由铜-胺氧化还原引发反应一步法简便制备TiO_2表面接枝聚甲基丙烯酸甲酯纳米杂化粒子

提出并验证了一种通过普通自由基聚合在纳米TiO2表面接枝聚甲基丙烯酸甲酯的简单方法.通过在纳米TiO2粒子表面引入伯胺分子层(纳米TiO2-NH2粒子),利用Cu2+-胺氧化还原体系实现了CuSO4催化纳米TiO2-NH2粒子表面引发甲基丙烯酸甲酯(MMA)的自由基接枝聚合,从而一步得到表面固定有聚甲基丙烯酸甲酯链的纳米TiO2杂化粒子(纳米TiO2-PMMA杂化粒子).红外光谱、热失重分析与电镜的结果都表明PMMA已经被接枝到纳米TiO2粒子表面,且接枝率随着聚合时间的延长而逐渐增大,PMMA链的引入有助于降低纳米TiO2粒子微球的团聚程度、增强与有机溶剂分子的范德华力,从而提高分散稳定性.反应溶液中没有游离均聚物形成.     

Effect of the polymer matrix on the formation of silver nanoparticles in polymer–silver salt complex membranes

When polymer–silver salt complex membranes were exposed to UV irradiation, the separation performances of both the permeance and selectivity for propylene–propane decreased, which was primarily attributed to the reduction of the silver ions in the membranes to silver nanoparticles. Here, the effect of the polymer matrix on the formation of silver nanoparticles in the polymer–silver salt complex membranes was investigated. This effect was assessed for the complexes of two kinds of silver salts (AgBF₄ and AgCF₃SO₃) with several polymeric ligands containing three different carbonyl groups, including poly(vinyl pyrrolidone) (PVP) with an amide group, poly(vinyl methyl ketone) (PVMK) with a ketone group, and poly(methyl methacrylate) (PMMA) with an ester group. UV–vis spectra and transmission electron microscopy (TEM) images clearly indicated that the reduction rate of the silver ions has the following order in the various polymer matrices: PVP > PVMK > PMMA, whereas the size and the distribution of the nanoparticles exhibited the reverse order. The tendency to form silver nanoparticles was explained in terms of the differences between the comparative strengths of the interactions of the silver ions with the different carbonyl oxygens in the matrices, as well as that of the silver ions with counteranions, which was characterized by X‐ray photoelectron spectroscopy (XPS) and FT‐Raman spectroscopy. It was concluded that when the concentration of free silver ions was low due to weak polymer–silver ion and strong silver ion–anion interactions, as found with PMMA, the reduction rate of silver ions to silver nanoparticles was slow. Therefore, the PMMA–silver complex membranes were less sensitive to decreases in separation performance upon UV irradiation than compared to the PVP membranes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1168–1178, 2006     

Thermal and optical properties of silver-poly(methylmethacrylate) nanocomposites prepared by in-situ radical polymerization

Surface modified silver nanoparticles dispersed in chloroform were encapsulated in poly(methylmethacrylate) (PMMA) by in-situ radical polymerization of methyl methacrylate initiated by 2,2′-azobisisobutyronitrile. The particle size distribution of colloidal silver nanoparticles was determined using transmission electron microscopy. The obtained transparent nanocomposite films were characterized using UV-vis spectroscopy, ¹H NMR spectroscopy and gel permeation chromatography. Effective medium Maxwell-Garnett theory was used in order to explain optical properties of nanocomposite films taking into account inhomogeneous spatial distribution of silver nanoparticles in PMMA matrix. The influence of the silver nanoparticles on the thermal properties of the PMMA matrix was investigated using thermo-gravimetric analysis and differential scanning calorimetry. Thermo-oxidative stability of the PMMA in the presence of low content of inorganic phase is significantly improved. The glass transition temperatures of nanocomposites are slightly lower compared to the pure polymer.     

PREPARATION OF POLY（METHYL METHACRYLATE）/LAYERED DOUBLE HYDROXIDES NANOCOMPOSITES via in situ SOLUTION POLYMERIZATION

An exfoliated layered double hydroxides/poly(methyl methacrylate)(LDHs/PMMA)nanocomposite was prepared by in situ solution polymerization of methyl methacrylate(MMA)in the presence of 4-vinylbenzenesulfonate intercalated LDHs(MgAl-VBS LDHs).MgAl-VBS LDHs was prepared by the ion exchange method,and the structure and composition of the MgA1-VBS LDHs were determined by X-ray diffraction(XRD),infrared spectroscopy and elemental analysis.XRD and transmission electron microscopy(TEM)were employed to examine the structure of LDHs/PMMA nanocomposite.It was indicated that the LDHs layers were well exfoliated and dispersed in the PMMA matrix.The grafting of PMMA onto LDHs was confirmed by the extraction result and the weight fraction of grafted PMMA increased as the weight fraction of LDHs in the nanocomposites increased.     

Preparation of submicron polypyrrole/poly(methyl methacrylate) coaxial fibers and conversion to polypyrrole tubes and carbon tubes

In an effort to prepare electrically conductive nanofiber and nanotube materials, polypyrrole/poly(methyl methacrylate) coaxial fibers have been prepared using polymer fibers produced from an electrospinning process. Poly(methyl methacrylate) (PMMA) fibers with an average diameter of 230 nm were initially fabricated by electrospinning as core materials. The PMMA fibers were subsequently coated as templates with a thin layer of polypyrrole (PPy) by in-situ deposition of the conducting polymer from aqueous solution. Hollow PPy tubes were produced by dissolution of the PMMA core from PPy/PMMA coaxial fibers. High-temperature (1000 degrees C) treatment under inert atmosphere converted PPy/PMMA coaxial fibers into carbon tubes by complete decomposition of PMMA fiber core and carbonization of the PPy wall. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and FT-IR spectroscopy confirmed the formation of the PPy/PMMA coaxial fibers, PPy tubes, and carbon tubes.     

Tunable metallization by assembly of metal nanoparticles in polymer thin films by photo- or electron beam lithography

The technique of patterning of surfaces with metal-rich structures on micro- or nanoscales was developed by assembling metal nanoparticles into a thin film of polymer in a controllable way. Palladium (Pd) nanoparticles were incorporated into a thin film of poly(methyl methacrylate) (PMMA) using palladium (II) bis(acetylacetonato), Pd(acac)(2), as a precursor vaporized in a nitrogen atmosphere. Depending upon its dose, the irradiation of a PMMA film by UV light or an electron beam (EB) enhances its reducing capability against Pd(acac)(2). This dependency on dose can be used to control the formation and assembly of Pd nanoparticles. Using this technique, binary patterns consisting of metal-rich and metal-poor regions in the polymer film can be created simply by irradiating the surface of the polymer through a binary photomask. Besides the creation of binary patterns, it is also possible to create grayscale patterns where the density of Pd nanoparticles can be tuned to provide shades of gray by the use of light with continuously modulated intensity. Because the electron beam also enhances the reducing power of PMMA against Pd(acac)(2), it is thus possible to obtain highly metallized films with nanoscale pattern features. The PMMA film can be selectively removed by oxygen plasma treatment or by pyrolysis. Thus, highly metallized surfaces with binary or grayscale patterns can be obtained by selective removal of the PMMA films. The metallized regions possess relatively high resistivity against CF(4) plasma compared to the bare silicon surface; therefore, the metallized surface patterns can be transferred onto the underlying silicon substrate by CF(4) plasma treatment. Because of the nanosize effect of metal nanoparticles, the thermal treatment at 900 degrees C, which is significantly lower than the melting temperature of the bulk Pd, yields continuous metallic features by binding the assembled nanoparticles.     

Synthesis of Poly (methyl methacrylate)/Zinc Oxide Nanocomposite with Core-Shell Morphology by Atom Transfer Radical Polymerization

A method to prepare zinc oxide (ZnO) nanoparticles with a covalently bonded poly(methyl methacrylate) (PMMA) shell by surface initiated atom transfer radical polymerization (ATRP) was reported. First, the initiator for ATRP was covalently bonded onto the surface of zinc oxide nanoparticles through our novel method. Firstly, the surface of ZnO nanoparticle was treated with 3-aminopropyl triethoxysilane, a silane coupling agent, and then this functionalization nanoparticle was reacted with α-chloro phenyl acetyl chloride to prepare atom transfer radical polymerization macroinitiator. The metal-catalyzed radical polymerization of MMA with ZnOmacroinitiator was performed using a copper catalyst system to give the ZnO-based nanoparticles hybrids linking PMMA segments (poly (methyl methacrylate)/zinc oxide nanocomposite). These hybrid nanoparticles had an exceptionally good dispersability in organic solvents and were subjected to detailed characterization using FTIR, TEM and TGA and DSC analyzed.     

Preparation of poly(methyl methacrylate) grafted hydroxyapatite nanoparticles via reverse ATRP

Surface-initiated reverse atom transfer radical polymerization (reverse ATRP) technical was successfully employed to modify hydroxyapatite (HAP) nanoparticles with poly(methyl methacrylate) (PMMA). The peroxide initiator moiety for reverse ATRP was covalently attached to the HAP surface through the surface hydroxyl groups. Reverse ATRP of methyl methacrylate (MMA) from the initiator-functionalized HAP was carried out, and the end bromide groups of grafted PMMA initiated ATRP of MMA subsequently. Fourier transformation infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM) were employed to confirm the grafting and to characterize the nanoparticle structure. The grafted PMMA gave HAP nanoparticles excellent dispersibility in MMA monomer. As the amount of grafted PMMA increased, the dispersibility of surface-grafted HAP and the compressive strength of HAP/PMMA composites were improved.     

Surface modification of silica nanoparticles by UV-induced graft polymerization of methyl methacrylate

In this study we modified the surface of silica nanoparticles with methyl methacrylate by UV-induced graft polymerization. It is a surface-initiated polymerization reaction induced by ultraviolet irradiation. The resulting organic-inorganic nanocomposites were near-monodisperse and fabricated without homopolymerization of the monomer. Substantial increase in mean particle size was observed by SEM image analysis after UV-induced grafting of methyl methacrylate onto pure silica particles. FT-Raman spectroscopy and X-ray photoelectron spectroscopy studies of these materials revealed the successful grafting of methyl methacrylate onto the silica surface. The formation of a covalent bond between the grafted PMMA chains and silica surface was indicated by FT-Raman spectra. Thermogravimetric analysis of the PMMA-grafted silica particles indicated the polymer contents in good agreement with SEM photographs.     

Encapsulation of silica nanoparticles by redox-initiated graft polymerization from the surface of silica nanoparticles

This study describes a facile and versatile method for preparing polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce⁴⁺) as an oxidant and an organic reductant immobilized on the surface of silica nanoparticles. The silica nanoparticles were firstly modified by 3-aminopropyltriethoxysilane, then reacted with poly(ethylene glycol) acrylate through the Michael addition reaction, so that hydroxyl-terminated poly(ethylene glycol) (PEG) were covalently attached onto the nanoparticle surface and worked as the reductant. Poly(methyl methacrylate) (PMMA), a common hydrophobic polymer, and poly(N-isopropylacrylamide) (PNIPAAm), a thermosensitive polymer, were successfully grafted onto the surface of silica nanoparticles by ‘grafting from’ polymerization initiated by the redox reaction of Ce⁴⁺ with PEG on the silica surface in acid aqueous solutions. The polymer-encapsulated silica nanoparticles (referred to as silica@PMMA and silica@PNIPAAm, respectively) were characterized by infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. On the contrary, graft polymerization did not occur on bare silica nanoparticles. In addition, during polymerization, sediments were observed for PMMA and for PNIPAAm at a polymerization temperature above its low critical solution temperature (LCST). But the silica@PNIPAAm particles obtained at a polymerization temperature below the LCST can suspend stably in water throughout the polymerization process.     

Polymer/Ag composite microspheres produced by water-in-oil-in-water emulsion polymerization and their application for a preservative

Nanosized Ag particles were entrapped successfully in multihollow porous poly(methyl methacrylate) (PMMA) microspheres by water-in-oil-in-water emulsion polymerization. The structure of the PMMA/Ag microspheres prepared was characterized by scanning electron microscopy and X-ray powder diffraction analysis. It was found that the Ag nanoparticles were impregnated in the inner voids of the microspheres and they had a face-centered cubic structure. In the preservation test, the PMMA/Ag microspheres showed a powerful antibacterial performance, indicating that the Ag ions released effectively through the nanosized pore channel of the PMMA wall.     

Synthesis of well‐defined polymer brushes on the surface of zinc antimonate nanoparticles through surface‐initiated atom transfer radical polymerization

Zinc antimonate nanoparticles consisting of antimony and zinc oxide were surface modified in a methanol solvent medium using triethoxysilane‐based atom transfer radical polymerization (ATRP) initiating group (i.e.,) 6‐(2‐bromo‐2‐methyl) propionyloxy hexyl triethoxysilane. Successful grafting of ATRP initiator on the surface of nanoparticles was confirmed by thermogravimetric analysis that shows a significant weight loss at around 250–410 °C. Grafting of ATRP initiator onto the surface was further corroborated using Fourier transform Infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS). The surface‐initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the initiator‐fixed zinc antimonate nanoparticles in the presence of a sacrificial (free) initiator. The polymerization was preceded in a living manner in all examined cases; producing nanoparticles coated with well defined poly(methyl methacrylate) (PMMA) brushes with molecular weight in the range of 35–48K. Furthermore, PMMA‐grafted zinc antimonate nanoparticles were characterized using Thermogravimetric analysis (TGA) that exhibit significant weight loss in the temperature range of 300–410 °C confirming the formation of polymer brushes on the surface with the graft density as high as 0.26–0.27 chains/nm². The improvement in the dispersibility of PMMA‐grafted zinc antimonate nanoparticles was verified using ultraviolet‐visible spectroscopy and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Effect of magnesium dihydroxide nanoparticles on thermal degradation and flame resistance of PMMA nanocomposites

The influence of magnesium dihydroxide (MDH) nanoparticles on thermal degradation and fire behavior of poly(methyl methacrylate) (PMMA) has been investigated by thermogravimetric analysis (TGA), cone calorimeter, and pyrolysis‐combustion flow calorimeter (PCFC) tests, respectively. MDH nanoparticles with either lamellar or fibrous shape have been synthesized via a sol‐gel technique and characterized by transmission electron microscopy (TEM) and X‐ray diffraction analysis. PMMA–MDH nanocomposites have been prepared by melt blending the recovered MDH nanoparticles within PMMA at different loadings (5, 10, and 20 wt% MDH). According to TGA results, the incorporation of lamellar or fibrous MDH nanoparticles into PMMA leads to a significant improvement in PMMA thermal stability, both under air and inert atmosphere. The results obtained by PCFC and cone calorimeter tests show an important decrease in the peak of heat release rate (pHRR) concomitant with charring during the combustion. Lamellar MDH nanoparticles were found to be more efficient than fibrous MDH nanoparticles. Copyright © 2010 John Wiley & Sons, Ltd.     

Properties of matrix-grafted multi-walled carbon nanotube/poly(methyl methacrylate) nanocomposites synthesized by in situ reversible addition-fragmentation chain transfer polymerization

Multi-walled carbon nanotubes (MWCNT)/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by the in situ reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in the presence of MWCNTs, at which the bulk polymer was grafted onto the surface of nanotubes through the ??grafting through?? strategy. For this purpose, MWCNTs were formerly functionalized with polymerizable MMA groups. MMA and PMMA-grafted MWCNTs were characterized by Fourier-transform infrared spectroscopy, Raman, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Dissolution of nanotubes was examined in chloroform solvent and studied by UV?Cvis spectroscopy. Thermogravimetric and degradation behavior of prepared nanocomposites was investigated by TGA. MWCNTs had a noticeable boosting effect on the thermal stability of nanocomposites. TGA thermograms showed a two-step weight loss pattern for the degradation of MWCNT-PMMA/PMMA nanocomposites which is contrast with neat PMMA. Introduction of MWCNTs also improved the dynamic mechanical behavior and electrical conductivity of nanocomposites. TEM micrograph of nanocomposite revealed that the applied methods for functionalization of nanotubes and in situ synthesis of nanocomposites were comparatively successful in dispersing the MWCNTs in PMMA matrix.     

The effect of ionising radiation on poly(methyl methacrylate) used in intraocular lenses

Gamma radiation is increasingly being used to sterilise intraocular lenses (IOLs) made from poly(methyl methacrylate) (PMMA). In this study, samples of PMMA used in the fabrication of IOLs were exposed to irradiation doses typically used for their sterilisation. The effect of this treatment on the polymer was analysed by size-exclusion chromatography (SEC), UV-visible and infrared spectroscopy and scanning electron microscopy (SEM). The PMMA was found to have undergone chain scission, decarboxylation and colour change following the irradiation.     

Synthesis of high molecular weight poly(methyl methacrylate) microspheres by suspension polymerization in the presence of silver nanoparticles

To prepare high molecular weight (HMW) poly(methyl methacrylate) (PMMA)/silver microspheres, methyl methacrylate was suspension-polymerized in the presence of silver nanoparticles using a low-temperature initiator at different conditions. The rate of conversion was increased with increasing initiator concentration. In the case of adding silver nanoparticles, the rate of polymerization decreased slightly. High monomer conversion (about 95%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres with various viscosity-average degree of polymerization (6,000–37,000) were prepared.     

Methyl methacrylate oligomerically-modified clay and its poly(methyl methacrylate) nanocomposites

A methyl methacrylate oligomerically-modified clay was used to prepare poly(methyl methacrylate) clay nanocomposites by melt blending and the effect of the clay loading level on the modified clay and corresponding nanocomposite was studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed intercalated/delaminated morphology with good nanodispersion. The compatibility between the methylacrylate-subsituted clay and poly(methyl methacrylate) (PMMA) are greatly improved compared to other oligomerically-modified clays.     

In situ Synthesis of Poly(methyl methacrylate)/Graphene Oxide Nanocomposites Using Thermal-initiated and Graphene Oxide-initiated Polymerization

A facile and cost-effective method to prepare poly(methyl methacrylate) (PMMA)/graphene oxide (GO) nanocomposites was developed by in situ polymerization. By using thermal-initiated and GO-initiated polymerization of methyl methacrylate (MMA), no extra radical initiator was added during the reaction. Without any pre-functionalization of GO, PMMA chains were covalently bonded to its surface, which was confirmed by Fourier-transform infrared, atomic force microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy investigations. TGA analysis showed that the mass ratio of grafted PMMA and GO was as high as 1.7. Transmission electron microscopy and X-ray powder diffraction investigations demonstrated that the grafting of PMMA chains to GO surfaces resulted in homogeneous dispersion of GO sheets in PMMA matrix, which led to a commendable performance on its mechanical and thermal properties. Dynamic mechanical analysis showed that, at a loading level of just 0.5 wt% for the nanocomposites, the storage modulus of the nanocomposites was improved 14%, and the glass transition temperature was increased 12°C in comparison with that of neat PMMA. Thermogravimetric analysis showed that the onset degradation temperature of the nanocomposites was increased 13°C with a GO content of 0.25 wt%.     

Preparation of PMMA/acid-modified chitosan core-shell nanoparticles and their potential as gene carriers

The core-shell nanoparticles consisting of poly(methyl methacrylate) (PMMA) cores surrounded by various acid-modified chitosan shells were synthesized using a surfactant-free emulsion copolymerization, induced by a tert-butylhydroperoxide (TBHP) solution. Methyl methacrylate (MMA) was grafted onto four acid-modified chitosans (hydrochloric, lactic, aspartic, and glutamic acids) with MMA conversions up to 64%. The prepared nanoparticles had diameter ranging from 100 to 300 nm characterized by atomic force microscopy and displayed highly positive surface charges up to +77 mV. Transmission electron microscopic images clearly revealed well-defined core-shell morphology of the nanoparticles where PMMA cores were coated with acid-modified chitosan shells. The effect of acid-modified chitosans on particle size, intensity of surface charge, morphology, and thermal stability were determined systematically. The plasmid DNA/nanoparticles complexes were investigated with ζ-potential measurement. The results suggested that these nanoparticles can effectively complex with plasmid DNAs via electrostatic interaction and could be used as gene carriers.

Synthesis and Characterization of Poly(methyl methacrylate)-b-Polystyrene/TiO2 Nanocomposites Via Reversible Addition-Fragmentation Chain Transfer Polymerization

A diblock copolymer, poly(methyl methacrylate)-b-polystyrene (PMMA-b-PS), was grafted onto the surface of nano-titania (nano-TiO₂) successfully via reversible addition-fragmentation chain transfer (RAFT) polymerization. The surface of TiO₂ nanoparticles was modified initially by attaching dithioester groups to the surface using silane coupling agent 3-(chloropropyl)triethoxy silane and sodium ethyl xanthate. The polymerization of methyl methacrylate and styrene were then initiated and propagated on the TiO₂ surface by RAFT polymerization. The resulting composite nanoparticles were characterized by means of XPS, FT-IR, ¹H NMR and TGA. The results confirmed the successful grafting of poly(methyl methacrylate) (PMMA) and diblock copolymer chains onto the surface of TiO₂. The amount of PMMA grafted onto the TiO₂ surface increased with the polymerization time. Moreover, the kinetic studies revealed that the ln([M]₀/[M]), where [M]₀ is the initial and [M] is the time dependent monomer concentrations, increased linearly with the polymerization time, indicating the living characteristics of the RAFT polymerization.