沉淀聚合法制备VCL／NVP温敏型微凝胶及其性能研究

用沉淀聚合法,以N-乙烯基己内酰胺（VCL）和N-乙烯基吡咯烷酮（NVP）为共聚单体、N,N-亚甲基双丙烯酰胺（MBA）为交联剂,通过改变交联剂的量制备了-系列不同粒径的温敏型微凝胶。用纳米颗粒力度分析仪（DLS）和原子粒显微镜（AFM）对凝胶进行了表征。结果表明：粒子为球型单分散;在15—55℃范围内凝胶粒径随温度升高而减小,具有温度敏感性,最低临界转变温度（LCST）为35℃;交联剂的量不改变最低临界转变温度,只改变粒子大小。     

Fast, multi-responsive microgels based on photo-crosslinkable poly(2-(dimethylamino)ethyl methacrylate)

Multi-responsive microgels based on poly(2-(N,N-dimethylamino)ethyl methacrylate) were developed and their properties were investigated. The primary goal of this research was to speed up the stimulus-response time of the hydrogels to a level usable for actuator applications, by reducing the diffusion distance of water. The gels were prepared by a UV induced photodimerization of a copolymer of 2-(dimethylamino)ethyl methacrylate and 4-cinnamoyl-phenyl methacrylate. Patterning studies showed that these materials can be used as photo-resist materials with high resolution at short exposure times. They showed lower critical solution temperature behavior in water, as well as pH dependent solubility and swelling ratios. While 1 mm thick gels showed response times to temperature and pH-changes of several hours, Si-supported microgels of 300 nm thickness had response times in the range of only a few seconds. The copolymer was prepared by free radical copolymerization, and the reactivity ratios were determined with the extended Kelen Tudos method. Spin-coating of this copolymer on Si supports and subsequent UV-irradiation yielded microgels of variable thickness (200 nm-15 μm), which was determined by confocal scanning laser microscopy. Surface plasmon resonance spectroscopy measurements demonstrated the fast, stimuli-responsive swelling behavior, while differential scanning calorimetry gave insight into the morphology of the networks.     

Microgel/clay nanohybrids as responsive scavenger systems

Microgel-clay composite particles were prepared by one-step surfactant-free precipitation polymerization. Laponite nanoparticles present in the reaction mixture become encapsulated during the microgel formation process. Microgel-clay composites based on poly(N-vinylcaprolactam-co-acetoacetoxyethyl methacrylate) containing different amount of incorporated clay nanoparticles were synthesized. The clay content was varied from 2 wt% to 18 wt%. The extremely high incorporation efficiency of the clay nanoparticles into microgels was detected. The size of the hybrid microgels was decreased from 700 nm to 100 nm by increase of the clay concentration in the reaction mixture. Obtained hybrid microgels exhibit negative surface charge and excellent colloidal stability. Microgel-clay composite particles display temperature-sensitive behaviour in water. The swelling degree of the hybrid microgels decreases with increase of the clay loading. Microgel-clay composite particles exhibit temperature-controlled uptake of the cationic dye, Methylene blue, and can be used as scavenger systems in aqueous media.     

On the structure of biocompatible,thermoresponsive poly(ethylene glycol) microgels

The aim of the present study is the preparation and characterization of microgel particles which are, contrary to other microgels, thermoresponsive as well as biocompatible. Hence, monodisperse p-MeO₂MA-co-OEGMA microgel particles were synthesized by precipitation polymerization. Swelling/deswelling behavior and the structure of poly(ethylene glycol) (PEG) based microgel particles were investigated. A combination of dynamic light scattering (DLS) and small angle neutron scattering (SANS) was used. Particle size and the volume phase transition temperature (VPTT) are adjustable by changing the amount of comonomer. SANS measurements indicate an inhomogeneous structure of the PEG microgels in the swollen state. At temperatures above the VPTT a compact structure was observed. An increase of the comonomer content leads to a densely packed core and a fuzzy shell in the swollen state. Additionally, nanodomains inside the polymer network were observed in the temperature range around the volume phase transition (VPT). Due to this heterogeneous structure in the swollen state two correlation lengths of the network fluctuations were observed.     

Garnet particles effect on the cross-linking of PDMS and the network structures formed

Poly(dimethylsiloxane) (PDMS) cross-linked films with different concentrations of micrometer-sized garnet particles were prepared through hydrosilylation reaction between a di-vinyl-terminated PDMS and a four-functional silane cross-linker in the presence of a Platinum catalyst. The garnet particles, consisting of micrometer-sized Ce doped Y₃Al₅O₁₂ particles commonly used on light converters (for solid state light devices, e.g. Light emitting diodes LEDs), were homogeneously and individually dispersed through the bulk of the cross-linked films for a concentration up to 20% in volume.The effect of the garnet on the cross-linking of the composite films was investigated by in-situ ATR-FTIR Spectroscopy. When formulations with an excess of cross-linker were used the overall consumption of Si-H groups of the cross-linker is slowdown in the presence of the garnet. The same effect was observed for an increasing concentration of the garnet. This effect is attributed to a strong interaction of the catalyst with the garnet during the cross-linking process. The possible origins of this interaction are discussed.NMR Imaging was used to investigate the cross-linked networks formed in the composite films. All the networks are homogeneous through the depth of the cross-linked composite films (approx. 5 μm resolution). The films prepared in the presence of the garnet particles showed similar relaxation behavior, regardless of the cross-linker concentration used in the initial formulation, contrary to previous results with PDMS cross-linked films. This behaviour is explained based on the presence of different type of chemical cross-links, resulting from the occurrence of hydrosilylation and secondary reactions, which are influenced by the interaction between the garnet particles and the catalyst.     

Morphology and drug release behavior of <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide/acrylic acid copolymer as stimuli-responsive nanogels

Thermo- and pH-responsive N-isopropylacrylamide (NIPAM) nanogels can be obtained by copolymerization of acrylic acid (AA) comonomer through differential microemulsion polymerization. The effects of comonomer, cross-linker, surfactant contents, and water/oil ratio were preliminarily investigated by a 2⁴ full factorial design in order to eliminate the insignificant parameters from the polymerization analysis. The smallest poly(NIPAM-co-AA) nanogel particles were 40 ± 1 nm in diameter with 6 wt% of solid content and 98% conversion without coagulation. The comonomer amounts controlled the morphologies and LCST of the poly(NIPAM-co-AA) nanogels. The hairy microgels of poly(NIPAM-co-AA) with a 10:90 mol ratio of AA/ NIPAM had a lower critical solution temperature (LCST) of 6 °C. With an increase in the AA amount to a 17 mol ratio, the LCST increased to 27 °C, resulting in core-shell morphology. The morphology of resultant nanogels was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and differential scanning calorimetry. Nuclear magnetic resonance spectroscopy was used to calculate the mole ratio of NIPAM and AA in resultant nanogels after dialysis. Both nanogel mole ratio and morphology effectively retained the cationic anti-cancer drug of methylene blue for several hours, an important basic requirement for a drug delivery system. Compared to core-shell microgels, a higher methylene blue release was obtained from the hairy microgels in simulated intestinal fluid.     

Thermo‐ and pH‐responsive microgels for controlled release of insulin

Microgel particles were prepared, made of hydroxypropylcellulose‐graft‐(acrylic acid) (HPC‐g‐AA) and acrylic acid(AA). The particles undergo reversible volume phase transitions in response to both pH and temperature changes while keeping the inherent properties of PAA and HPC‐g‐AA. Dynamic light scattering measurements reveal that the average hydrodynamic radius and hydrodynamic radius distributions of the microgel particles depend on temperature and pH. The microgels exhibit excellent pH sensitivity and a higher swelling ratio at higher pH in aqueous solution. In vitro release study shows that the amount of insulin released from the microgels is less at pH = 1.2 than at pH = 6.8. The results indicate that the resultant microgels seem to be of great potential for intelligent oral drug delivery. Copyright © 2012 Society of Chemical Industry     

Nanostructured CuO thin film electrodes prepared by spray pyrolysis: a simple method for enhancing the electrochemical performance of CuO in lithium cells

Nanostructured CuO thin films were prepared by using a spray pyrolysis method, copper acetate as precursor and stainless steel as substrate. The textural and structural properties of the films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The SEM images revealed thorough coating of the substrate and thickness of 450-1250 nm; the average particle size as determined from the AFM images ranged from 30 to 160 nm. The XRD patterns revealed the formation of CuO alone and the XPS spectra confirmed the presence of Cu²⁺ as the main oxidation state on the surface. The films were tested as electrodes in lithium cells and their electrochemical properties evaluated from galvanostatic and step potential electrochemical spectroscopy (SPES) measurements. The discharge STEP curves exhibited various peaks consistent with the processes CuO ⇔ Cu₂O ⇔ Cu and with decomposition of the electrolyte, a reversible process in the light of the AFM images. The best electrode exhibited capacity values of 625 Ah kg⁻¹ over more than 100 cycles. This value, which involves a CuO ⇔ Cu reversible global reaction, is ca. 50% higher than that reported for bulk CuO. The nanosize of the particles and the good adherence of the active material to the substrate are thought to be the key factors accounting for the enhanced electrochemical activity found.     

Monitoring of swelling of interpenetrating polymer network of polyethylene/poly(styrene-co-butylmethacrylate) (PE/P(S-co-BMA)) in toluene and cyclohexane using fluorescence spectroscopy

A real-time monitoring of excimer emission fluorescence probe di(1-pyrenemethyl)ether (DiPyM) was used for study swelling interpenetrating polymer network (IPN) consisting of polyethylene/poly(styrene-co-butylmethacrylate) (PE/P(S-co-BMA)) and containing different network density. DiPyM was introduced into IPN during polymerisation or was penetrated into blocks from toluene solution. The effect of solvent quality for swelling of IPN and density of IPN network was also studied. From steady-state measurements of monomer and excimer emission ratio (I_e/I_m), no difference was found between rate of swelling IPN with 0.5, 1 and 3 mol% of cross-linker. The rate of IPN swelling seems to be rather high. Some differences was found at real-time monitoring of excimer emission (λ_em=495 nm) of DiPyM measured during desorption of DiPyM from swelled IPN blocks. At higher content of cross-linker, a slower rate of DiPyM desorption from IPN matrix was observed.     

Synthesis of cross-linked poly(4-vinylpyridine) and its copolymer microgels using supercritical carbon dioxide: Application in the adsorption of copper(II)

Compared with conventional precipitation polymerization method, cross-linked poly(4-vinylpyridine) (P4VP) and its microgels copolymerized with α-methacrylic acid (MAA) were synthesized through a new route of stabilizer-free polymerization in supercritical fluids. The yellow, dry, fine powders were directly obtained from precipitation polymerization of 4-vinylpyridine in supercritical carbon dioxide (scCO₂) at pressures ranging from 70.0 to 230 bar, using N,N′-methylenebisacrylamide as cross-linker. The effects of the reaction pressure, cross-linker ratio, initiator concentration, and reaction time were investigated. The capacity of this microgel for adsorption of copper(II) was also studied. At higher cross-linker concentrations, a high yield of the cross-linked P4VP microgel was generated in scCO₂, and its particle size was less than 300 nm. Polymerization of cross-linked P4VP in scCO₂ was extremely sensitive to the density of the continuous phase. The adsorption followed the Langmuir isotherm. The adsorption capacities of cross-linked P(4VP-co-MAA) and cross-linked P4VP were 47.2 and 26.9 mg g⁻¹, respectively.     

Electrochemical and thermal properties of polymer electrolytes based on poly(epichlorohydrin-co-ethylene oxide-co-ally glycidyl ether)

A series of novel electrolytes based on the terpolymer host, poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) with lithium perchlorate and lithium bis(trifluoromethanesulfonyl)imide have been prepared and characterized by conductivity measurements, cyclic voltammetry at a gold microelectrode and thermal analysis.Electrolyte compositions, represented as p(EEO-AGE)LiX(wt%), were produced with lithium salt compositions between 0.5 and 53 wt% (where wt% indicates amount of lithium salt present in the epichlorohydrin-co-ethylene oxide-co-allyl glycidyl host matrix). The guest salt and host polymer were dissolved in tetrahydrofuran and cast to produce thin, free-standing electrolyte films.The p(EEO-AGE)LiX(wt%) (X = ClO₄ and TFSI) electrolytes showed encouraging levels of ionic conductivity and acceptable thermal stability. Electrolytes based on this host polymer were obtained as completely amorphous films with good mechanical properties.     

An antibacterial composite system based on multi-responsive microgels hosting monodisperse gold nanoparticles

A multi-responsive microgel having response to pH, temperature, and salt concentration was successfully prepared using a water-soluble monomer. Microgels were readily prepared from 2-(N-morpholino)ethyl methacrylate (MEMA) via emulsion polymerization using glycidyl methacrylate as a comonomer cross-linker. The morpholino groups of MEMA residues of microgels were able to give complexation with metal containing anions such as AuCl₄ ^? in acidic conditions. The reduction of aurate ions with sodium borohydride led to immobilized-gold nanoparticles (AuNP) in the microgel system. Average particle diameters of AuNPs were determined to be 10 ± 2 nm. The resulting AuNP-microgel system was examined as a nanoreactor for catalyst system and determined to be very effective in the reduction of 4-nitrophenol model reaction in aqueous media. AuNPs-microgel composite system had antibacterial properties against several Gram-positive and Gram-negative bacteria similar to amoxicillin. This P(MEMA-co-GMA) microgel is also very useful for different applications such as a host for metal nanoparticle production, a drug carrier or drug delivery system.     

Synthesis and characterization of thermosensitive poly(N-isopropylacrylamide-co-hydroxyethylacrylamide) microgels as potential carriers for drug delivery

Thermoresponsive colloidal microgels were prepared by precipitation copolymerization of N-isopropylacrylamide (NIPAM) and N-hydroxyethylacrylamide (HEAM) with various concentrations of a cross-linker in the presence of an anionic surfactant, sodium dodecylsulphate (SDS). The volume phase transition temperature (VPTT) of the prepared microgels was studied by dynamic light scattering (DLS), ultraviolet–visible spectroscopy (UV–vis) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. In addition, atomic force microscopy (AFM) was used to characterize the polydispersity and morphology of the microgels. Results indicated that poly(NIPAM-co-HEAM) microgels are spherical and monodisperse. VPTTs of microgels determined by DLS and UV–vis methods are almost the same and very close to the human body temperature, presenting the microgels as candidates for biomedical application. The temperature at which the phase transition occurred is nearly independent of the cross-linking density, whereas the transition range is deeply influenced by temperature. Also, the SDS concentration was increased to decrease the average hydrodynamic size of the microgels, due to the electrostatic repulsion between the charged particles during the polymerization process. ¹H-NMR spectra of the microgels show a decrease in peak intensity with an increased temperature due to a reduction in molecular mobility of the polymer segments. Release rates of propranolol from microgels are deeply influenced by temperature; below the VPTT at 25 °C, the drug is rapidly released at a rate comparable to that of a free drug, whereas above the VPTT (37 and 42 °C), a fraction of the drug is mechanically expulsed in the first five min, followed by a prolonged release.     

Fabrication of core or shell reversibly photo cross-linked micelles and nanogels from double responsive water-soluble block copolymers

Poly(butanedioic acid, 1-[3-[(2-methyl-1-oxo-2-propen-1-yl)oxy]propyl] ester)-b-poly(methoxydi(ethylene glycol) methacrylate-co-4-methyl-[7-(methacryloyl)oxyethyloxy] coumarin) (PSPMA-b-P(DEGMMA-co-CMA)) block copolymer was synthesized via atom transfer radical polymerization (ATRP). The temperature and pH responsive micellization behaviors of PSPMA-b-P(DEGMMA-co-CMA) were investigated to obtain P(DEGMMA-co-CMA)-core and PSPMA-core micelles. After the two types of micelles were exposed to 365 nm UV light, core cross-linked (CCL) micelles and shell cross-linked (SCL) micelles were facilely prepared. The photo cross-linking was proved to be reversibly controlled under alternative irradiation of 365 nm and 254 nm UV light. More interestingly, block copolymer nanogels were fabricated by translating the hydrophobic core of the CCL and SCL micelles into hydrophilic via adjusting the temperature and pH. The sizes of the block copolymer nanogels can be facilely controlled by UV light irradiation. The introduction of reversibly photo cross-linkable groups into the double responsive block copolymers provides a novel approach to develop more sophisticated, controllable, and smarter nanocarriers that might have great potentials in biomedical applications.     

Preparation and thermal response behavior of poly(N‐isopropylacrylamide‐co‐a crylic acid) microgels via soap‐free emulsion polymerization based on AIBN initiator

Poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAM‐co‐AA)) microgels with different copolymer compositions were prepared through soap‐free emulsion polymerization at 80°C, and 2, 2′‐azobisisobutyronitrile (AIBN) was used as initiator. Scanning electron microscope (SEM) characterization shows that the prepared microgels are regular and smooth and not easy to distort. Result of ¹H‐NMR characterization shows that with increasing of the initial concentration of AA (AA in feed), the AA content in polymer chains increases. The thermal response of microgels latex was investigated by UV‐3010 spectrophometer through detecting the transmittance of the latex at different temperature in the range of 190–900 nm. The thermal response of the poly(NIPAM‐co‐AA) microgels was tested by dynamic light scattering (DLS). The results show that with the increase of AA content in polymer chains, the low critical solution temperature (LCST) of microgels latex first decreases and then increases. Still, with increasing of AA in poly(NIPAM‐co‐AA) microgels, the LCST of microgels first increases and then decreases. The basic reasons causing the changes of LCST of microgels latex and microgels are interpreted clearly in this article from the perspective of hydrogen bonding interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Temperature‐induced volume change and glucose sensitivity of poly[(N‐isopropylacry‐ lamide)‐co‐acrylamide‐co‐(phenylboronic acid)] microgels

Nearly monodisperse glucose‐sensitive poly[(N‐isopropylacrylamide)‐co‐acrylamide‐co‐(phenylboronic acid)] microgels were synthesized in aqueous media by the functionalization of poly[(N‐isopropylacrylamide)‐co‐acrylamide‐co‐(acrylic acid)] microgels with 3‐aminophenylboronic acid via carbodiimide coupling. The glucose‐sensitive and thermosensitive behaviour of the microgels was investigated using a dynamic light scattering technique. The introduction of the hydrophobic phenylboronic acid (PBA) group significantly decreases the temperature at which maximum volume change of the resultant microgel particles is observed. The glucose sensitivity of the PBA‐containing microgels relies on the stabilization of the charged phenylborate ions by binding with glucose, which can convert more hydrophobic PBA groups to the hydrophilic phenylborate ions. The effect of pH, ionic strength and PBA content on temperature‐induced volume change and glucose sensitivity was systemically studied. The effect of NaCl on the glucose sensitivity was also investigated at physiological pH and ionic strength. Copyright © 2011 Society of Chemical Industry     

Interfacial Chemistry of Langmuir-Blodgett Deposited Polyimide Films on Si (100)

Using the Langmuir-Blodgett (LB) technique, ultrathin films of the octadecylammonium salt of polyamic acid (PACS) on (100) oriented silicon wafers with one, three and five monolayers were prepared. The imidization of the films was investigated with x-ray photoelectron spectroscopy (XPS) during a stepwise heating procedure in vacuum. Significant differences in the XPS spectra indicate an incomplete polymerization of the films as a function of film thickness. It is believed that the chemical interaction at the interface between Si substrate and PACS is responsible for the incomplete polymerization of the LB film in direct contact with the substrate. From ellipsometric measurements the absolute thickness of a PACS and a polyimide layer has been determined to be 1.7 nm and 0.6nm, respectively. These measurements allow us to determine the electron mean free path for the Si2p electrons (E_k=1153 eV) of λ = 4.2±0.1 nm through these films.     

Influence of ethyl methacrylate content on the volume‐phase transition of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] microgels

A novel series of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] (p(NIPAM‐co‐EMA)) microgels was prepared by the surfactant‐free radical polymerization of N‐isopropylacrylamide (NIPAM) with ethyl methacrylate (EMA). The shape, size dispersity and volume‐phase transition behavior of the microgels were investigated by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The transmission electron micrographs and DLS results showed that microgels with narrow distributions were prepared. It was shown from UV–Vis, DLS and DSC measurements that the volume‐phase transition temperature (VPTT) of the p(NIPAM‐co‐EMA) microgels decreased with increasing incorporation of EMA, but the temperature‐sensitivity was impaired when more EMA was incorporated, causing the volume‐phase transition of the microgels to become more continuous. It is noteworthy that incorporation of moderate amounts of EMA could not only lower the VPTT but also enhance the temperature‐sensitivity of the microgels. The reason for this phenomenon could be attributed to changes in the complicated interactions between the various molecules. Copyright © 2004 Society of Chemical Industry     

Interfacial Chemistry of Langmuir-Blodgett Deposited Polyimide Films on Si (100)

Using the Langmuir-Blodgett (LB) technique, ultrathin films of the octadecylammonium salt of polyamic acid (PACS) on (100) oriented silicon wafers with one, three and five monolayers were prepared. The imidization of the films was investigated with x-ray photoelectron spectroscopy (XPS) during a stepwise heating procedure in vacuum. Significant differences in the XPS spectra indicate an incomplete polymerization of the films as a function of film thickness. It is believed that the chemical interaction at the interface between Si substrate and PACS is responsible for the incomplete polymerization of the LB film in direct contact with the substrate. From ellipsometric measurements the absolute thickness of a PACS and a polyimide layer has been determined to be 1.7 nm and 0.6nm, respectively. These measurements allow us to determine the electron mean free path for the Si2p electrons (E_k=1153 eV) of λ = 4.2±0.1 nm through these films.     

Emulsifier‐free poly[2‐(diethylamino)ethyl methacrylate] microgels with cationic quaternary ammonium monomers

Although poly[2‐(diethylamino)ethyl methacrylate] (PDEA) microgels are biocompatible and show potential in drug delivery, little research exists with respect to their preparation. Therefore, emulsifier‐free PDEA microgels were synthesized in the presence of cationic ammonium salts of 2‐(dimethylamino)ethyl methacrylate (DMA) that were quaternized with 1‐bromohexadecane, 1‐bromooctadecane, 1‐bromopentane, or benzyl chloride. These served as both comonomers and polymerizable surfactants, providing colloidal stability to the DEA droplets during polymerization. The stability of the microgel particles in different pH values between 4 and 11 was investigated by turbidity–wavelength measurements. The benzyl group containing monomer was the most stabilizing. The pH‐responsive behavior of the microgels in dilute aqueous solution was examined with respect to the amount of DEA, amount of copolymer, type of copolymer, and water content. Most of the microgels remain colloidally stable up to a pH of 9.0, while particles are less than 300 nm in size at pH 8.0. The isoelectric points of the microgels are higher than 8.5 in most cases. In fact, this value exceeds 12.0 by modifying the amount of copolymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43196.