In this work, an agarose/poly(acrylamide‐co‐acrylic acid) interpenetrating network hydrogel is prepared by the photopolymerization of acrylamide, acrylic acid, and N ,N ′‐methylenebisacrylamide within agarose network at its gel state. The as‐prepared hydrogel exhibits two independent kinds of shape memory effects. The thermal‐activated shape memory behavior is attributed to the reversible coil‐helix transformation of agarose, within the permanently cross‐linked poly(acrylamide‐co‐acrylic acid) network; the light triggered shape recovery is driven by the dissociation of the complexes between carboxyl groups and Fe(III) ions, due to the photoreduction of Fe(III) to Fe(II) in the presence of citric acid. The versatile and simple strategy as presented here should be beneficial for the design of dual‐activated shape memory hydrogels and foster their use in a number of fields such as biomaterials, soft robotics, smart actuators, and sensors.
Macroporous cross‐linked organic polymers, based on styrene and divinylbenzene (PS‐DVB), are prepared as monolithic stationary phases for capillary electrochromatographic applications. The synthetic strategy, which relies on the semi‐interpenetrating polymer network (semi‐IPN) approach, is performed through UV‐initiated free radical copolymerization of the comonomers in the presence of poly(?‐caprolactone) (PCL) within the confines of fused silica capillaries. The characterization of PS‐DVB monoliths is carried out at the different stages of the synthesis using a combination of experimental techniques, thus providing information on the chemical and porous structures. All experimental results evidence the sole role of the PCL oligomer as a porogen. 相似文献
An intelligent nanocomposite hydrogel with a semi‐interpenetrating organic/inorganic network was synthesized through in situ free‐radical polymerization of NIPA in the presence of an inorganic clay and linear PAA. The resulting semi‐interpenetrating nanocomposite gels (sI‐NC gels) showed mechanical and swelling/deswelling properties greatly superior to those of other PNIPA/PAA hydrogels. The sI‐NC gels repeatedly changed their swelling behavior in response to both temperature and pH while retaining their remarkable mechanical properties. The structure and homogeneity of these networks were studied and related to the properties of sI‐NC gels and the hydrogen bonding interactions among the constituents.
Summary: The crystallization behavior and mechanical properties of composites of PLLA and FPEOF were studied using DSC, DMA and tensile strength measurements. For PLLA/FPEOF composites aged at room temperature, when PLLA was amorphous, an astonishing around 100 times increase in the fracture strain with a high modulus was observed. For PLLA/FPEOF composites aged at 90 °C, the mechanical performance of the composites was greatly decreased and the fracture strain did not show much of an increase compared with pure PLLA. A mechanism for the large changes in the mechanical properties of PLLA/FPEOF blends aged at different temperatures was proposed.
Strain‐stress curves of the PLLA/FPEO20F6 composite aged at 90 °C and room temperature. 相似文献
This paper reports a novel synthetic process to obtain poly(ethylene glycol)‐coated magnetite nanoparticles. Magnetite nanoparticles were synthesized by a chemical co‐precipitation of Fe2+ and Fe3+ ions under alkaline conditions, which were then coated with poly(ethylene glycol) diacrylate via UV‐curing in water. The nanoparticles were characterized by means of DLS, FT‐IR spectroscopy, TGA, TEM, and XPS. The magnetic properties of the magnetic nanoparticles at room temperature were also characterized by the measurement of hysteresis curves using a vibrating‐sample magnetometer.
A series of interpenetrating polymer networks (IPNs) of poly(N‐isopropylacrylamide) (PNIPA) with anionic poly(acrylic acid) (PAA) and cationic poly[[3‐(methacryloylamino)propyl]trimethylammonium chloride] (PMAPTAC) have been synthesized. The swelling behavior of the IPNs is monitored as a function of both pH and temperature. The swelling ratios of IPNs are significantly larger than those reported for pure PNIPA gels. [PNIPA‐PAA] IPNs show a continuous volume phase transition (VPT) at pHs below the pKa of PAA and at pH > pKa the IPNs show a temperature independent swelling. [PNIPA‐PMAPTAC] IPNs do not exhibit VPT at any given pH and over the range of temperatures studied. 相似文献
Summary: Novel temperature sensitive poly(N‐isopropylacrylamide‐co‐acryloyl beta‐cyclodextrin) (P(NIPA‐co‐A‐CD)) hydrogels with fast shrinking rates were prepared by radical polymerization of NIPA, A‐CD and crosslinker in a mixture of water/1,4‐dioxane as solvent. Because the mixed solvent was a poor solvent for the copolymers, phase separation occurred during the polymerization, which resulted in a heterogeneous, porous structure of the hydrogels. In contrast to the normal PNIPA hydrogel and the homo P(NIPA‐co‐A‐CD) gel prepared in water, the P(NIPA‐co‐A‐CD) hydrogels synthesized in water/1,4‐dioxane as solvent exhibited higher swelling ratios at the temperature below the lower critical solution temperature (LCST) and shrunk rapidly to equilibrium within shorter time when the temperature was increased above LCST. Increasing the acryloyl beta‐cyclodextrin content in the gels led to a slight decrease of the swelling ratio at lower temperature and had no marked influence on the shrinking kinetics. The gels prepared in water/1,4‐dioxane, at different v/v ratios of 1.0/0.2, 0.8/0.4 and 0.6/0.6, showed similar properties.
SEM photos of the heterogeneous P(NIPA‐co‐A‐CD) hydrogel prepared in water/1,4‐dioxane. 相似文献
A novel acrylamide/maleic acid copolymer [P(AM‐MA)] hydrogel nanofibrous membrane with a fiber diameter of ca. 120 nm is prepared by electrospinning an aqueous P(AM‐MA) solution with diethylene glycol as crosslinker, followed by a heat‐induced esterification crosslinking reaction at 145 °C. This hydrogel nanofiber can maintain a fiber form, but becomes distorted and merges to form many physical crosslinking points after immersion in water. The P(AM‐MA) hydrogel nanofibers are sensitive to external stimuli ionic strength and pH. Their water‐swelling ratio decreases with increasing solution ionic strength, and it shows a characteristic two‐step increase at pH = 2.5 and 8.5 in response to the increase of solution pH. The maximum water‐swelling ratios of the P(AM‐MA) hydrogel nanofibers are 18.1 and 22.5 g · g?1 in a solution of 0.05 mol · dm?3 ionic strength and in an aqueous solution of pH 11, respectively.
In the present contribution, we synthesized linear coordination polymers based on oligo(ethylene glycol)s as well as poly(ethylene glycol)s and terpyridine ruthenium(II) complexes. The reaction conditions, e.g., solvent, concentration, were varied to obtain well‐soluble, high molecular weight polymers. The resulting compounds were characterized by UV‐vis and NMR spectroscopy. The viscosity of the materials was also investigated with and without salt addition. Finally, the polymers were characterized with DSC and AFM. AFM revealed a lamellar morphology.
A series of poly(methyl methacrylate‐co‐methacrylic acid) (PMMA‐co‐MAA) random copolymers ranging in MAA content from 0–15 mol% is synthesized and blended with poly(vinylidene fluoride) (PVDF). Using infrared spectroscopy, it is observed that the absorption bands attributed to hydrogen‐bonded carbonyl groups increase in intensity as the amount of MAA in the copolymer increases. In DSC analysis, the crystallization temperature of the PVDF in the blend initially decreases by ca. 12 °C with MAA contents ranging from 0 to 5.5 mol%; however, a PVDF blend with a 15 mol% MAA copolymer has a crystallization temperature that is only ca. 3 °C below that of pure PVDF. Similarly, spherulitic growth rate analysis initially shows a decrease in radial growth rate for PVDF in blends with PMMA‐co‐MAA copolymers containing less than 5.5 mol% MAA. At higher MAA copolymer contents, the spherulitic growth rate approaches that of pure PVDF. It is concluded that the presence of the MAA comonomer in the PMMA‐co‐MAA copolymer initially (<5.5 mol% MAA) increases the intermolecular interactions between the copolymer and the PVDF. However, as the MAA content of the copolymer rises above 5.5 mol%, intramolecular hydrogen bonding interactions within the PMMA‐co‐MAA copolymer cause the copolymer to be less compatible with PVDF.
Clickable poly(ethylene glycol) (PEG) derivatives are used with two sequential aqueous two‐phase systems to produce microsphere‐based scaffolds for cell encapsulation. In the first step, sodium sulfate causes phase separation of the clickable PEG precursors and is followed by rapid geleation to form microspheres in the absence of organic solvent or surfactant. The microspheres are washed and then deswollen in dextran solutions in the presence of cells, producing tightly packed scaffolds that can be easily handled while also maintaining porosity. Endothelial cells included during microsphere scaffold formation show high viability. The clickable PEG‐microsphere‐based cell scaffolds open up new avenues for manipulating scaffold architecture as compared with simple bulk hydrogels.
A new thermosensitive poly(N‐propionyl‐aspartic acid/ethylene glycol) (PPAE) with no cytotoxicity and an upper critical solution temperature (UCST) is synthesized by polycondensation of l ‐aspartic acid and ethylene glycol. The chemical structures of the monomer and polymer are confirmed by FTIR and 1H NMR spectroscopy, and by elemental analysis measurements. Turbidimetric measurements indicate that PPAE shows a reversible UCST phase transition at 1.5–37.6 °C in pure water or an alcohol/water mixture. The UCST can be facilely tuned via changing the content of alcohol in water or the normal saline. Moreover, the survival rate of HeLa cells to PPAE is close to 100% within 48 h, demonstrating no cytotoxicity. Such aspartic acid‐based polymers with tunable thermosensitivity could be useful in the biomedical field.
Chemically crosslinked hydrogels are prepared at remarkably low macromonomer concentrations from 8‐arm poly(ethylene glycol)‐poly(L ‐lactide) star block copolymers bearing acrylate end groups (PEG‐(PLLAn)8‐AC, n = 4 or 12) and multifunctional PEG thiols (PEG‐(SH)n, n = 2, 4, or 8) through a Michael‐type addition reaction. Hydrogels are obtained within 1 min after mixing PEG‐(PLLA4)8 ‐AC and PEG‐(SH)8 in phosphate buffered saline, quickly reaching a high storage modulus of 17 kPa. Lysozyme and albumin are released for 4 weeks from PEG‐(PLLA12)8‐AC/PEG‐(SH)8 hydrogels. Lysozyme release from PEG‐(PLLA12)8‐AC/PEG‐(SH)2 and PEG‐(PLLA12)8‐AC/PEG‐(SH)4 hydrogels is significantly faster with complete release in 3 and 12 d, respectively, as a result of a combination of degradation and diffusion. 相似文献
Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (T cp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between T cp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications.
Acrylic acid copolymers bearing radically polymerizable methacrylic and itaconic moieties are synthesized. Starting from copolymers of tBA and APVE, prepared at different ratios, methacrylic or itaconic amides are obtained via polymer‐analogous reaction. After acidic elimination of isobutylene, polymers with free carbon acids and staggered reactivity can be prepared. Varying amounts of attached acrylamide moieties allow the adjustment of network densities. Rheological properties in HEMA/water matrices during curing are evaluated. 相似文献
The amphiphilic triblock copolymer PLA‐b‐PLL‐b‐MPEG is prepared in three steps through acylation coupling between the terminal amino groups of PLA‐b‐PZLL‐NH2 and carboxyl‐terminal MPEG, followed by the deprotection of amines. The block copolymers are characterized via FT‐IR, 1H NMR, DSC, GPC, and TEM. TEM analysis shows that the triblock polymers can form polymeric micelles in aqueous solution with a homogeneous spherical morphology. The cytotoxicity assay indicates that the final triblock polymer micelles after deprotection show low cytotoxicity against Bel7402 human hepatoma cells. MPEG and PLL were introduced into the main chain of PLA affording a kind of ideal bioabsorbable polymer materials, which is expected to be useful in drug and gene delivery.
The use of responsive thin hydrogel films as the active matrix in sensor applications requires detailed knowledge of their structural and dynamical properties and their responsiveness to external conditions. Here, the structure and dynamics in photo‐crosslinked, surface‐attached films (≈1 μm dry thickness) of a poly(N‐isopropylacrylamide) (PNIPAAm)‐based terpolymer (containing 5% methacrylic acid and 1% benzophenone methacrylate comonomers) at different temperatures and salt (NaCl) contents are reported. The swelling is monitored by surface plasmon resonance/optical waveguide spectroscopy (SPR/OWS), and the hydrogel dynamics are studied by micro‐photon correlation spectroscopy. In addition to the expected volume phase transition above a critical temperature of ca. 32–35 °C and at NaCl concentrations above 1 m , SPR/OWS reveals subtle thickness variations at lower salt concentrations. The fast cooperative diffusion of the polymer network and a slow mode for the relaxation of the thermal concentration fluctuations in the grafted hydrogel layer exhibit a non‐monotonic dependence on the salinity and a strong slowdown with temperature near the collapse transition. These dynamics respond sensitively and distinctly to structural changes induced by increasing temperature or added monovalent salt in comparison to the only subtle changes of the polymer fraction.
Summary: Hydrogels of NIPA and MBDA were synthesized by free‐radical crosslinking copolymerization with different monomer ratios and with two concentrations of the crosslinking agent. The aim of this work was to study the swelling behavior of these gels that are both temperature and pH sensitive. PNIPA hydrogels are typical examples of thermo‐shrinking hydrogels with a LCST, TC, around 31–34 °C. MBDA is a weakly ionizable monomer which imparts a pH sensitiveness to the copolymer hydrogels. The pH influence on the swelling behavior of the studied hydrogels was analyzed using deionized water and aqueous HCl and NaOH as swelling media. According to the results found in deionized water, the swelling processes of P(NIPA‐MBDA) hydrogels follow second‐order kinetics at 22 and 37 °C. The equilibrium water content, W∞, and the rate constant, K, increased at greater concentrations of MBDA and decreased as the crosslinking agent concentration increased. As the MBDA content in the hydrogel increased, the collapsing of the hydrogels at higher temperatures than the LCST became of less importance. The degree of swelling of pure PNIPA hydrogels was not influenced by the pH of the swelling medium. However, this influence increased as the MBDA content increased. This was due to the fact that at low pH most of the MBDA units are in the protonated (neutral) form and at high pH in the ionized one.
Swelling isotherms of hydrogels with different copolymer compositions and with 1.5 wt.‐% of BIS at 22 °C in deionized water. 相似文献
New hydrophilic networks combining poly(ethylene glycol) (PEG) and β‐cyclodextrin (β‐CD) have been prepared. Both components are linked by reacting PEG chains previously end‐capped with isocyanate groups and β‐CD, forming urethane links. Networks of molar compositions (β‐CD/PEG) ranging from 1/4 to 1/14, and with four different molar masses (400, 600, 900, and 1 350 g · mol?1) of the end‐capped PEG precursor have been synthesized. The networks have good thermal stability and low glass transition temperatures. Crystallinity has only been detected for the two higher molar mass PEG precursors. The swelling properties of these hydrogels depend on the chain lengths of the PEG precursor and also on the temperatures.
The preparation and structural organization of a new bioinspired nanomaterial are investigated. A hybrid conjugate is obtained by end‐linking a linear octapeptide with regular alternating enantiomeric sequence to poly(ethylene glycol). This conjugate is able to self‐assemble, forming well‐defined nanorods having core/shell morphology with an internal peptide single channel that has, for the first time, been clearly visualized by transmission electron microscopy (TEM) images. It is remarkable that well‐defined cylindrical nanoparticles can be formed starting from a linear oligopeptide, the synthesis of which is significantly easier than that of the homologous cycles. In addition, the synthetic strategy and the structure of the conjugate ensure a controlled and regular pegylation of the aggregates and high density PEG blocks in the corona, making the nanoparticles more resistant to phagocytosis and able to prevent biofouling. Such features, along with biocompatibility and stability, make these nanoparticles promising candidates for drug delivery.
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