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Isopropylacrylamide
Selected AbstractsPolymerization of N -isopropylacrylamide in the presence of poly(acrylic acid) and poly(methacrylic acid) containing ,-unsaturated end-groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2007Ronan Mchale Poly(N -Isopropylacrylamide, NIPAM) propagating radicals add to acrylic acid (AA) macromonomer and methacrylic acid polymer containing unsaturated ,-end-group to respectively give novel graft copolymer (represented as , (AA) and , (NIPAM) units) and addition fragmentation chain transfer (AFCT). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley. com.] [source] Thermal Sensitivity of tert -Butyloxycarbonylmethyl-Modified Polyquats in Condensed Phase and Solubility Properties of Copolymers with N -IsopropylacrylamideMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 15 2010Nina Gonsior Abstract The synthesis of the easily decomposable ionic monomer 2- tert -butoxy- N -[2-(methacryloyl-oxy)ethyl]- N,N -dimethyl-2-oxoethanammonium chloride (3) via thermally induced syn-elimination of a tert -butyl ester group was realized simply by mixing N,N -dimethylaminoethyl methacrylate (1) and tert -butyl chloroacetate (2) at ambient temperature without solvent. The obtained salt was polymerized via free radical polymerization. The decomposition and foaming via iso -butene formation takes place by heating up to about 160,°C. IR, DSC, TGA, and GC/MS measurements were performed to follow this pyrolysis reaction. Furthermore, the copolymerization of 3 with N -isopropylacrylamid (NiPAAm, 5) was carried out with different monomer ratios. Molar mass distributions were measured using an asymmetrical flow field-flow fractionation (aFFFF) system. The obtained copolymers 6,10 exhibit lower critical solution temperature (LCST) behaviour in water with cloud points at different temperatures depending on the monomer ratio. [source] In Situ Characterization of Thermo-Responsive Poly(N -Isopropylacrylamide) Films with Sum-Frequency Generation SpectroscopyCHEMPHYSCHEM, Issue 7 2010Volker Kurz Abstract The thermo-responsive behaviour of thiol modified poly(N -isopropylacrylamide) (pNIPAM) films immobilized on gold are probed by in situ broadband sum-frequency generation (SFG) spectroscopy. The pNIPAM films were prepared by atom transfer radical polymerization (ATRP) using a nitro-biphenyl-thiol (NBT)-SAM on a polycrystalline gold surface as a substrate. Additionally, Raman and infrared reflection absorption spectroscopy (IRRAS) are applied to spin-coated pNIPAM films. Molecular groups involved in the reorientation and disordering of the polymer chains during the LCST (lower critical solution temperature) transition of pNIPAM are identified. The characteristic vibrations of the CH3 groups show a gradual reorientation of the isopropyl groups within the pNIPAM film and instantaneous reorientation of the outermost CH3 groups around 32,°C. [source] Electrochemically Induced Formation of Surface-Attached Temperature-Responsive Hydrogels.ELECTROANALYSIS, Issue 9 2010Amperometric Glucose Sensors with Tunable Sensor Characteristics Abstract Employing thermally responsive hydrogels, the design of an amperometric glucose sensor is proposed. The properties of the biosensor can be modulated upon changing the temperature. Homo- and copolymers of N -isopropylacrylamide (NIPAm) and oligo(ethylene glycol) methacrylate (OEGMA) were prepared by electrochemically induced polymerization thus yielding surface-attached hydrogels. The growth of the films as well as the change in the film thickness in dependence from the temperature were investigated by means of an electrochemical quartz crystal microbalance (EQCM). The layer thickness in the dry state ranged from 20 to 120,nm. The lower critical solution temperature (LCST) of the hydrogel increases with increasing content of the more hydrophilic OEGMA. Hence, the swelling in aqueous electrolyte is composition dependent and can be adjusted by selecting a specific NIPAm to OEGMA ratio. All homo- and copolymer films showed good biocompatibility and no fouling could be observed during exposing the surfaces to human serum albumin. For amperometric glucose detection, glucose oxidase was entrapped in the films during electrochemically-induced polymerization. Both the apparent Michaelis constant (K and the apparent maximum current (i as determined by amperometry could be adjusted both by the film composition as well as the operation temperature. [source] Preparation and characterization of temperature-responsive capillary electrochromatographic column using poly(N -isopropylacrylamide)ELECTROPHORESIS, Issue 4 2009Rongji Dai Abstract Poly(N -isopropylacrylamide) is a temperature-responsive polymer, which is hydrophilic at low temperature but hydrophobic at high temperature. Using this characteristic, the polymer was bonded to the inner surface of fused-silica capillary to prepare a temperature-responsive column to study the separation behavior in electrochromatography. [source] Competitive immunoassay by capillary electrophoresis with laser-induced fluorescence for the trace detection of chloramphenicol in animal-derived foodsELECTROPHORESIS, Issue 16 2008Can Zhang Abstract A competitive immunoassay using CE with an LIF detector was developed for the detection of chloramphenicol (CAP). The method was based on the competitive reactions between fluorescently labeled CAP hapten and free CAP, with a limited amount of anti-CAP antibody. The poly(N -isopropylacrylamide) (pNIPA) hydrogel was added in the separation buffer as a dynamic modifier to reduce adsorption and enhance reproducibility. The linear range and LOD for CAP were 0.008,5,,g/L and 0.0016,,g/L, respectively. An ELISA using the same immuno-reagents was also developed for the analysis of CAP, with an LOD of 0.03,,g/L. The sensitivity of this CE immunoassay (CEIA)-LIF was almost 20 times greater than that of the ELISA. Using CEIA-LIF, equilibrium was reached in 15,min and the analytical results were obtained within 5,min by CE separation. Sample preparation for CEIA-LIF was not time-consuming and the matrix effect was easy to remove. An LOD of 0.1,,g/kg CAP in food matrices was easily achieved. This method is thus proposed as a fast and sensitive means of detecting trace amounts of CAP residues in animal-derived foods. [source] Temperature-Responsive Substrates: Adhesion and Mechanical Properties of PNIPAM Microgel Films and Their Potential Use as Switchable Cell Culture Substrates (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Mater. Abstract Thermoresponsive poly(N -isopropylacrylamide) (PNIPAM) microgel films are shown to allow controlled detachment of adsorbed cells via temperature stimuli. Cell response occurs on the timescale of several minutes, is reversible, and allows for harvesting of cells in a mild fashion. The fact that microgels are attached non-covalently allows using them on a broad variety of (charged) surfaces and is a major advantage as compared to approaches relying on covalent attachment of active films. In the following, the microgels' physico-chemical parameters in the adsorbed state and their changes upon temperature variation are studied in order to gain a deeper understanding of the involved phenomena. By means of atomic force microscopy (AFM), the water content, mechanical properties, and adhesion forces of the microgel films are studied as a function of temperature. The analysis shows that these properties change drastically when crossing the critical temperature of the polymer film, which is the basis of the fast cell response upon temperature changes. Furthermore, nanoscale mechanical analysis shows that the films posses a nanoscopic gradient in mechanical properties. [source] Adhesion and Mechanical Properties of PNIPAM Microgel Films and Their Potential Use as Switchable Cell Culture SubstratesADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Stephan Schmidt Abstract Thermoresponsive poly(N -isopropylacrylamide) (PNIPAM) microgel films are shown to allow controlled detachment of adsorbed cells via temperature stimuli. Cell response occurs on the timescale of several minutes, is reversible, and allows for harvesting of cells in a mild fashion. The fact that microgels are attached non-covalently allows using them on a broad variety of (charged) surfaces and is a major advantage as compared to approaches relying on covalent attachment of active films. In the following, the microgels' physico-chemical parameters in the adsorbed state and their changes upon temperature variation are studied in order to gain a deeper understanding of the involved phenomena. By means of atomic force microscopy (AFM), the water content, mechanical properties, and adhesion forces of the microgel films are studied as a function of temperature. The analysis shows that these properties change drastically when crossing the critical temperature of the polymer film, which is the basis of the fast cell response upon temperature changes. Furthermore, nanoscale mechanical analysis shows that the films posses a nanoscopic gradient in mechanical properties. [source] Preparation and Characterization of a pH- and Thermally Responsive Poly(N -isopropylacrylamide- co -acrylic acid)/Porous SiO2 HybridADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Loren A. Perelman Abstract A multifunctional nanohybrid composed of a pH- and thermoresponsive hydrogel, poly(N -isopropylacrylamide- co -acrylic acid) [poly(NIPAM- co -AAc)], is synthesized in situ within the mesopores of an oxidized porous Si template. The hybrid is characterized by electron microscopy and by thin film optical interference spectroscopy. The optical reflectivity spectrum of the hybrid displays Fabry,Pérot fringes characteristic of thin film optical interference, enabling direct, real-time observation of the pH-induced swelling, and volume phase transitions associated with the confined poly(NIPAM- co -AAc) hydrogel. The optical response correlates to the percentage of AAc contained within the hydrogel, with a maximum change observed for samples containing 20% AAc. The swelling kinetics of the hydrogel are significantly altered due to the nanoscale confinement, displaying a more rapid response to pH or heating stimuli relative to bulk polymer films. The inclusion of AAc dramatically alters the thermoresponsiveness of the hybrid at pH 7, effectively eliminating the lower critical solution temperature (LCST). The observed changes in the optical reflectivity spectrum are interpreted in terms of changes in the dielectric composition and morphology of the hybrids. [source] Au@pNIPAM Thermosensitive Nanostructures: Control over Shell Cross-linking, Overall Dimensions, and Core GrowthADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Rafael Contreras-Cáceres Abstract Thermoresponsive nanocomposites comprising a gold nanoparticle core and a poly(N -isopropylacrylamide) (pNIPAM) shell are synthesized by grafting the gold nanoparticle surface with polystyrene, which allows the coating of an inorganic core with an organic shell. Through careful control of the experimental conditions, the pNIPAM shell cross-linking density can be varied, and in turn its porosity and stiffness, as well as shell thickness from a few to a few hundred nanometers is tuned. The characterization of these core,shell systems is carried out by photon-correlation spectroscopy, transmission electron microscopy, and atomic force microscopy. Additionally, the porous pNIPAM shells are found to modulate the catalytic activity, which is demonstrated through the seeded growth of gold cores, either retaining the initial spherical shape or developing a branched morphology. The nanocomposites also present thermally modulated optical properties because of temperature-induced local changes of the refractive index surrounding the gold cores. [source] Temperature Responsive Solution Partition of Organic,Inorganic Hybrid Poly(N -isopropylacrylamide)-Coated Mesoporous Silica Nanospheres,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2008Po-Wen Chung Abstract A series of poly(N -isopropylacrylamide)-coated mesoporous silica nanoparticle materials (PNiPAm-MSNs) has been synthesized by a surface-initiated living radical polymerization with a reversible addition,fragmentation chain transfer (RAFT) reaction. The structure and the degree of polymerization of the PNiPAm-MSNs has been characterized by a variety of techniques, including nitrogen sorption analysis, 29Si and 13C solid-state NMR spectroscopy, transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The thermally induced changes of the surface properties of these polymer-coated core,shell nanoparticles have been determined by examining their partition activities in a biphasic solution (water/toluene) at different temperatures. [source] A Thermoresponsive Membrane for Chiral Resolution,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2008Mei Yang Abstract A novel thermoresponsive membrane for chiral resolution with high performance has been developed. The membrane exhibits chiral selectivity based on molecular recognition of beta-cyclodextrin (, -CD) and thermosensitivity based on the phase transition of poly(N -isopropylacrylamide) (PNIPAM). Linear PNIPAM chains were grafted onto porous nylon-6 membrane substrates by using a plasma-graft pore-filling polymerization method; the chains thus acted as microenvironmental adjustors for , -CD molecules. , -CD moieties were introduced into the linear PNIPAM chains by a chemical grafting polymerization method and acted as chiral selectors. The phase transition of grafted PNIPAM chains affects the microenvironment of , -CD molecules and, thus, the association between , -CD and guest molecules. The chiral selectivity of the prepared thermoresponsive membranes in chiral resolution operated at temperature below the lower critical solution temperature (LCST) of PNIPAM is higher than that of membranes with no thermosensitivity. Furthermore, the decomplexation ratio of enantiomer-loaded thermoresponsive membranes in decomplexation at temperatures above the LCST is much higher than that of membranes with no thermosensitivity. Thus, by simply changing the operation temperature, high, selective chiral resolution and efficient membrane regeneration are achieved. The proposed membrane provides a new and efficient way to solve the difficult decomplexation problem of chiral solid membranes, which is highly attractive for chiral resolution. [source] Thermosensitive Nanostructures Comprising Gold Nanoparticles Grafted with Block Copolymers,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007D. Li Abstract Binary thermosensitive nanocomposites are fabricated by grafting block copolymers of poly(N -isopropylacrylamide) and poly(methoxy-oligo(ethylene glycol) methacrylate) onto gold nanoparticles through consecutive, surface-initiated, atom-transfer radical polymerization (ATRP). These Au@copolymer nanocomposites display a well-defined core/shell nanostructure and have two thermosensitive points near 33 and 55,°C in an aqueous suspension corresponding to the thermally induced conformational transition of inner homopolymer segments and outer oligo(ethylene glycol)-containing copolymer layer, respectively. Silver nanoparticles trapped within Au@copolymer nanocomposites with weakly crosslinked shells display thermally modulated catalytic activity as heterogeneous catalysts because of the thermosensitive collapse of the polymer layers. [source] Thermally Responsive Biomineralization on Biodegradable Substrates,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007J. Shi Abstract Biomineralization offers an elegant example of how nature can design complex, hierarchical, and structurally/morphologically controllable materials. In this work, the surface of bioactive substrates prepared from poly(L -lactic acid) and reinforced with Bioglass are modified by the graft polymerization of poly(N -isopropylacrylamide), (PNIPAAm) after plasma activation. It is found that such treatment, together with temperature, could trigger the formation of apatite on the biodegradable substrate upon immersion in simulated body fluid above the PNIPAAm lower critical solution temperature (LCST); in contrast, no apatite is formed at room temperature. A control experiment on a material that is not subjected to surface treatment does not show any evidence of mineral deposition at the two analyzed temperatures. This "smart" biomineralization concept is combined with patterning methodologies to control the microstructure of the surface onto which PNIPAAm is grafted. In this case, the apatite is formed at 37,°C in the modified regions. We suggest that this concept could be extended in the biomimetic production of other minerals, where it would be triggered by another kind of stimulus (e.g., pH or ionic strength) in substrates with more complex geometries. [source] Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2007E. Segal Abstract A thermoresponsive hydrogel, poly(N -isopropylacrylamide) (poly(NIPAM)), is synthesized in,situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO2 host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry,Pérot fringes characteristic of thin film interference, enabling direct, real-time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature-dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO2 template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite. [source] Heparinized Magnetic Nanoparticles: In-Vitro Assessment for Biomedical Applications,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2006C. Wuang Abstract Superparamagnetic magnetite nanoparticles are of great interest owing to their numerous existing and potential biomedical applications. In this study, superparamagnetic magnetite nanoparticles with average diameters of 6,8,nm have been prepared and surface-functionalized with poly(N -isopropylacrylamide) (poly(NIPAAM)) via a surface-initiated atom-transfer radical polymerization, followed by immobilization of heparin. The success of the various surface-functionalization steps has been ascertained using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The rate of internalization of the as-synthesized and surface-functionalized magnetite nanoparticles by mouse macrophage cells has been investigated. The nanoparticle internalization into the macrophages has been visualized using optical microscopy and quantified by inductively coupled plasma spectroscopy. The effectiveness of the heparinized nanoparticles in preventing thrombosis has been determined using the plasma recalcification time. The results indicate that the above-mentioned surface modifications of the magnetite nanoparticles are effective in delaying phagocytosis and preventing blood clotting in vitro. Such properties can be expected to enable their use in biomedical applications. [source] A Novel Route to Thermosensitive Polymeric Core,Shell Aggregates and Hollow Spheres in Aqueous Media,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2005Y. Zhang Abstract Poly(,-caprolactone)/poly(N -isopropylacrylamide) (PCL/PNIPAM) core,shell particles are obtained by localizing the polymerization of NIPAM and crosslinker methylene bisacrylamide around the surface of PCL nanoparticles. The resultant particles are converted to hollow PNIPAM spheres by simply degrading the PCL core with an enzyme. The hollow spheres are thermosensitive and display a reversible swelling and de-swelling at ,,32,°C. [source] Aligned Cell Sheets Grown on Thermo-Responsive Substrates with Microcontact Printed Protein PatternsADVANCED MATERIALS, Issue 21 2009Corin Williams The thermo-responsive polymer poly(N -isopropylacrylamide) is microcontact printed with fibronectin lanes. Cells seeded onto these substrates form globally aligned tissue sheets that can be harvested by lowering the temperature. [source] Temperature responsive pore-filled membranes based on a BSA/poly(N -isopropylacrylamide) hydrogelADVANCES IN POLYMER TECHNOLOGY, Issue 1 2008R. Zhang Abstract A temperature-sensitive hydrogel based on a copolymer of BSA and poly(N -isopropylacrylamide) (PNIPAAm) has been synthesized using carbodiimide chemistry. Fourier transform infrared spectroscopy confirmed primary complex formation between carbodiimide-activated carboxylic acids on the protein with protein amino groups. As a result of temperature-induced conformational changes in PNIPAAm grafted onto the protein backbone, these protein hydrogels show significant morphological changes in response to temperature. The structural changes of the gels in response to temperature were assessed using scanning electron microscopy, and the effect of temperature on their balance of hydrophobicity was found using turbidity measurements. Composite pore-filled membranes formed by impregnating glass fiber filters with the polymer mixture prior to gelation were used to determine permeability changes in response to temperature using both low (riboflavin) and intermediate (lysozyme) molecular weight diffusates. Clear correlation was found between changes in morphology, turbidity, and gel permeability as the gel temperature was increased from 24,37°C. In the case of permeability studies, significant transport of lysozyme only occurred at temperatures above the lower transition temperature of the hydrogel, suggesting the gel was acting as a mechanical "valve" to control flux. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 27:27,34, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20113 [source] Synthesis and characterization of temperature-sensitive block copolymers from poly(N -isopropylacrylamide) and 4-methyl-,-caprolactone or 4-phenyl-,-caprolactoneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Ren-Shen Lee Abstract This study synthesizes thermally sensitive block copolymers poly(N -isopropylacrylamide)- b -poly(4-methyl-,-caprolactone) (PNIPA- b -PMCL) and poly(N -isopropylacrylamide)- b -poly(4-phenyl-,-caprolactone) (PNIPA- b -PBCL) by ring-opening polymerization of 4-methyl-,-caprolactone (MCL) or 4-phenyl-,-caprolactone (BCL) initiated from hydroxy-terminated poly(N -isopropylacrylamide) (PNIPA) as the macroinitiator in the presence of SnOct2 as the catalyst. This research prepares a PNIPA bearing a single terminal hydroxyl group by telomerization using 2-hydroxyethanethiol (ME) as a chain-transfer agent. These copolymers are characterized by differential scanning calorimetry (DSC), 1H-NMR, FTIR, and gel permeation chromatography (GPC). The thermal properties (Tg) of diblock copolymers depend on polymer compositions. Incorporating larger amount of MCL or BCL into the macromolecular backbone decreases Tg. Their solutions show transparent below a lower critical solution temperature (LCST) and opaque above the LCST. LCST values for the PNIPA- b -PMCL aqueous solution were observed to shift to lower temperature than that for PNIPA homopolymers. This work investigates their micellar characteristics in the aqueous phase by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 0.29,2.74 mg L,1, depending on polymer compositions, which dramatically affect micelle shape. Drug entrapment efficiency and drug loading content of micelles depend on block polymer compositions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Lower critical solution temperature determination of smart, thermosensitive N -isopropylacrylamide- alt -2-hydroxyethyl methacrylate copolymers: Kinetics and physical propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Mohammad M. Fares Abstract The lower critical solution temperatures (LCSTs) were verified and determined for different molar feed ratios of N -isopropylacrylamide (NIPAAm) and 2-hydroxyethyl methacrylate (HEMA) monomers with ultraviolet spectroscopy and differential scanning calorimetry techniques. Increases in the NIPAAm monomer content played a crucial role in the LCST, which increased up to 36.7°C at 50 mol %. However, a further increase in the NIPAAm monomer content steadily reduced the LCST, which decreased to 33°C at 100 mol % NIPAAm [i.e., pure poly(N -isopropylacrylamide)]. The rate of copolymerization, assessed by the conventional conversion (%),time method, and the apparent activation energies were determined. The reactivity ratios of the monomers, determined by the Kelen,Tudos and Fineman,Ross techniques, together with the results of an equation, showed that the copolymer which formed was an alternating copolymer. The Q,e values for the NIPAAm monomer were determined. The equation showed the linear Arrhenius behavior of ln(r1r2) versus the reciprocal of the temperature (where r1 and r2 are the reactivity ratios of NIPAAm and HEMA, respectively): the activation energy difference [i.e., (E12 + E21) , (E11 + E22), where E12, E21, E11, and E22 are various activation energies] was found to be ,109 kJ/mol. The copolymers were characterized with 1H-NMR, 13C-NMR, Fourier transform infrared, ultraviolet,visible, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy techniques. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Morphology and photophysical properties of a thermally responsive fluorescent material based on a rod-coil tri-block copolymerJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Zhun Ma Abstract A thermally responsive rod-coil poly[poly (N -isopropylacrylamide)- b -polyfluorene- b -poly(N -isopropylacrylamide)] triblock copolymer has been successfully synthesized by atom transfer radical polymerization from an end-functionalized macroinitiator. The thermochromic behavior and relevant morphology of this polymer were investigated by UV-vis spectra, DLS, and AFM, respectively, at various temperatures. A thermally responsive fluorescent material was achieved facilely by combining the optically active polyfluorene with temperature-responsive poly(N -isopropylacrylamide). All the measurements demonstrated that in the region of 25,45°C, the polymer underwent a phase transition and the corresponding change in optical properties in its water solution. However, the polymer did not show completely reversible behavior upon heating and cooling. On the basis of the comparison with two other thermally responsive conjugated polymers in literatures, a tentative mechanism has been proposed that ,,, interaction induced rigid segments to remain chain conformation and packing styles as in collapsed state. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Release behavior of freeze-dried alginate beads containing poly(N -isopropylacrylamide) copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Jae-Hyung Choi Abstract Beads composed of alginate, poly(N -isopropylacrylamide) (PNIPAM), the copolymers of N -isopropylacrylamide and methacrylic acid (P(NIPAM- co -MAA)), and the copolymers of N -isopropylacrylamide, methacrylic acid, and octadecyl acrylate (P(NIPAM- co -MAA- co -ODA)), were prepared by dropping the polymer solutions into CaCl2 solution. The beads were freeze-dried and the release of blue dextran entrapped in the beads was observed in distilled water with time and pH. The degree of release was in the order of alginate bead < alginate/PNIPAM bead , alginate/P(NIPAM- co -MAA) bead < alginate/P(NIPAM- co -MAA- co -ODA) bead. On the other hand, swelling ratios reached steady state within 20 min, and the values were 200,800 depending on the bead composition. The degree of swelling showed the same order as that of release. Among the beads, only alginate/P(NIPAM- co -MAA- co -ODA) bead exhibited pH-dependent release. At acidic condition, inter- and intraelectrostatic repulsion is weak and P(NIPAM- co -MAA- co -ODA) could readily be assembled into an aggregate due to the prevailing hydrophobic interaction of ODA. Thus, it could block the pore of bead matrix, leading to a suppressed release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Grafting of poly(N -isopropylacrylamide) onto nylon and polystyrene surfaces by atmospheric plasma treatment followed with free radical graft copolymerizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Xiaoling Wang Abstract Stimuli-responsive polymer materials (SRPs) have potential uses in drug delivery, tissue engineering, bioreactors, and cell-surface adhesion control. Temperature-responsive surfaces were fabricated by grafting poly(N -isopropylacrylamide) (PNIPAM) onto nylon and polystyrene surfaces via a new procedure, i.e., He atmospheric plasma treatment followed by free radical graft copolymerization. The atmospheric plasma exhibits the activation capability to initiate graft copolymerization. The procedure is suitable for integration into a continuous manufacturing process. To reduce homopolymerization and enhance graft yield, Mohr's salt was added. The graft of PNIPAM was confirmed by Fourier transform infrared spectroscopy and atomic force microscopy. Dramatic water contact angle increase was found for PNIPAM-grafted polymers at about 32°C, indicating the temperature sensitivity of the grafted surface, i.e., the change of surface from hydrophilic to hydrophobic when temperature increases above the lower critical solution temperature (LCST). The addition of Mohr's salt enhances the grafting reaction and the magnitude of temperature sensitivity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3614,3621, 2007 [source] Preparation and optical properties of an all-polymer light modulator using colored N -isopropylacrylamide gel particles in a gel-in-gel systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Hiroaki Tsutsui Abstract 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 [source] Synthesis and characterization of injectable bioadhesive hydrogels for nucleus pulposus replacement and repair of the damaged intervertebral discJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2010J. Vernengo Abstract Bioadhesive polymers are natural or synthetic materials that can be used for soft tissue repair. The aim of this investigation was to develop an injectable, bioadhesive hydrogel with the potential to serve as a synthetic replacement for the nucleus pulposus of the intervertebral disc or as an annulus closure material. Branched copolymers of poly(N -isopropylacrylamide) (PNIPAAm) and poly(ethylene glycol) (PEG) were blended with poly(ethylene imine) (PEI). This three component injectable system can form a precipitated gel at physiological temperature due to the phase transition of PNIPAAm. The injection of glutaraldehyde into the gel core will adhere the implant to the surrounding tissues. 1H NMR results indicated the successful physical incorporation of PEI into the PNIPAAm-PEG network by blending. In addition, the covalent crosslinking between the amine functionalities on the PEI and the aldehyde functionalities on the glutaraldehyde was verified using FTIR difference spectroscopy. Mechanical characterization of these blends showed a significant increase (p < 0.05) in compressive modulus following glutaraldehyde injection. The in vitro bioadhesive force studies with porcine skin showed a significant increase (p < 0.05) in the mean maximum force of detachment for PNIPAAm-PEG/PEI gels when glutaraldehyde was injected into the gel core. The results of this study indicate that the reactivity between amines and aldehyde functionalities can be exploited to impart bioadhesive properties to PNIPAAm-PEG/PEI copolymers. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Characterization of the physicochemical, antimicrobial, and drug release properties of thermoresponsive hydrogel copolymers designed for medical device applicationsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008David S. Jones Abstract In this study, a series of hydrogels was synthesized by free radical polymerization, namely poly(2-(hydroxyethyl)methacrylate) (pHEMA), poly(4-(hydroxybutyl)methacrylate) (pHBMA), poly(6-(hydroxyhexyl)methacrylate) (pHHMA), and copolymers composed of N -isopropylacrylamide (NIPAA), methacrylic acid (MA), NIPAA, and the above monomers. The surface, mechanical, and swelling properties (at 20 and 37°C, pH 6) of the polymers were determined using dynamic contact angle analysis, tensile analysis, and thermogravimetry, respectively. The Tg and lower critical solution temperatures (LCST) were determined using modulated DSC and oscillatory rheometry, respectively. Drug loading of the hydrogels with chlorhexidine diacetate was performed by immersion in a drug solution at 20°C ( Flow characteristics of thermo-responsive microspheres in microchannel during the phase transitionAICHE JOURNAL, Issue 6 2009Ming-Yu Zhou Abstract To probe into the flow and aggregation behaviors of thermo-responsive microspheres in microchannel during the phase transition, the flow characteristics of monodisperse poly(n -isopropylacrylamide) (PNIPAM) microspheres in microchannel with local heating are investigated systematically. When the fluid temperature in the microchannel increases across the lower critical solution temperature (LCST), the PNIPAM microspheres finish the phase transition within 10 s and are easily get aggregated during the phase transition. The diameter ratio of microsphere to microchannel, number of microspheres, initial distance between microspheres, and flow direction of fluid in microchannel, are key parameters affecting the flow and aggregation behaviors of the microspheres in microchannel during the phase transition. If a proper combination of these parameters is designed, the microspheres can aggregate together during the phase transition and stop automatically at a desired position in the microchannel by local heating, which is what the targeting drug delivery system expected. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Preparation, characterization, and binding profile of molecularly imprinted hydrogels for the peptide hepcidinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2010Vincenzo Abbate Abstract Molecularly imprinted hydrogels for the capture of the peptide hormone hepcidin were prepared by water-in-oil (w/o) suspension polymerization under mild conditions. Spherical and relatively uniformly sized gel beads were routinely obtained after optimization of the synthetic methodology. The polymers were analyzed by Fourier transform infrared spectroscopy, optical microscopy, and scanning electron microscopy. Although the imprinted materials exhibited higher affinity towards the epitope template (hepcidin N -terminus) than their corresponding blank polymers, the full-length target peptide was found strongly bound to all the hydrogels tested. However, by using whole fluorescent hepcidin as the print species, the imprinting effect was more pronounced. Moreover, bovine serum albumin did not bind to the poly N -isopropylacrylamide (PNIPAm)-based polymers. Thus, polymeric "sponges" for biomacromolecules with size-exclusion effect were developed, useful for peptide concentration, immobilization and/or purification from serum samples. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1721,1731, 2010 [source] Synthesis of magnetic, reactive, and thermoresponsive Fe3O4 nanoparticles via surface-initiated RAFT copolymerization of N -isopropylacrylamide and acroleinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2010Zhong-Peng Xiao Abstract A reversible addition-fragmentation chain transfer (RAFT) agent was directly anchored onto Fe3O4 nanoparticles in a simple procedure using a ligand exchange reaction of S -1-dodecyl- S,-(,,,,-dimethyl-,,-acetic acid)trithiocarbonate with oleic acid initially present on the surface of pristine Fe3O4 nanoparticles. The RAFT agent-functionalized Fe3O4 nanoparticles were then used for the surface-initiated RAFT copolymerization of N -isopropylacrylamide and acrolein to fabricate structurally well-defined hybrid nanoparticles with reactive and thermoresponsive poly(N -isopropylacrylamide- co -acrolein) shell and magnetic Fe3O4 core. Evidence of a well-controlled surface-initiated RAFT copolymerization was gained from a linear increase of number-average molecular weight with overall monomer conversions and relatively narrow molecular weight distributions of the copolymers grown from the nanoparticles. The resulting novel magnetic, reactive, and thermoresponsive core-shell nanoparticles exhibited temperature-trigged magnetic separation behavior and high ability to immobilize model protein BSA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 542,550, 2010 [source]
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