Synthesis and light gas separations in cross-linked gemini room temperature ionic liquid polymer membranes

Cross-linkable gemini room temperature ionic liquids (GRTILs) were synthesized and photo-cross-linked into thin films. The resultant polymer membranes were tested for their permeabilities to CO₂, N₂, CH₄ and H₂. Permeabilities for each gas were found to be much lower when compared to previously reported poly(RTIL) membranes, mainly as a result of highly restricted diffusion. Separation factors were similar to previously studied poly(RTIL) membranes. CH₄ and N₂ fluxes were small enough to consider these membranes as “barrier” films to the transport of those gases. Poly(GRTILs) may have use in applications where flow of those gases is not desirable.     

Analytical applications of second-order calibration methods

Second-order calibration methods are gaining widespread acceptance among the analytical community mainly because: (1) a wide range of analytical instrumentation is available that enables high dimensionality data to be obtained; (2) the chemometric techniques for treating these data are highly developed; and (3) they have the so-called “second-order advantage”, i.e. they can predict the concentration of the analyte of interest even in the presence of unknown interferents. This also enables several analytes to be determined simultaneously.In this paper we describe the most common instrumental and chemometric techniques used in second-order calibration and discuss their applications since 2000. First, we introduce briefly the techniques and then we comment the applications. Given the practical nature of this paper, we have classified the techniques according to five fields of application: pharmaceuticals, biological matrices, foods, environmental matrices and synthetic matrices.     

Modeling the solid-like behavior of entangled polymer nanocomposites at low frequency regimes

A theory for the linear viscoelastic behavior of entangled polymeric liquids reinforced with non-aggregated colloidal nanoparticles is presented. Composites with low filler concentration and strong polymer-particle interaction are considered. A fraction of entangled chains is assumed to be reversibly adsorbed on the surface of fillers, due to the affinity between the polymer molecules in the matrix and dispersed filler particles. The relaxation of the system is analyzed by the combination of stress relaxation functions for free and adsorbed polymer chains. It is demonstrated that the emergence of solid-like behavior at low frequency regimes, is due to the significant slow down in relaxation of adsorbed chains. Fitting the model predictions with relevant experimental data indicates that while the effect of constraint release should be considered to obtain a reasonable estimation of neat polymer behavior, the linear combination of stress relaxation functions of free and adsorbed chains (i.e., no thermal constraint release) leads to a better agreement with experimental data of filled systems.     

Rheological properties of asphalt/SBS/clay blends

The effect of the addition of clay as a third component in polymer modified asphalts has been investigated. After a preliminary investigation on the binary asphalt/clay and polymer/clay blends, the tertiary blends were prepared by adding the clay and polymer to the asphalt, either separately or in the form of a premixed master batch. Intercalated nanocomposites with comparable interlayer distances and glass transition temperatures were obtained in both cases. However, the results show that the mixing procedure significantly affected the final rheological properties. The master curves built in the linear viscoelastic range and represented in both the frequency and the temperature domains help to visualize and evaluate such differences.     

Characterization of PVdF-HFP/Nafion/AlO[OH]n composite membranes for direct methanol fuel cell (DMFC)

Poly-(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP)/Nafion ionomer/aluminum oxy hydroxide nanocomposite membranes were prepared by phase inversion technique. The resultant membranes were subjected to protonic conductivity, methanol permeability, infra-red and thermogravimmetric analysis. The infra-red spectroscopic measurements revealed the presence of sulfonic acid groups in the composite membranes. The thermal stability and ionic conductivity of the polymer membranes have been greatly varied upon the addition of AlO[OH]_n. Although the PVDF-HFP/Nafion/AlO[OH]_n composite membranes have moderate protonic conductivity it has lower methanol permeability and may be considered as a candidate for DMFC applications.     

Evidences of macromolecular chains confinement of ethylene–propylene copolymer in organophilic montmorillonite nanocomposites

A random ethylene–propylene copolymer (EPM) functionalized with grafted diethylsuccinate groups was melt blended with increasing amount (to 20 wt%) of organophilic montmorillonite (OMMT) to prepare nanocomposites with different morphologies as evidenced by XRD and TEM analysis. All the nanocomposites were treated with boiling toluene that did not extract a significant amount of EPM. The increase of not-extracted EPM with the increasing quantity of OMMT suggested strong interactions of the polymer chains with the inorganic substrate. The DSC measurements of nanocomposites and the corresponding insoluble residues revealed a higher T_g values with larger amount of inorganic particles. The dielectric relaxation analysis confirmed the evidence of strong interactions among montmorillonite and the polar diethylsuccinate groups for the macromolecules trapped due to the presence of the inorganic layers. The results were discussed with reference to their relevance as an evidence of nanoconfinement at polymer clay interface and correlated with the clay basal distance variation due to the intercalation process.     

Preparation and proton conductivity of acid-doped 5-aminotetrazole functional poly(glycidyl methacrylate)

Proton conducting polymer membranes have become crucial due their applications in fuel cells as source of clean energy. In this work, we synthesized poly(glycidyl methacrylate) (PGMA) by conventional free radical polymerization of GMA using azobisisobutyronitrile (AIBN) as initiator. PGMA was modified with 5-aminotetrazole by ring opening of the epoxide group. The composition of the polymer was studied by elemental analysis (EA) and the structures were characterized by FT-IR and solid ¹³C NMR spectra. Thermogravimetry analysis (TG) and differential scanning calorimetry (DSC) were employed to examine the thermal stability and homogeneity of the materials, respectively. Polymers were doped with H₃PO₄ at several stoichometric ratios. The effect of doping on the proton conductivity was studied via impedance spectroscopy. Maximum proton conductivity of acid-doped PGMA-aminotetrazole was found to be 0.01 S/cm at 150 °C in the anhydrous state.     

Synthesis of polypeptide/inorganic hybrid block copolymers

Polypeptide/inorganic hybrid copolymers were obtained by a four-step synthetic approach combining (i) atom transfer polymerization of tert-butyl acrylate, (ii) chemical modification of the bromo end groups of ATRP-polymers into primary amino group using Gabriel reaction, (iii) ring opening polymerization of N_ε-trifluoroacetyl-l-lysine or γ-benzyl-l-glutamate N-carboxyanhydrides followed by (iv) the transamidification reaction using a large excess of (3-aminopropyl)trimethoxysilane to substitute the tert-butyl groups of the poly(tert-butyl acrylate) block. Products were characterized using ¹H NMR, FT-IR, DSC and MALDI-TOF MS. These techniques proved that polymerization of tert-butyl acrylate was controlled whatever the molecular weight targeted and that bromide was quantitatively converted to amino end group by a original method leading to the synthesis of copolymers in the presence of N-carboxyanhydrides as monomers. Amphiphilic polypeptide/inorganic hybrid copolymers were then achieved.     

High density polyethylene-grafted-maleic anhydride low-k porous films prepared via thermally induced phase separation

Low dielectric constant (low-k) porous films of high density polyethylene-grafted-maleic anhydride were prepared via thermally induced phase separation (TIPS) using di-n-octyl phthalate as the solvent and methanol as the extractant. The results show that, for the process of TIPS, cellular structures of spherical pores were obtained. Lower polymer concentration and lower cooling rate induced larger pores and higher porosity. For the dielectric constant, the introduction of pores considerably reduced the dielectric constant from 2.60 to 1.56 at most. Pore size showed little effect on dielectric constant in our experiment, but porosity was found to be the key influential factor. The relationship between dielectric constant and porosity was found to be best fit to Rayleigh model.     

双峰聚合物分子刷的层化机理

建立了用于模拟双峰聚合物分子刷相结构的自洽场理论. 模拟结果表明, 良溶剂条件能够促使双峰聚合物分子刷裂分为内外两个亚分子层, 其中短链居于内分子层, 而长链伸展到外分子层. 体系溶解性的加强不仅使聚合物的密度分布逐渐趋近强分凝理论的解析结果, 而且加大了分子链的伸展和链段的局部取向程度. 分子链接枝密度的增加能够促使分子刷的层化, 并且在良溶剂区域, 不同接枝密度的分子链密度分布可以回归到同一条主线. 在良溶剂条件下, 长链的聚合度对短链的密度分布影响不大, 但能够导致长链向外分子层扩展.