一步法制备PNIPAAm-g-PAN/PSt载银复合微球及其抗菌性能研究

以AgNO3为金属源,通过乙醇将与聚N-异丙基丙烯酰胺接枝聚丙烯腈/聚苯乙烯（PNIPAAm-g-PAN/PSt）聚合物微球表面酰胺基团配位的银离子（Ag+）还原,一步法制备了PNIPAAm-g-PAN/PSt载银复合微球。通过傅立叶变换红外（FTIR）和紫外-可见光光谱表征发现,由Ag+还原所得的Ag纳米颗粒被成功地固载在PNIPAAm-g-PAN/PSt 微球上;用透射电子显微镜（TEM）对载银微球的大小和形态进行了表征;热重分析（TGA）结果表明,固载在微球表面的银纳米颗粒的含量（质量分数）为12%;抗菌实验结果表明,所制备的载银微球具有抗革兰氏阴性菌的活性。     

A novel sodium carboxymethylcellulose/poly(N‐isopropylacrylamide)/Clay semi‐IPN nanocomposite hydrogel with improved response rate and mechanical properties

A novel semi‐IPN nanocomposite hydrogel (CMC/PNIPA/Clay hydrogel) based on linear sodium carboxymethylcellulose (CMC) and poly(N‐isopropylacrylamide) (PNIPA) crosslinked by inorganic clay was prepared. The structure and morphology of these hydrogels were investigated and their swelling and deswelling kinetics were studied in detail. TEM images showed that the clay was substantially exfoliated to form nano‐dimension platelets dispersed homogeneously in the hydrogels and acted as a multifunctional crosslinker. The CMC/PNIPA/Clay hydrogels swell faster than the corresponding PNIPA/Clay hydrogels at pH 7.4, whereas they swell slower than the PNIPA/Clay hydrogels at pH 1.2. The CMC/PNIPA/Clay nanocomposite hydrogels showed much higher deswelling rates, which was ascribed to more passway formed in these hydrogels for water to diffuse in and out. The deswelling process of the hydrogels could be approximately described by the first‐order kinetic equation and the deswelling rate decreased with increasing clay content. The mechanical properties of the CMC/PNIPA/Clay nanocomposite hydrogels were analyzed based on the theory of rubber elasticity. It was found that with increasing clay content, the effective crosslink chain density, v_e, increased whereas the molecular weight of the chains between crosslinks M_c decreased. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1546–1555, 2008     

Preparation of Polymer Nanofibers Containing Silver Nanoparticles by Using Poly(N‐vinylpyrrolidone)

Summary: Poly(N‐vinylpyrrolidone) (PVP) was used in two methods to prepare polymer nanofibers containing Ag nanoparticles. The first method involved electrospinning the PVP nanofibers containing Ag nanoparticles directly from the PVP solutions containing the Ag nanoparticles. N,N‐Dimethylformamide was used as a solvent for the PVP as well as a reducing agent for the Ag⁺ ions in the PVP solutions. In the second method, poly(vinyl alcohol) (PVA) aqueous solutions were electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles. The Ag nanoparticles were evenly distributed in the PVA nanofibers. PVP containing Ag nanoparticles could be used to introduce Ag nanoparticles to other polymer nanofibers that are miscible with PVP.

TEM image of a PVA nanofiber electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles.     

Fabrication of Micropatterned Gold Nanoparticle Arrays as a Template for Surface‐Initiated Polymerization of Stimuli‐Responsive Polymers

Summary: This paper demonstrates a new, reliable, and simple method for fabricating micropatterned nanoparticle arrays that can serve as templates for the surface‐initiated polymerization of polymer brushes. As a proof of concept, we micropatterned gold nanoparticles (Au‐NPs, ≈10 nm) onto glass, silicon, polystyrene, and gold surfaces by a simple three‐step process: (1) microcontact printing of soluble polymer, (2) incubation with a solution of Au‐NPs, and (3) lift‐off of the template in a mixture of ethanol and deionized water. 40 µm wide features were successfully fabricated without any significant defects or nonspecific adsorption on the background. To demonstrate the utility of these Au‐NP templates, we subsequently polymerized N‐isopropylacrylamide by surface‐initiated polymerization, using a surface‐bound initiator.

Synthesis of PNIPAAm brushes from micropatterned Au‐NP.     

Dual temperature‐ and pH‐sensitive hydrogels from interpenetrating networks and copolymerization of N‐isopropylacrylamide and sodium acrylate

Hydrogels responsive to both temperature and pH have been synthesized in the forms of sequential interpenetrating networks (IPNs) of N‐isopropylacrylamide (NIPAAm) and sodium acrylate (SA) and compared with the crosslinked random copolymers of N‐isopropylacrylamide and SA. Whereas the stimuli‐sensitive behaviors of copolymer hydrogels were strongly dependent on the ionic SA contents, the IPN hydrogels exhibited independent swelling and thermal behaviors of each network component. The sequences and media in the synthesis of IPNs influenced the swelling capacities of the IPNs, but not the temperature or pH ranges at which the swelling changes occurred. In IPNs, a more expanded primary gel network during the synthesis of the secondary network contributed to the better swelling of the final IPNs. Both the swelling and thermal behaviors of the IPNs suggest that poly(N‐isopropylacrylamide) and poly(sodium acrylate) are phase separated regardless of their synthesis conditions. The presence of the poly(sodium acrylate) network did not influence the temperature or the extent of phase transition of the poly(N‐isopropylacrylamide) network in the IPNs, but did improve the thermal stability of the IPNs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3293–3301, 2004     

Robust Poly(allylamine)‐graft‐poly(N‐isopropylacrylamide) Particles Prepared by Physical Crosslinking with Poly(styrene sulfonate)

Summary: Robust thermosensitive PAH‐g‐PNIPAAm/PSS particles were prepared by addition of a poly(allylamine)‐graft‐poly(N‐isopropylacrylamide) particle suspension into poly(styrene sulfonate) solution above the LCST of PAH‐g‐PNIPAAm. Scanning force microscopy revealed stable and well‐separated particles in water at room temperature. The zeta‐potential showed a negative surface charge of the particles. Their thermosensitive behavior was demonstrated by dynamic light scattering. The release of rhodamine 6G loaded particles could respond to the incubation temperature.

Fabrication of thermosensitive and robust particle by suspension of in situ formed PAH‐g‐PNIPAAm particle above the LCST in PSS solution.     

Preparation and properties of poly(N‐isopropylacrylamide)/poly(N‐isopropylacrylamide) interpenetrating polymer networks for drug delivery

A novel poly(N‐isopropylacrylamide) (PNIPA)/PNIPA interpenetrating polymer network (IPN) was synthesized and characterized. In comparison with conventional PNIPA hydrogels, the shrinking rate of the IPN hydrogel increased when gels, swollen at 20 °C, were immersed in 50 °C water. The phase‐transition temperature of the IPN gel remained unchangeable because of the same chemical constituent in the PNIPA gel. The reswelling kinetics were slower than those of the PNIPA hydrogel because of the higher crosslinking density of the IPN hydrogel. The IPN hydrogel had better mechanical strength because of its higher crosslinking density and polymer volume fraction. The release behavior of 5‐fluorouracil (5‐Fu) from the IPN hydrogel showed that, at a lower temperature, the release of 5‐Fu was controlled by the diffusion of water molecules in the gel network. At a higher temperature, 5‐Fu inside the gel could not diffuse into the medium after a burst release caused by the release of the drug on the surface of the gel. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1249–1254, 2004     

Rapid and controlled deswelling of porous poly(N‐isopropylacrylamide) hydrogels prepared by the templating of interpenetrated nanoporous silica particles

Free radical polymerization of N‐isopropylacrylamide (NIPAAm) and crosslinker solutions, which were fulfilled in silica particles with an interpenetrated and nanometer‐sized porous structure (a diameter of 3 mm and mean pore sizes of 15, 30, and 50 nm), fabricated hybrids of organic hydrogels and inorganic silica. Differential scanning calorimetric analyses of the hybrids revealed that silica components affected the thermoresponsive properties of polyNIPAAm hydrogels. Porous polyNIPAAm hydrogels were prepared by the subsequent acid treatment of the hybrids to remove silica. Transmission Fourier transformed infrared spectra indicated the selective extraction of silica. Scanning electron microscopic observation of the hydrogels confirmed the porous structure. The deswelling rate of porous hydrogels was 7 times larger than that of conventional hydrogels and increased with increasing the pore size of silica used. However, the swelling was not affected by the pore formation. The thermoresponsiveness of porous polyNIPAAm hydrogels could be regulated by the pore size. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3542–3547, 2002     

The effect of water content on the ultimate properties of rubbery nanocomposite gels

An investigation was conducted into the effects of water content (R) on the ultimate tensile properties of nanocomposite hydrogels (NC gels) based on poly(N‐isopropylacrylamide)/clay networks. Rubbery NC gels with low clay contents (<NC10) exhibited unique changes in their stress–strain curves, depending on the R. At high R, where PNIPA chains are fully hydrated, NC gels retained their rubbery tensile properties, whereas they changed to exhibit plastic‐like deformations with decreasing R. Consequently, for a series of NC gels with different R, a failure envelope was obtained by connecting the rupture points in the stress–strain curves. Here, the counterclockwise movement was observed as either the R decreased or the strain rate increased. This seemed to be analogous to that of a conventional elastomer (e.g., SBR), although the mechanisms are different in the two cases. From the R and C_clay dependences of the ultimate properties, three critical values of R were defined, where R showed a maximum strain at break, a steep increase in initial modulus, and onset of brittle fracture. Compared with NC gels, OR gels (chemically crosslinked hydrogels) showed similar but very small changes in their stress–strain curves on altering R, whereas LR (viscous PNIPA solution) showed a monotonic decrease (increase) in ε_b (E_i) with decreasing R. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2328–2340, 2009     

Effect of the crosslinking level on the properties of temperature‐sensitive poly(N‐isopropylacrylamide) hydrogels

In this study, the effect of the level of crosslinking on the properties of poly(N‐isopropylacrylamide) (PNIPAAm) hydrogels was investigated in terms of their lower critical solution temperature (LCST), interior morphology, equilibrium swelling, and deswelling and swelling kinetics. The thermal analysis showed that PNIPAAm hydrogels, having a wide range of crosslinking levels, exhibited almost the same LCSTs, and this was different from what the conventional theory would have predicted. Scanning electron micrographs revealed that the interior network structure of the PNIPAAm matrix became more porous with an increase in the level of crosslinking. This more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external temperature changes during the deswelling process and the swelling process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 582–593, 2003     

超声辐射法制备银纳米微粒

在有机介质十氢化萘中,以金属钠、硝酸银和油酸钠为起始原料,通过超声辐射使金属钠和硝酸银发生置换反应,成功制备了油酸表面修饰的Ag纳米微粒.采用透射电子显微镜、X射线粉末衍射仪和热分析仪对其形貌、结构和性能进行了表征.透射电镜和X射线粉末衍射研究表明:所制备的油酸表面修饰Ag纳米微粒粒径较小,平均尺寸为10 nm,分布均匀,无团聚现象,且具有面心立方晶型结构.热分析结果表明:所制备的样品含有约9.7%的有机物,并具有良好的热稳定性能.     

Newly designed hydrogel with both sensitive thermoresponse and biodegradability

The synthesis and characterization of thermoresponsive hydrogels on the basis of N‐isopropylacrylamide (IPAAm) copolymers crosslinked with biodegradable poly(amino acids) are described. This hydrogel was prepared with two kinds of reactive IPAAm‐based copolymers containing poly(amino acids) as the side‐chain groups and activated ester groups. We introduced the graft chains by decarboxylation polymerization of amino acid N‐carboxyanhydrides initiated from lateral amino groups in the PIPAAm copolymer. The hydrogels easily crosslinked with degradable poly(amino acid) chains by only mixing the copolymer aqueous solutions. The gelling method in this study would provide some of the following innovative features: (1) no necessary removal of unreacted monomers and so forth, (2) simpler loading of drugs into the hydrogels (only mixing when gelling), and (3) easier insertion into the body. On the basis of the swelling ratio measurement of the hydrogel, large volume changes dependent on temperature changes were observed. Moreover, the enzymatic temperature‐dependent degradation was confirmed. The results suggested that these hydrogels could be used for an injectable or implantable matrix of temperature‐modulated drug release. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 779–787, 2003     

Crosslinked Poly(ionic liquid) Nanoparticles: Inner Structure,Size, and Morphology

In this contribution, we present the highly ordered inner structure of crosslinked poly(ionic liquid) nanoparticles. Cryogenic transmission electron microscopy revealed that they resembled centric multilamellar vesicles of different geometries, depending on the exact length of the quaternizing alkyl chains. The nanoparticle size was found to be sensitive to the polymerization conditions, such as the concentrations of monomers and crosslinking agents, the anion type and the externally added salt, but fairly inert to the polymerization temperature and the amount of initiator. The size expansion of the nanoparticles in different polymerization runs was found to be either isotropic or anisotropic via their linear attachment under certain polymerization conditions.     

High Density Polyethylene Containing Antibacterial Silver Nanoparticles for Medical Applications

High density polyethylene (HDPE) and composites with silver nanoparticles were processed via extrusion and injection moulding. The materials thus produced were tested against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. The release of silver ions Ag⁺ from composites was measured by means of ICP-MS method. Surface parameters such as wettability and roughness were determined because of their effect on the most important processes at biomaterial interface. Scanning electron microscopy was used to investigate the microstructure. Durability tests of polymer and composite materials were carried out in a simulated biological solution by monitoring the pH and electrical conductivity, mass changes as well as the longitudinal ultrasonic wave measurements. Antibacterial tests prove that nanosilver modified materials have bactericidal activity against tested bacteria. Biological durability studies reveal stable behavior of incubated materials. Spectrometric analysis shows that the amount of silver release depends on the immersion time and the amount of nanopowder introduced into the polymer matrix.     

Molecular Dynamics Investigation of the Thermo‐Responsive Polymer Poly(N‐isopropylacrylamide)

Using molecular dynamics simulations with an OPLS force field, the lower critical solution temperature (LCST) of single‐ and multiple‐chain PNIPAM solutions in water is investigated. The sample containing ten polymer chains shows a sudden drop in size and volume at 305 K. Such an effect is absent in the single‐chain system. Large fluctuations of the physical properties of a short single‐chain prevent any clear detection of the LCST for the chosen model system, at least on the time scale of 200 ns. The results provide evidence that a critical number of PNIPAM monomer units must be present in the simulated system before MD simulations are capable to detect conformational changes unambiguously.

     

Associative block copolymers comprising poly(N‐isopropylacrylamide) and poly(ethylene oxide) end‐functionalized with a fluorophilic or hydrophilic group. Synthesis and aqueous solution properties

A series of block copolymers comprising poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) end‐functionalized with a quaternary ammonium group (R_Q) was synthesized by free‐radical polymerization of N‐isopropylacrylamide with well‐defined R_QPEO macroazoinitiators. The radical termination occurred mainly by disproportionation, as confirmed by combining the data from size exclusion chromatography (SEC) and rheology measurements. The copolymers denoted R_QE_xN_y differ in type of the terminal group [F_Q = C₈F₁₇(CH₃)₂N⁺ or M_Q = (CH₃)₃N⁺] and in the length of the PEO (E_x; x = 4, 6, or 10 K) and PNIPAM (N_y; y = 7 or 17–19 K) blocks. The type of the terminal group determined the behavior of the block copolymers in the dilute and semidilute regime. Self‐assembled species formed by both F_Q and M_Q modified block copolymers were detected by static light scattering measurements at 25 °C and above the lower critical solution temperature (LCST). The LCST of the block copolymers depended on the type of the R_Q group and the length of the blocks. F_Q‐modified copolymers form elastic gels below and above the LCST. It was inferred that the F_Q groups and the PNIPAM blocks form segregated microdomains that serve as junctions to maintain a viscoelastic network. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5736–5744, 2004     

Phase Transition Behaviors of Self‐Oscillating Polymer and Nano‐Gel Particles

Summary: Self‐oscillating polymers and nano‐gel particles consisting of N‐isopropylacrylamide and the ruthenium catalyst of the Belousov‐Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self‐oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators.

Chemical structure of poly(NIPAAm‐co‐Ru(bpy)₃).     

Temperature-sensitive polyamidoamine dendrimer/poly(N-isopropylacrylamide) hydrogels with improved responsive properties

Novel temperature-sensitive poly(N-isopropylacrylamide)/amine-terminated polyamidoamine dendrimer G6-NH2 hydrogels with fast responsive properties were synthesized by forming semi-interpenetrating polymeric networks. In contrast to the conventional PNIPA hydrogel, these new gels showed rapid shrinking rate at the temperature above lower critical solution temperature (LCST), and exhibited higher equilibrium swelling ratio at room temperature. All these properties might be attributed to the incorporation of polyamidoamine dendrimer G6-NH2, which forms water-releasing channels and increases the hydrophilicity of PNIPA network. The novel hydrogels have potential applications in drug and gene delivery.     

Formation of a Polypseudorotaxane via Self‐Assembly of γ‐Cyclodextrin with Poly(N‐isopropylacrylamide)

A polypseudorotaxane (PPR) comprising γ‐cyclodextrin (γ‐CD) as host molecules and poly(N‐isopropylacrylamide) (PNIPAM) as a guest polymer is prepared via self‐assembly in aqueous solution. Due to the bulky pendant isopropylamide group, PNIPAM exhibits size‐selectivity toward self‐assembly with α‐, β‐, and γ‐CDs. It can fit into the cavity of γ‐CD to give rise to a PPR, but cannot pass through α‐CD and β‐CD under the same conditions. The ratio of the number of γ‐CD molecules to entrapped NIPAM repeat units is kept at 1:2.2 or 1:2.4, determined by ¹H NMR spectroscopy and TGA analysis, respectively, indicating that there are more than 2 but less than 3 NIPAM repeat units included by one γ‐CD molecule. This finding opens new avenues to PPR‐based supramolecular polymers to be used as solid, stimuli‐responsive materials.     

Synthesis of Silver and Gold Nanoparticles by a Novel Electrochemical Method

Spherical silver and gold nanoparticles with narrow size distributions were conveniently synthesized in aqueous solution by a novel electrochemical method. The technological keys to the electrochemical synthesis of monodispersed metallic nanoparticles lie in the choice of an ideal stabilizer for the metallic nanoclusters and the use of a rotating platinum cathode. Poly(N‐vinylpyrrolidone) (PVP) was chosen as the stabilizer for the silver and gold clusters. PVP not only protects metallic particles from agglomeration, but also promotes metal nucleation, which tends to produce small metal particles. Using a rotating platinum cathode effectively solves the technological difficulty of rapidly transferring the (electrochemically synthesized) metallic nanoparticles from the cathode vicinity to the bulk solution, avoiding the occurrence of flocculates in the vicinity of the cathode, and ensuring the monodispersity of the particles. The particle size and particle size distribution of the silver and gold nanoparticles were improved by adding sodium dodecyl benzene sulfonate (SDBS) to the electrolyte. The electrochemically synthesized nanoparticles were characterized by TEM and UV/Vis spectroscopy.