Phase continuity in polystyrene–nylon 6,10 graft copolymers

Using a modified interfacial polymerization route, a graft copolymer of nylon 6,10 and polystyrene was prepared. First, an aqueous suspension of styrene monomer was encapsulated with nylon 6,10, followed by polymerization of the styrene to form the graft copolymer. When the material was subsequently molded below the crystalline melting point of nylon 6,10 (220°C), modulus–temperature behavior intermediate between polystyrene and nylon 6,10 was observed. However, when this graft copolymer was molded above the melting point of nylon 6,10, behavior more like pure polystyrene was observed. Phase contrast microscopy revealed that material molded below 220°C showed a continuous cellular-phase structure of about 30 microns in diameter, the interior of the cells being composed of polystyrene and the cell walls being composed of nylon 6,10. Phase inversion phenomenon was observed in the graft copolymer as the molding temperature was raised above 220°C. The nylon 6,10 phase became discontinuous, small globules being formed. This behavior is analogous to spheroidization in steel. It is thought that molten nylon 6,10 spheroidizes to attain a lower surface-energy state.     

Defocus electron microscopy of multiphase polymers: use and misuse

Application of defocus microscopy to the imaging of multiphase polymers is investigated. Theoretical image contrast of ideally phase separated, model objects is predicted by application of the transfer theory of imaging. The calculations are in good agreement with observed images of a polypropylene film. Easy recognition of the cross-hatched structure of polypropylene, however, necessitates the use of very high defocus values. Application of this defocus technique to more complex systems causes problems. Defocused images of a polyurethane film are found to be indistinguishable from those of a carbon film or an amorphous polystyrene film, i.e. the image is dominated by the spatially filtered noise structure. It is suggested that previous electron-micrographs of domain structures of polyurethanes have been misinterpreted.     

Phasenkontrast‐Rasterkraftmikroskopie für die Charakterisierung der Verteilung von Nanopartikeln in Verbundwerkstoffen

Atomic Force Microscopy (AFM) is a versatile tool for analyzing particle and disperse systems. The method of phase contrast imaging as an AFM modality is investigated for applicability for analyzing the state of dispersion. It is shown how homogeneity as well as state of agglomeration can be examined for nanoparticles in a polymer or wax matrix. A method to achieve quantitative information from the high contrast images obtained by mathematical tools is introduced.     

Polystyrene-graft-acrylic acid as compatibilizer of polystyrene/nylon 6,6 blends

Preliminary investigations to study the feasibility of using polystyrene grafted with acrylic acid to blend polystyrene (PS) and nylon 6,6 (N66) have been done. The graft copolymer (PS-g-AA) was synthesized by reacting polystyrene with acrylic acid in the presence of a free radical initiator using the solid phase graft copolymerization technique. Binary blends of N66/PS and N66/PS-g-AA were synthesized by melt mixing. The formation of a (PS-g-AA)-co-N66 copolymer during the blend preparation has been desired. The blend morphologies were observed by scanning electron microscopy (SEM). Significant reductions in the domain sizes of the dispersed minor phase were observed when PS-g-AA instead of PS was incorporated into the blend. The tensile properties of the blends were investigated. The belnds containing PS-g-AA were found to be stiffer (higher modulus) and stronger (higher tensile strength) as compared to the blends containing PS. These results are due to the better miscibility and adhesion between nylon 6,6 and the graft copolymer. The results of the rheological measurement of these blends further supports the above result and also indicates an increase in the molecular weight distribution (MWD) of the blend when polystyrene was replaced by the graft copolymer. This increase in the MWD of the compatibilized blend can be attributed to above assumed copolymer formation between the graft copolymer and nylon 6,6 due to the reaction between the carbonyl group of the acrylic acid and the amide and the terminal amine groups of nylon 6,6.     

Well-defined core-shell structures based on silsesquioxane microgels: Grafting of polystyrene via ATRP and product characterization

Silsesquioxane microgel nanoparticles characterized by low diameters (below 30 nm) and reduced polydispersity can be produced in an acid-catalyzed sol-gel process in an aqueous microemulsion. Suitable surface modification of such structures leads to macroinitiators for atom-transfer radical polymerization (ATRP). This polymerization method was applied in order to graft polystyrene chains onto the surface of the microgels. Well-defined structures exhibiting a core-shell architecture were produced with the M_w of grafted polymers ranging from 8.5 to about 30 kg/mol. The products were extensively characterized with light scattering, X-ray scattering, thermal analysis (TGA/DSC) and microscopy (TEM/SEM) to obtain information on parameters characterizing polystyrene brush. Polymer-grafted nanoparticles will be used for the modification of homopolymer and block copolymer matrices.     

聚苯乙烯大单体/丙烯酸辛酯规整接枝共聚物的结构、性能与增容作用

用傅里叶变换红外光谱、透射电子显微镜和差示扫描量热仪表征了聚苯乙烯大单体和丙烯酸辛酯规整接枝共聚物(POA-g-PS)的结构,测定了其物理机械性能,并研究了POA-g-PS作为聚苯乙烯/丙烯酸酯橡胶体系的共混增容剂时,共混物组成、接枝物用量及接枝物组成对共混物物理机械性能的影响。结果表明,POA-g-PS属于两相态,存在微观相分离结构;当聚苯乙烯大单体的质量分数在40%左右时,POA-g-PS是一种具有较大拉伸强度、较大扯断伸长率及较小永久变形的热塑性弹性体;扫描电镜和差示扫描量热分析表明接枝共聚物促进了聚苯乙烯/丙烯酸酯橡胶共混体系的互容,起到了增容剂的作用。     

A comparison of atomic force microscope friction and phase imaging for the characterization of an immiscible polystyrene/poly(methyl methacrylate) blend film

Three different forms of atomic force microscope (AFM) measurement, topography, friction force and phase imaging, have been used to investigate the surface morphology and local composition of an immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend film. This sample forms discrete, micron-size domains in a continuous matrix, which is attributed to the segregation of PMMA in PS. When the samples were imaged in air, contrast in friction and phase images was caused by variations in sample topography only. When the samples were imaged under water, however, both friction and phase imaging yielded non-topographic contrast between domains. We ascribe the contrast in both of these imaging modes to preferential softening of the hydrophilic, PMMA-rich domains and to stronger tip-sample adhesive forces, highlighting the AFM's utility for probing local elastic properties and for compositional mapping of soft polymer samples.     

Enhanced nanoflow behaviors of polymer melts using dispersed nanoparticles and ultrasonic vibration

In the micro/nano fabrication of polymer nanostructures, a key factor is the favorable nanoflow behavior of polymer melts. Compared with the fluidic hydrodynamics of simple liquids through micro- or macrochannels, the nanoflow behavior of polymer melts, however, is affected much more by nanoscale effects and surface interactions. Therefore, achieving a favorable nanoflow of polymer melts in nanochannels is the key to fabricate high quality polymer nanoproducts. In this paper, the improved nanoflow behaviors of polystyrene melts in ordered porous alumina templates with the addition of nanoparticles and ultrasonic vibration were reported for the first time. Compared with bulk polystyrene (PS), the nanoflow rate of PS melts was enhanced when nanoparticles, such as surface-modified nano-silica (nano-SiO(2)) or β-cyclodextrin (β-CD), were added in a dispersed phase into a polystyrene matrix due to the decrease of the melts' viscosity caused by interactions between nanoparticles and PS segments. The enhancement action of β-CD was observed to be more significant than that of nano-SiO(2) based on the adsorption and the supramolecular self-assembly interactions between PS segments and β-CD. The enhanced nanoflow rate has shown to be more pronounced under ultrasonic vibration than those of the static condition and the low frequency vibration attributed to the synergetic effects of mechanical vibration and ultrasonic oscillation. The nanoflow rate of polymer melts increases with the gradual increase of vibration frequency. The optimal nanoflow behavior can be obtained by simultaneously adding β-CD as dispersed phase into PS matrix and applying ultrasonic vibration in one nanoflow system. These new findings will help the preparation of polymer-based functional nanocomposites, ultrasonic vibration-assisted nanofluidics, and micro/nano injection molding etc.     

Theranostic magnetic nanoparticles

Early detection and treatment of disease is the most important component of a favorable prognosis. Biomedical researchers have thus invested tremendous effort in improving imaging techniques and treatment methods. Over the past decade, concepts and tools derived from nanotechnology have been applied to overcome the problems of conventional techniques for advanced diagnosis and therapy. In particular, advances in nanoparticle technology have created new paradigms for theranostics, which is defined as the combination of therapeutic and diagnostic agents within a single platform. In this Account, we examine the potential advantages and opportunities afforded by magnetic nanoparticles as platform materials for theranostics. We begin with a brief overview of relevant magnetic parameters, such as saturation magnetization, coercivity, and magnetocrystalline anisotropy. Understanding the interplay of these parameters is critical for optimizing magnetic characteristics needed for effective imaging and therapeutics, which include magnetic resonance imaging (MRI) relaxivity, heat emission, and attractive forces. We then discuss approaches to constructing an MRI nanoparticle contrast agent with high sensitivity. We further introduce a new design concept for a fault-free contrast agent, which is a T1 and T2 dual mode hybrid. Important capabilities of magnetic nanoparticles are the external controllability of magnetic heat generation and magnetic attractive forces for the transportation and movement of biological objects. We show that these functions can be utilized not only for therapeutic hyperthermia of cancer but also for controlled release of cancer drugs through the application of an external magnetic field. Additionally, the use of magnetic nanoparticles to drive mechanical forces is demonstrated to be useful for molecular-level cell signaling and for controlling the ultimate fate of the cell. Finally, we show that targeted imaging and therapy are made possible by attaching a variety of imaging and therapeutic components. These added components include therapeutic genes (small interfering RNA, or siRNA), cancer-specific ligands, and optical reporting dyes. The wide range of accessible features of magnetic nanoparticles underscores their potential as the most promising platform material available for theranostics.     

Monodisperse magnetic nanoparticles for biomedical applications

Magnetic nanoparticles that are superparamagnetic with high saturation moment have great potential for biomedical applications. Solution‐phase syntheses have recently been applied to make various kinds of monodisperse magnetic nanoparticles with standard deviation in diameter of less than 10%. However, the surface of these nanoparticles is coated with a layer of hydrocarbon molecules due to the use of lipid‐like carboxylic acid and amine in the syntheses. Surface functionalization leads to the formation of water‐soluble nanoparticles that can be further modified with various biomolecules. Such functionalization has brought about several series of monodisperse magnetic nanoparticle systems that have shown promising applications in protein or DNA separation, detection and magnetic resonance imaging contrast enhancement. The goal of this mini review is to summarize the recent progress in the synthesis and surface modification of monodisperse magnetic nanoparticles and their applications in biomedicine. Copyright © 2007 Society of Chemical Industry     

Sustained release properties of arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers

The release kinetics of small molecules from dendritic graft copolymer micelles incorporating an arborescent polystyrene (PS) core and a poly(2-vinylpyridine) (P2VP) shell were investigated in dilute HCl solutions by fluorescence and UV spectroscopies. The redistribution of pyrene and perylene among arborescent micelles was studied by the fluorescence resonance energy transfer (FRET) technique, and was characterized by an initial burst in exchange followed by gradual equilibration of the probes. Fluorescence quenching experiments demonstrated that the diffusion coefficient of pyrene increased for copolymer micelles of higher generations, suggesting a more porous shell structure for the higher generation arborescent PS-g-P2VP copolymers. In vitro release tests for indomethacin and lidocaine monitored by UV spectroscopy showed that sustained release characteristics were achieved, the release rate being higher for lidocaine due to its higher water solubility at low pH. The release rate of indomethacin increased for lower generation micelles and for higher micelle loadings, in agreement with a diffusion-controlled release mechanism. An increasing fraction of the indomethacin molecules loaded in the micelles remained trapped for higher generation copolymers. The diffusion coefficient and the release rate of indomethacin were calculated by fitting the solution of Fick's second law of diffusion to the experimental data. While the initial release rate decreased for higher generations, the trends observed for the diffusion coefficients were similar to those determined for pyrene in the fluorescence quenching experiments. This result is again consistent with a more diffuse shell structure for higher generation micelles, possibly due to the enhanced electrostatic repulsions between the charged P2VP chains.     

Ordering of block copolymer/nanoparticle composite thin films

The ordering behavior of polymer nanocomposites composed of gold nanoparticles confined in the polystyrene (PS) domains of PS based block copolymers was investigated. The results reveal that the self‐assembly of nanoparticles in the PS domains improved the ordering of microdomains. This is attributed to the presence of nanoparticles that reduced the degree of segregation of the system, causing slow phase separation. This facilitates the packing of the cylindrical microdomains, leading to a well‐ordered structure of the composite. When particles were incorporated into the major domains of cylindrically ordered block copolymer, the connectivity of the domains allowed particles to move to the top of the film to gain additional entropy of the system. In contrast, when particles were organized in parallel cylinders in the block copolymer, they were confined in the cylinders which prevented them from diffusing in the depth direction. The aggregation of nanoparticles was amplified when the composite was annealed in air. We believe that the results from this study will enable more understanding of the effects of nanoparticles on the ordering of block copolymer/nanoparticle composite thin films and will provide a tool in the fabrication of composite thin films. Copyright © 2012 Society of Chemical Industry     

Enhancing the fraction of grafted polystyrene on silica hybrid nanoparticles

Polymer-grafted inorganic nanoparticles are being developed for a diverse array of applications, ranging from drug delivery to multifunctional composites. In many instances, performance of these core-shell hybrids is limited by relatively broad distributions of size and composition, as well as the presence of impurities, such as unattached polymer chains. Herein, further synthetic improvements, and associated characterization techniques, to enhance the fraction of the grafted polystyrene shell on silica hybrid nanoparticles are discussed. We found that during surface-initiated atom transfer radical polymerization (SI-ATRP) from the silica nanoparticles, thermal self-initiation of styrene produces unattached polymer chains. Size exclusion chromatography afforded a facile approach to quantify the mass of the unattached polymer, and provide a substantial refinement to estimates of chain graft density beyond traditionally-used approaches, such as thermogravimetry. This fraction of unattached polymer is still present even after post-polymerization work-up via precipitation and re-dissolution. Removal necessitates additional procedures, such as high speed centrifugation. Selection of a lower polymerization temperature, in concert with a more reactive Cu complex, significantly reduces the amount of unattached polystyrene impurity. The improved polymerization conditions and post-polymerization purification provide more refined polystyrene-grafted silica nanoparticles to clarify structure-property relationships of these core-shell hybrids.     

Ionomers made from copolymers with uniform grafts

Summary Carboxylic acid-containing graft copolymers with uniform polystyrene grafts were synthesized by copolymerization of methacrylate-terminated polystyrene macromers, acrylic acid and butyl scrylate. The graft copolymers were neutralized with metal ions in solution or in melt to form ionomers, which were characterized by IR, TEM and dynamic mechanical analysis. TEM photographs showed that there appeared three phases in the ionomers, namely polystyrene domains, ion clusters and continueous phase of polybutyl acrylate, while dynamic mechanical analysis indicated the phase separation of polystyrene and ion-containing polyacrylate.     

Electron holography and AFM studies on styrenic block copolymers and a high impact polystyrene

Many of the artifacts of conventional electron microscopy can be avoided if the unstained polymers are studied by electron holography and atomic force microscopy (AFM). Holograms of thin sections (50–70 nm) of organic block copolymers were recorded, and the corresponding phase images were reconstructed. In this way, typical structures such as lamellae and cylinders could be imaged without any staining. In addition, we successfully recorded holograms and performed Lorentz microscopy of an impact‐modified polystyrene (high‐impact polystyrene). The results were compared with the tapping mode AFM phase images. Electron holography and AFM have been demonstrated as suitable tools to image unstained heterogeneous polymers, leading to the understanding of their structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1573–1583, 2005     

Magnetic Iron Oxide Nanoparticles for Multimodal Imaging and Therapy of Cancer

Superparamagnetic iron oxide nanoparticles (SPION) have emerged as an MRI contrast agent for tumor imaging due to their efficacy and safety. Their utility has been proven in clinical applications with a series of marketed SPION-based contrast agents. Extensive research has been performed to study various strategies that could improve SPION by tailoring the surface chemistry and by applying additional therapeutic functionality. Research into the dual-modal contrast uses of SPION has developed because these applications can save time and effort by reducing the number of imaging sessions. In addition to multimodal strategies, efforts have been made to develop multifunctional nanoparticles that carry both diagnostic and therapeutic cargos specifically for cancer. This review provides an overview of recent advances in multimodality imaging agents and focuses on iron oxide based nanoparticles and their theranostic applications for cancer. Furthermore, we discuss the physiochemical properties and compare different synthesis methods of SPION for the development of multimodal contrast agents.     

Facile preparation of curved polymer composite nanosheets

A facile no-template approach for fabricating curved polystyrene (PS) nanosheets by miniemulsion polymerization technique was developed. Two essences of the high hydrophobicity of oil phase and the existence of cross-linking comonomer were found to ensure the stable curved sheet-like morphology. Here, when choosing tetradecane as the hydrophobic oil phase and divinylbenzene as cross-linker, the curved PS nanosheets with stable structure were obtained. Furthermore, after introducing functional groups by sulfonation reaction, these curved PS nanosheets can be used as a general template for preparing curved sheet-like inorganic/organic nanocomposites with broadly varied inorganic ingredients, such as metal Ag nanoparticles, inorganic titania, silica, etc. Otherwise, when calcining or carbonizing these inorganic/organic nanocomposites under air or nitrogen, novel mesoporous or microporous pure inorganic nanomaterials with curved sheet-like morphology were obtained conveniently further.     

The production of a new partially biodegradable starch plastic by reactive extrusion

The grafting of polystyrene onto dissolved starch in a twin screw extruder has been studied. This copolymerization was initiated using the thermal initiators benzoyl peroxide and K₂S₂O₈. As end product a mixture containing polystyrene‐grafted starch, homopolymer of polystyrene and starch was obtained. Parameters like screw rotation rate, fully filled length of the extruder, wall temperature and throughput have been varied in order to obtain information about their influence on conversion, graft percentages and molecular weight of the materials formed. To increase the amount of graft points, maleic acid anhydride (MAH) was added resulting in an increased grafting of polystyrene onto starch. Graft percentages of 60% could be achieved. The total conversion of styrene could be controlled by adjusting extruder parameters like barrel temperature, fully filled length and initiator type. Conversions of 95% were found. Molecular weights of the polystyrene formed could be controlled by adding a chain transfer agent (dodecylmercaptan) to the styrene phase. In this way the molecular weight (M_n) of the styrenic part could be varied from 20,000 to 140,000. The experiments with the chain transfer agent showed that the grafting of polystyrene onto starch is a process occurring at the interface between the dissolved starch and the styrene phase.     

Synergistically integrated nanoparticles as multimodal probes for nanobiotechnology

Current biomedical imaging techniques including magnetic resonance imaging (MRI), positron emission tomography (PET), and computed X-ray tomography (CT) are vital in the diagnosis of various diseases. Each imaging modality has its own merits and disadvantages, and a single technique does not possess all the required capabilities for comprehensive imaging. Therefore, multimodal imaging methods are quickly becoming important tools for state-of-the-art biomedical research and clinical diagnostics and therapeutics. In this Account, we will discuss synergistically integrated nanoparticle probes, which will be an essential tool in multimodal imaging technology. When inorganic nanoparticles are introduced into biological systems, their extremely small size and their exceptional physical and chemical properties make them useful probes for biological diagnostics. Nanoparticle probes can endow imaging techniques with enhanced signal sensitivity, better spatial resolution, and the ability to relay information about biological systems at the molecular and cellular levels. Simple magnetic nanoparticles function as MRI contrast enhancement probes. These magnetic nanoparticles can then serve as a core platform for the addition of other functional moieties including fluorescence tags, radionuclides, and other biomolecules for multimodal imaging, gene delivery, and cellular trafficking. For example, MRI-optical dual-modal probes composed of a fluorescent dye-doped silica (DySiO(2)) core surrounded by magnetic nanoparticles can macroscopically detect neuroblastoma cancer cells via MRI along with subcellular information via fluorescence imaging. Magnetic nanoparticles can also be coupled to radionuclides ((124)I) to construct MRI-PET dual-modal probes. Such probes can accurately detect lymph nodes (LNs), which are critical for assessing cancer metastasis. In vivo MRI/PET images can clearly identify small (approximately 3 mm) LNs along with precise anatomical information. Systems using multicomponent nanoparticles modified with biomolecules can also monitor gene expression and other markers in cell therapeutics studies. We have used hybrid stem cell-magnetic nanoparticle probes with MRI to monitor in vivo stem cell trafficking. MRI with hybrid probes of magnetic nanoparticles and adenovirus can detect target cells and can monitor gene delivery and the expression of green fluorescent proteins optically. Each component of such multimodal probes complements the other modalities, and their synergistic materials properties ultimately provide more accurate information in in vitro and in vivo biological systems.     

Arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers as unimolecular micelles: Solubilization studies

Solubilization of various polycyclic aromatic hydrocarbon (PAH) probes by arborescent polystyrene-graft-poly(2-vinylpyridine) unimolecular micelles of different structures in aqueous solutions was investigated by UV and fluorescence spectroscopies. The micelle-water partition coefficient K_w and the solubilization capacity κ^G both increased with the polystyrene content of the copolymers for all probes, but the increase was less significant for the less hydrophobic probes. The K_w values obtained correlated well with the octanol-water partition coefficient and the boiling point of the more hydrophobic probe molecules, but no clear trend was observed for κ^G. The results obtained suggest that highly hydrophobic probes are solubilized mainly in the non-polar polystyrene core. A significant portion of the least hydrophobic probes resides in the ionic shell, while probes of intermediate polarity appear to remain in the palisade (interfacial) region. The branching functionality of the micelles played an important role in the solubilization process: for copolymers of similar composition, the solubilization capacity and rate were lower for higher generations, presumably due to the more rigid structure of the molecules. The results obtained show that arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers can be designed to solubilize compounds of different polarities at controllable rates.