Thin-film solid-state proton NMR measurements using a synthetic mica substrate: Polymer blends

Solid-state proton nuclear magnetic resonance (NMR) measurements are performed successfully on polymer blend thin films through the use of synthetic mica as a substrate. When used as a substrate, synthetic fluorophlogopite mica with its proton-free, diamagnetic character, allows for adequate measurement sensitivity while minimally perturbing the proton thin-film spectra, especially relative to more commonly available natural micas. Specifically, we use multiple-pulse techniques in the presence of magic-angle spinning to measure the degree of mixing in two different polymer blend thin films, polystyrene/poly(xylylene ether) and poly(1-methyladamantyl methacrylate) (PMAdMA)/triphenylsulfonium perfluorobutanesulfonate (TPS-PFBS), spin-coated onto mica substrates. Our earlier studies had focused on bulk systems where NMR signals are stronger, but may not be representative of thin films of the same systems that are relevant to many applications such as photoresist formulations in the electronics industry. The superiority of synthetic over natural paramagnetic mica is demonstrated by the maintenance of resolution and spinning sideband intensities (relative to bulk samples) for the synthetic mica samples. In contrast, degraded resolution and large spinning sidebands are shown to typify spectra of the natural mica samples. This approach can be applied to many other proton measurements of solid thin films, thereby greatly extending the types of systems to be investigated. Magnetic susceptibility measurements are also reported for all micas used.     

Grafting of polymers onto graphene oxide by cationic and anionic polymerization initiated by the surface-initiating groups

The grafting of polymers onto graphene oxide (GO) was achieved by two process: (1) cationic polymerization initiated by carboxyl (COOH) groups on GO and (2) anionic alternating copolymerization of epoxides with cyclic acid anhydrides initiated by potassium carboxylate (COOK) groups on GO. The cationic polymerizations of isobutyl vinyl ether and N-vinylcarbazole were successfully initiated by COOH groups on GO to give the corresponding polymer-grafted GO. The cationic polymerization was considered to be initiated by proton addition from COOH groups to monomer and propagation of polymer cation proceeds with carboxylate anion as a counter ion. It was found that the corresponding polymer was successfully grafted onto GO based on the termination reaction of growing polymer cation and surface counter carboxylate anion. On the other hand, the anionic ring-opening alternating copolymerization of epoxide and cyclic acid anhydrides were also initiated by COOK groups on GO, which were previously introduced onto GO by the neutralization of COOH groups with KOH. During the anionic ring-opening copolymerization of styrene oxide (SO) with phthalic anhydride (PAn) and maleic anhydride (MAn), the corresponding polyesters, poly(SO-alt-PAn) and poly(SO-alt-MAn), were successfully grafted onto GO, based on the propagation of the polyesters from COOK groups. The grafting of polymers onto GO during the above cationic and anionic polymerizations was confirmed by thermal decomposition gas chromatogram/mass spectrum. The untreated GO in THF was immediately precipitated within 15 min. On the contrary, these polymer-grafted GOs gave stable dispersions in THF and no precipitation of polymer-grafted GOs was observed even after one week.     

High CEC generation and surface modification in mica and vermiculite minerals

Montmorillonite layered silicate has been commonly used to reinforce polymer matrices. Due to its swelling in water, organic modification of the mineral surface is easily achieved which makes the surface compatible with polymers. Other minerals like mica and vermiculite though can also lead to high aspect ratio platelets in nanocomposites, but they do not swell in water owing to much stronger electrostatic forces of attraction holding their platelets together (layer charge density >0.5?eq?·?mol^?1 in comparison with 0.25–0.5?eq?·?mol^?1 for montmorillonite). In current study, milling, delamination and cation exchange processing of mica and vermiculite minerals has been reported to explore their potential as reinforcement materials. Wet grinding and subsequent sieving of the coarse minerals led to fine-sized particles suitable to perform chemical delamination in water. The delamination process resulted in Li-mica and Na-vermiculite with enhanced access to the interlayer cations, thus, higher CEC. Successful surface modification of the delaminated minerals with alkyl ammonium ions could be achieved which resulted in significant enhancements in their basal plane spacing. Peak degradation temperatures of 260°C were measured for C18 and 2C18 modified vermiculite, whereas 300°C and 275°C were observed respectively for C18 and 2C18 modified mica minerals which make them suitable for compounding with polymers at high temperature.     

Excimer UV lamp irradiation induced grafting on synthetic polymers

Surface modifications on polyethyleneterephthalate (PET) films following excimer UV lamp irradiation induced grafting were studied. Characteristics of the modifications depending on the conditions during the irradiation were analysed using contact-angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). Depending on the conditions during the irradiation different surface modifications were obtained, which can generally be classified regarding the hydrophilic or hydrophobic characteristics of the resulting surface. It is shown that not every substance that meets the general demands will be grafted on synthetic polymers using excimer UV radiation. Examples of agents that can simply be grafted onto polymer surfaces and those that undergo further crosslinking, building up thin films are listed. Agents used for grafting on polymers are 1,5-hexadiene, perfluoro-4-methyl-pent-2-ene, polyethyleneglycol 200, monosilane and polyethylene. The transferability of the effects achieved to substrates such as polyparaphenylene terephthalamide or polymetaphenylene isophthalamide is shown. Received: 23 June 2000 / Accepted: 28 June 2000 / Published online: 5 October 2000     

Silane-modified polymers as interphases in glass-fibre-reinforced composites: 2. Grafting and crosslinking of interphase materials

_—This paper presents an interphase engineering technique suitable for grafting silane-modified polymers onto glass fibres to be used in composites with enhanced impact tolerance. The silane-modified polymers include ethylene polymers grafted with γ-methacryloxypropyltrimethoxysilane (MPS) and a copolymer of butyl acrylate (BuA) and MPS. The grafting of functionalized interphase materials onto glass fibres is performed in solution. By changing the concentrations of the solutions, different amounts of polymer can be deposited on the fibres. Water crosslinking of the polymer gives the possibility of producing stabilised interfacial polymer coatings over a range of thicknesses. It is concluded that acidic conditions (1) promote the grafting of silane-modified polymers on glass fibres and (2) for a given reaction time, increase the amount of crosslinked polymer in the interphase, i.e. yield more stable interphases. It is also likely that preserving acidic conditions at the fibre/polymer interface is important for maintaining bonding across the interface. It is shown that polystyrene/glass-fibre composites having SEBS at the interface are promising candidates for high-impact-tolerance composites.     

Silane-modified polymers as interphases in glass-fibre-reinforced composites: 1. Synthesis and characterisation of alkoxy-silane functionalized polymers

This paper presents techniques for the functionalization of polymer materials with alkoxy-silane groups. Alkoxy-silane groups are key intermediates in bonding organic materials onto glass-fibre surfaces. Two reaction routes are described: (1) Chain copolymerization of butyl acrylate (BuA) and γ-methacryloxypropyltrimethoxy-silane (MPS) and (2) grafting of MPS onto polyethylene (PE) and poly(styrene-block-ethylene-co-1-butene-block-styrene) (SEBS). It is concluded that chain copolymerization is the superior route since it gives almost unlimited possibilities of adjusting the degree of alkoxy-silane functionality. The paper also demonstrates the advantage of performing graft copolymerization in the melt instead of in solution. Solution grafting is of low efficiency and is probably directed to chains having reactive sites, e.g. branch points. It is proposed that the primary cause is the lower temperatures used in solution grafting in comparison to the melt reaction.     

用于质子交换膜材料的侧链型磺化聚芳醚酮砜的光谱分析

采用直接缩聚的方法,通过调整氨基单体用量,合成出了系列带有不同氨基含量的聚芳醚酮砜(Am-PAEKS)聚合物,在聚合物侧链上进行后磺化接枝制备出了系列不同磺化度的侧链型磺化聚芳醚酮砜(S-SPAEKS),并且通过调整磺酸基团含量来控制聚合物的磺化度。通过红外光谱(FTIR)和氢核磁谱(1HNMR),对所合成的单体及其聚合物的结构进行了表征,S-SPAEKS红外光谱在1 239和1 060 cm-1处出现了磺酸基团中OSO的特征吸收峰,氢核磁谱中1.64 ppm处出现了处于烷基链中间位置的两个氢(—CH₂—CH₂—)化学位移,证明得到了S-SPAEKS聚合物。经热失重分析发现,聚合物中磺酸基团的脱落温度都高于240 ℃,聚合物主链降解温度都高于450 ℃。研究表明,该系列聚合物具有良好的热性能,可以用作质子交换膜材料。     

Surface modification of calcium carbonate: radical graft polymerization of vinyl monomers onto calcium carbonate surface initiated by azo groups introduced onto the surface

—The preparation of calcium carbonate modified by 12-hydroxystearate groups and the grafting of polymers onto the surface by the polymerization of vinyl monomers initiated by azo groups introduced onto the surface were investigated. The preparation of calcium carbonate modified by 12-hydroxystearate was achieved by the reaction of calcium chloride with sodium carbonate containing a small amount of sodium 12-hydroxystearate. The introduction of azo groups onto calcium carbonate was successfully achieved by the direct condensation of the carboxyl group of 4,4'-azobis(4-cyanopentanoic acid) with 12-hydroxystearate groups on the modified calcium carbonate using N,N'-dicyclohexylcarbodiimide as a condensing agent. It was found that the radical polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and N-vinylcarbazole (NVC), was initiated by azo groups introduced onto the surface, and the corresponding polymers were grafted onto the surface based on the propagation of polymer from the surface: the percentage of grafting of polyMMA, polystyrene, and polyNVC reached 5.7, 9.5 and 3.5%, respectively, at 70°C. The percentage of grafting was found to decrease with decreasing monomer concentration. The wettability of calcium carbonate surface was found to turn from hydrophilic to hydrophobic by the grafting of polymers.     

Performance of a polarizer using synthetic mica crystal in the 12-25 nm wavelength range

To develop polarizer functioning in the extreme ultraviolet (EUV) and soft X-ray region, the polar- ization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equations and optical constants from the Henke database. The reflectance of synthetic mica crystal for s and p polarization was measured to investigate its polarization performance in a home-made synchrotron radiation soft X-ray polarimeter at beamline 3W1B, Beijing Synchrotron Radiation Facility (BSRF). The reflectivity of the synthetic mica crystal at an angle of grazing incidence of 48° was obtained from the experimental data, which is about 4.8x10<'-3> at 25 nm and 6.0×10<'-4> at 12 nm, and the linear polarizance of the X-ray reflected by the synthetic mica crystal that we measured using an analyzer-rotating method increases from 80% to 96.6% in this EUV region, while higher than 98.2% in the simulation. The result indicates that this synthetic mica crystal works as a practical polarizer in this EUV region of 12-25 nm, and also in an extensive wavelength region higher than 25 nm.     

Effective surface modification by stimuli-responsive polymers onto the magnetite nanoparticles by layer-by-layer method

Effective surface modification of poly(N-isopropylacrylamide)-based temperature-responsive polymers onto the magnetite nanoparticles was investigated. To achieve this purpose, layer-by-layer method was applied. This technique is based on sequential chemical reactions between the temperature-responsive polymers with carboxyl groups and other another polymers with amino groups. After the polyion complex formation, carbodiimide chemistry was used to cross-link both the functional polymers. As a result, we could confirm the successful preparation using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and the dispersion measurement of the modified magnetite nanoparticles. The thickness was tunable be the number of the layer-by layer reaction. As expected, the magnetite nanoparticles show the very sensitive temperature-responsive behavior.     

Buckling Behavior of Carbon Nanotubes Functionalized with Carbene under Physical Adsorption of Polymer Chains: a Molecular Dynamics Study

The buckling analysis of functionalized carbon nanotubes (CNTs) is of great importance for the better understanding of mechanical behavior of nanocomposites. The buckling behavior of carbene-functionalized CNTs (cfCNTs) under physical adsorption of polymer chains (cfCNTs/polymers) is studied in this paper by the classical molecular dynamics (MD) simulations. In this regard, to investigate the interactions between non-covalent polymer chains and cfCNTs, two different non-covalent functional groups, i.e. polycarbonate (PC) and polypropylene (PP), are selected. The findings are compared with those of pure CNTs under the physical adsorption of polymer chains (pCNTs/polymers). The obtained results show that at a given weight percentage of non-covalent functional groups, the gyration radius of cfCNTs/polymers is higher than that of pCNTs/polymers. Furthermore, an increase in the critical buckling force of cfCNTs/polymers is dependent on the type of non-covalent polymer chains. For cfCNTs/PC and cfCNTs/PP, the critical buckling force is respectively lower and higher than that of pCNTs/polymers for the similar weight percentage of non-covalent functional groups. In addition, it is found that the critical buckling strain of cfCNTs/polymers is smaller than that of pCNTs/polymers for the same weight percentage of non-covalent polymer chains.     

Plasma-based introduction of monosort functional groups of different type and density onto polymer surfaces. Part 1: Behaviour of polymers exposed to oxygen plasma

Several approaches were investigated to produce monosort functionalized polymer surfaces with a high density and homogeneity of functional groups: (i) Plasma oxidation followed by wet-chemical reduction, (ii) formation of radicals and grafting on of functional group carrying molecules, (iii) plasma bromination followed by (iv) Williamson or Gabriel-like synthesis of spacer molecules, and (v) a pulsed plasma polymerization of functional groups bearing monomers or (vi) their copolymerisation with other comonomers. The formation of hydroxyl (OH), primary amino (NH₂), and carboxyl (COOH) groups was studied in detail. The oxygen plasma treatment (i) in a low-pressure non-isothermal glow discharge results in the formation of a wide variety of O functional groups, polymer degradation and crosslinking. Low power densities and short exposure times (0.1 to 2 s) are required to functionalize a surface while preserving the original polymer structure. Carbonate, ester, and aromatic groups are rapidly degraded by an oxygen plasma treatment leading to scissions of polymer backbones and loss in molecular weight. Also the formation of macrocycles and C=C bonds was observed in a region of around 4 nm in depth. The investigated polymers could be classified by their degradation behaviour on exposure to the oxygen plasma. In order to maximize the process selectivity for OH groups, the variety of oxygen functionalities formed by the oxygen plasma was wet-chemically reduced by diborane, vitride? (Na complex), and LiAlH₄. Typical yields were 9 to 14 OH groups per 100 carbon atoms. Plasma bromination (iii) (40 Br per 100 C atoms) of polymers, followed by grafting of spacer molecules (iv), has been proved to be a highly selective reaction. Another way to produce high densities of monosort functionalities was the pulsed plasma polymerization of functional group bearing monomers such as allylamine, allylalcohol or acrylic acid (v). The retention of chemical structure and functional groups during plasma polymerization was achieved by using low power densities and the pulsed plasma technique. The maximum yields were 30 OH, 18 NH₂, and 24 COOH groups per 100 C atoms. To vary the density of functional groups a chemical copolymerization with 'chain-extending' comonomers such as butadiene and ethylene was initiated in the pulsed plasma (vi). Additionally, the often-observed post-plasma oxidations of such layers initiated by reaction of trapped radicals with oxygen from the air were successfully suppressed by using NO gas as radical quencher.     

Desorption electrospray ionization - orbitrap mass spectrometry of synthetic polymers and copolymers

Desorption ElectroSpray Ionization (DESI) - Orbitrap Mass Spectrometry (MS) was evaluated as a new tool for the characterization of various industrial synthetic polymers (poly(ethylene glycol), poly(propylene glycol), poly(methylmethacrylate), poly(dimethylsiloxane)) and copolymers, with masses ranging from 500 g.mol(-1) up to more than 20?000 g.mol(-1) . Satisfying results in terms of signal stability and sensitivity were obtained from hydrophobic surfaces (HTC Prosolia) with a mixture water/methanol (10/90) as spray solvent in the presence of sodium salt. Taking into account the formation of multiplied charged species by DESI-MS, a strategy based on the use of a deconvolution software followed by the automatic assignment of the ions was described allowing the rapid determination of M(n) , M(w) and PDI values. DESI-Orbitrap MS results were compared to those obtained from matrix-assisted laser desorption/ionization- time-of-flight MS and gel permeation chromatography. An application of DESI-Orbitrap MS for the detection and identification of polymers directly from cosmetics was described. Copyright ? 2012 John Wiley & Sons, Ltd.     

The compression of polymer brushes under shear: the friction coefficient as a function of compression,shear rate and the properties of the solvent

We present a study of the compression of polymer-grafted surfaces using the dissipative particle dynamics (DPD) method at constant chemical potential. We demonstrate the importance of performing simulations of compression at fixed chemical potential of the solvent by comparing the simulated force-compression curves at constant chemical potential and density with the experimental profile determined for poly(ethylene-propylene) chains grafted onto mica surfaces in a cyclohexane solvent. The simulated force-distance and friction profiles are presented as a function of the polymer grafting density, the shear rate and the nature of the solvent. We also study the influence of the steepness of conservative potential between polymer segments and the size of the solvent elements (particles) on the form of the force-compression and friction-compression profiles.     

Combinatorial study of nanoparticle dispersion in surface-grafted macromolecular gradients

Surface-tethered assemblies of polymers with gradually varying molecular weight (MW) and/or grafting density are utilized to control the dispersion of nanosized particles. Using several case studies we show that these gradient polymer specimens represent ideal systems for combinatorial exploration of the parameters that control the distribution of the particles in surface-grafted layers. We demonstrate that the particle distribution is governed by the interplay between the particle size and the grafting density and molecular weight of the polymer brush.     

A facile method for grafting of bisphenol A imprinted polymer shells onto poly(divinylbenzene) microspheres through precipitation polymerization

Core-shell structured polymers are usually prepared by “grafting to” or “grafting from” techniques, wherein polymer supports were first modified by vinyl bonds or initiators. Success can be immediate, but more often a learning curve needs to be traversed. In this paper, direct grafting bisphenol A imprinted polymer onto poly(divinylbenzene) microspheres through precipitation polymerization is introduced. The obtained microspheres were characterized by SEM, TEM, FTIR and BET. Firstly, mono-disperse poly(divinylbenzene) microspheres of 3 μm in size were prepared by precipitation polymerization. The solvent for grafting was then optimized and it was found that the mixtures of toluene and acetonitrile (30/70, v/v) were ideal choice from the image and structure analysis of the shells. Shells of different thickness (270-840 nm), depending on the concentrations of monomers in the precursor, were then directly grafted to the microspheres by a reactive, entropic capture mechanism. The recognition ability of the microspheres was evaluated by solid-phase extraction and clear selectivity showed toward bisphenol A. The leak of bisphenol A was not found after extraction and thus these core-shell structured imprinted polymers are believed to have potential applications in trace analysis area.     

Effect of high pressure on radiation-induced cross-linking of synthetic rubbers

The effect of pressure on the radiation-induced cross-linking of synthetic rubbers, cis-l,4-polybutadiene, cis-l,4-polyisoprene, poly(TFE-propylene), poly(styrene-butadiene), poly(ethylene-propylene), and trans-l,4-polybutadiene were studied. A remarkable acceleration of cross-linking by compression for unsaturated polymers is attributed to an acceleration of the propagation reaction of cross-linking, which does not require long-range migration of radicals, by reduction of the distance between polymer chains at high pressure while the termination reaction, which requires long-range migration of radicals to recombine with each other, is reduced by the decrease in mole-cular mobility at high pressure. The presence of an optimum pressure was observed for radiation-induced cross-linking of cis-l,4-polyisoprene and TFE-propylene copolymer. This is explained by a significant change in molecular motion occurring due to the glass transition or crystallization at high pressure.     

Hydrophilic surface formation on polymers and its applications

A new surface modification technique, so-called ion assisted reaction (IAR) has been developed at the Korea Institute of Science and Technology (KIST) Ion Beam Laboratory while modifying the surface of polymer results in many of industrial applications. The IAR, in which a keV ion beam is irradiated on the surface of polymer in reactive gases environment, has been developed for improving wettability of polymer surface and enhancing adhesion of other materials. The contact angles of water drops with modified polymers were significantly reduced by Ar⁺ ion irradiation with flowing oxygen gas environment than without flowing oxygen gas. Change of contact angles for the modified polymers was explained by a two-step chemical reaction among polymer matrix, energetic ions and oxygen gas. X-ray photoelectron analysis showed that hydrophilic groups were formed on the surface of polymers by chemical reaction between the unstable chains induced by ion irradiation and the oxygen gas, and the hydrophilic groups were identified as –(C–O)–, –(CO)– and –(CO)–O– bonds. The enhanced adhesion between metal and modified polymers was explained by the formation of charge transfer complex in polymer and electron donors in metal. Possible industrial applications of the IAR are to be discussed.     

Single molecule lifetime fluctuations reveal segmental dynamics in polymers

We present a single molecule fluorescence study that allows one to probe the nanoscale segmental dynamics in amorphous polymer matrices. By recording single molecular lifetime trajectories of embedded fluorophores, peculiar excursions towards longer lifetimes are observed. The asymmetric response is shown to reflect variations in the photonic mode density as a result of the local density fluctuations of the surrounding polymer. We determine the number of polymer segments involved in a local segmental rearrangement volume around the probe. A common decrease of the number of segments with temperature is found for both investigated polymers, poly(styrene) and poly(isobutylmethacrylate). Our novel approach will prove powerful for the understanding of the nanoscale rearrangements in functional polymers.     

Detection of the X-ray spectra of imploding neon Z-pinch with elliptically bent mica crystal spectrometer

A wide variety of X-ray and extreme ultraviolet diagnostics are being developed to study on Yang acceler- ator. An elliptically bent crystal spectrometer is designed with a focal length of 1350 mm. A mica crystal with an interplanar spacing of 1.984 nm bent onto an elliptical substrate with eccentricity of 0.9485 is used. The crystal analyzer covers the Bragg angle range from 30° to 60°. The mica crystal can efficiently reflect radiation in multiple orders, covering the entire spectral range from 0.1 to 1.73 nm except for a gap from 0.86 to 1.0 nm. The application experiment is performed on Yang accelerator using the bent mica crystal analyzer. Spectra of neon-puff Z-pinch plasmas are recorded with a X-ray film, showing the H-like and the He-like lines of neon. Each spectrum has been identified and used for the wavelength calibration, and most of the line radiation is contained in the He-α and the L-α lines. The experimental results have demonstrated that the spectral resolution approximates 379.