation variables were drug concentration, emulsifier concentration, temperature, agitation speed and polymer concentration. All the formulations were evaluated for particle size, particle shape and surface morphology by scanning electron microscopy, percentage yield, drug entrapment efficiency, in vitro mucoadhesion test, degree of swelling and in vitro drug diffusion through sheep nasal mucosa. The microspheres obtained were free flowing, spherical and the particles ranged in size from 13.4±2.38 μm to 43.4±1.92 μm very much suitable for nasal delivery. Increasing polymer concentration resulted in increased drug entrapment efficiency and increased particle size. Amlodipine besylate was entrapped into the microspheres with an efficiency of 67.2±1.18 % to 81.8±0.64 %. The prepared microspheres showed good mucoadhesion properties, swellability and sustained the release of the drug over a period of 8 h. The data obtained were analysed by fitment into various kinetic models; it was observed that the drug release was matrix diffusion controlled and the release mechanism was found to be non-Fickian. Stability studies were carried out on selected formulations at 5±3°, 25±2°/60±5% RH and 40±2°/75±5% RH for 90 days. The drug content was observed to be within permissible limits and there were no significant deviations in the in vitro mucoadhesion and in vitro drug diffusion characteristics.