Empirical polarity parameters for various macromolecular and related materials

Empirical polarity parameters are recommended as useful characteristics for describing the internal and external surface properties of various solid materials, e. g. synthetic polymers, native polymers, inorganic oxides, sol‐gel hybrids, and composites. The polarity properties of a macromolecule have been expressed by three independent terms: the α value (the hydrogen bond donating, HBD, capacity or acidity), the β value (the hydrogen bond accepting, HBA, capacity or basicity), and the π* value (the dipolarity/polarizability). These terms can be defined using the Kamlet‐Taft solvents parameter set as the reference system. A complex property, XYZ, of a macromolecular material under study, with reference to a standard system (XYZ)₀ (i. e. gas phase or a nonpolar polymer), can then be described by a simplified Kamlet‐Taft LSE (linear solvation energy) equation: XYZ = (XYZ)₀ + sπ* + aα + bβ. a, b, and s are coefficients reflecting the susceptibility of the polarity terms upon XYZ. Empirical solvatochromic polarity parameters [α, β, π*, E_T (30)] for synthetic polymers, copolymers, native polymers, inorganic oxidic materials, functionalized silica particles, hybrids, and composite materials have been determined by means of the following solvatochromic probe dyes: 2,6‐diphenyl‐(2,4,6‐triphenyl‐1‐pyridinio)‐4‐phenolate ( 1 a ), Michler's ketone ( 2 ), dicyano‐bis(1,10‐phenanthrolin)iron II ( 3 ), and a novel aminobenzodifuranone dye ( 7 ). The solvatochromic band shifts of these indicators correlate precisely with the Kamlet‐Taft solvent parameters α, β, and π*. The results are compared with each other, with related solvent model compounds, and literature values. The relation of the well established E_T (30) solvent polarity scale to the Kamlet‐Taft parameters α and π* of solid materials is demonstrated. Hence, a general polarity scale for solid materials is suggested.     

Mark-Houwink方程中系数的意义及应用探索——K值的意义及对高分子特性的评估

K值是Mark Houwink经验公式 ([η]=KMα)中的两个常数之一 .理解它的意义不仅有利于公式的应用 ,而且有可能有利于从不同的角度认识高分子材料的性质 .考虑到K是由高分子材料和使用的溶剂性质所决定的 ,因此引入溶剂的一些参数对Mark Houwink经验公式中的K的意义进行了初步探讨 .结果显示 ,高聚物的K和溶剂的极性参数 ,如Reichardt的Et(30 )及Kamlet Taft的π 之间有一定的线性关系 ,而根据这些关系外推发现所有这些被引用的高分子材料似乎可以由此被划分成两大类 ,并进一步推导出高分子材料的极性 .此简易方法得出的数据得到文献和近来的有关研究结论的认可 .     

Determination of polarity parameters for liquid crystals using solvatochromic method in anisotropic and isotropic phases

The use of liquid crystals (LCs) as anisotropic solvents is desired for various potential applications and usually for other organic and inorganic compounds. In this work, solvent polarity parameters are obtained using a spectroscopic method for four LCs with a range of high and low dielectric anisotropy (?ε). Solvatochromic polarity parameters for these LCs were defined via Kamlet–Abboud–Taft polarity functions characterizing different temperatures and phases, isotropic and anisotropic, and using the Reichardt’s dye and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio) phenolate standard probe. The investigated polarity parameters reveal the effects of LC media on the photo-physical behaviour of solute molecules in isotropic and anisotropic media. Subsequently, a new LC polarity parameter (Z_o) is introduced as an overall matrix anisotropy polarity parameter to characterize variation between isotropic and anisotropic phases. The values of Z_o are sorted from higher to lower dielectric anisotropies (?ε).     

Control of adsorption and solubility in gradient high performance liquid chromatography 1. Principles of sudden transition gradients and elution characteristics of copolymers from styrene and methacrylates

Summary Proper retention of polymers in high performance liquid chromatography often requires injection into a starting eluent which is not a solvent for the sample under investigation. In this case, the polymer is precipitated at the top of the column. Subsequent gradient elution has to be performed by addition of an eluent with sufficient chromatographic strength and solvent power. In normal phase chromatography, it must be a solvent of high polarity. With the gradient elutions reported so far, polarity and dissolution power were simultaneously increased.The present paper reports the separate control of solvent strength and chromatographic power by applying gradient programs which include sudden addition of a moderately polar solvent. The amount of the latter does not suffice for elution, which is performed by subsequent, controlled addition of a highly polar nonsolvent. Sudden transition gradients of this kind work with, e.g.,iso-octane as a nonpolar starting eluent, tetrahydrofuran as a solvent of intermediate polarity, and methanol as a strongly polar nonsolvent. They have been applied to copolymers from styrene and ethyl methacrylate, methyl methacrylate, or methoxyethyl methacrylate.     

Permeation of water as a tool for characterizing the effect of solvent, film thickness and water solubility in cellulose acetate membranes

Cellulose acetate membranes have been used in many applications; of particular interest are reverse osmosis systems, and as a neutral matrix for incorporation of different polymers (e.g., conducting polymers), inorganic ions (e.g., lanthanides) and organic (e.g., pharmaceutical) compounds. The properties of the new polymers derived from cellulose acetate or blends depend on those of cellulose acetate. This work presents an attempt to find links between thermodynamic and kinetic properties of cellulose acetate membranes in equilibrium with water. Water diffusion coefficients in cellulose acetate membranes are reported, measured with a simple water permeation technique. The comparison of these values with the percentage of water uptake and polymer thickness leads to interesting conclusions related with different polymer properties.     

Sorption of metal cations by alginate-based biosorbents. On the correct determination of the thermodynamic parameters

The paper is focused on the problem of interpretation of the experimental data related to the thermodynamics of metal ions binding by alginate-based biosorbents. When considering the thermodynamic parameters (i.e., changes in the enthalpy and entropy values; ΔH and ΔS, respectively), one can observe large discrepancies between their values even if the considered systems have very similar features. For instance, the binding of copper, cadmium, and lead can be entropy-driven, enthalpy-driven or both entropy- and enthalpy-driven, depending on the considered report. The aim of this paper is to find the reason for this paradox and to discuss the problem of interpretation of the data being usually the base for estimating ΔH and ΔS values. It appears that both numerous "technical" (e.g., pH, ionic strength) and model-related (e.g., monodentate vs. bidentate binding models) parameters can seriously influence the obtained values of thermodynamic parameters. The significance of these two types of factors is discussed in qualitative and quantitative manners. The proposed methods of distinguishing between the "apparent" and the "real" ΔH and ΔS values can be also related to other types of sorption/adsorption systems.     

Sampling of organic volatiles in the atmosphere at moderate and low pollution levels

Several techniques are available for measuring organic volatiles in the atmosphere. For measurements at low and moderate pollution levels (between several μg m^?3 and a fraction of a μg m^?3), the existing methods can be adopted to a broad range of different compounds. Whole-air sampling in stainless-steel containers with metal bellows valves combined with subsequent gas chromatographic separation after preconcentration in the laboratory is probably the best procedure for low and medium molecular weight trace gases of moderate or low polarity and reasonable chemical stability (e.g., hydrocarbons and halocarbons). For organic compounds of lower volatility, adsorptive sampling on non-polar porous organic polymers (e.g., Tenax) and thermal desorption combined with cryotrapping and gas chromatographic separation of the sampled compounds is widely used. However, there are often substantial problems due to artefact formation or loss reactions. Owing to the generally larger sample volumes, these problems are even more pronounced for sorptive sampling techniques combined with sample recovery by solvent extraction. Unfortunately, the general understanding of the various processes of sample degradation due to chemical reactions of reactive components of the atmosphere with each other or with the sorbent is not yet sufficient to allow reasonable estimates of the extent of such interferences without elaborate test procedures.     

New approach for chiral separation: from polysaccharide-based materials to chirality-responsive polymers

Chiral separation that is closely related to daily life is a meaningful research. Polysaccharide-(e.g., cellulose, amylose derivatives) based chiral packing materials afford powerful chiral stationary phases(CSPs) toward a broad range of racemic compounds. However, considering the explosive growth of specific chiral drugs, the separation efficiencies of these CSPs need further improvement, which calls for new approaches and strategies. Smart polymers can change their physical or chemical properties dynamically and reversibly according to the external stimuli(e.g., thermo-, pH, solvent, ion, light, critical parameters for chromatographic separation) exerted on them, subsequently resulting in tunable changes in the macroscopic properties of materials. In addition to their excellent controllability, the introduction of chiral characteristics into the backbones or side-chains of smart polymers provides a promising route to realize reversibly conformational transition in response to the chiral analytes. This dramatic transition may significantly improve the performance of materials in chiral separation through modulating the enantioselective interactions between materials and analytes. With the help of chirality-responsive polymers, intelligent and switchable CSPs could be developed and applied in column-liquid chromatography. In these systems, the elution order or enantioselectivity of chiral drugs can be precisely modulated, which will help to solve many challenging problems that involve complicated enantiomers. In this paper we introduce some typical examples of smart polymers that serve as the basis for a discussion of emerging developments of CPSs, and then briefly outline the recent CSPs based on natural and certain synthetic polymers.     

Fluorescent probes for detection of amphiphilic polymer hydrophobic microdomains: A comparative study between pyrene and molecular rotors

 Cationic amphiphilic polymers (e.g. polyvinylpyridinium bromides and polyvinylimidazo-lium bromides) adopt a compact coiled form in aqueous solutions. In the case of former polymers, the resulting hydrophobic microdomains are evidenced only by fluorescence spectroscopy if a molecular rotor (DMAC) is used as a fluorescent probe, while the behaviour of the latter can be studied in aqueous solution by using both types of fluorescent probes, i.e., pyrene and the molecular rotor. The purpose of the present investigation deals with a comparative study between the magnitude of the local viscosity and the polarity of the hydrophobic microdomains generated by poly(3-hexadecyl-1-vinylimidazolium bromide) in an aqueous medium using pyrene and DMAC as fluorescent probes. Moreover, the results are compared with the data obtained with micelles of conventional surfactants such as the homopolymer repetitive unit model and CTAB. Received: 3 June 1996 Accepted: 29 September 1996     

Prediction of the glass transition temperature of polymers: A model based on the principle of corresponding states

The application of corresponding state principles to describe the properties of polymers is implicit in many of the fundamental studies of polymeric behavior. The seminal works of Prigogine, Hildebrand, Eyring, Flory, Gibbs, and DiMarzio in which multidimensional lattice representations and refined statistical mechanical approaches have been used are the basis for much of today's understanding of the thermodynamic behavior of polymers and their solutions. In this work the lattice energy of a polymer is defined in terms of reduced molecular parameters, and it is assumed that all polymers with the same functional form for their lattice energies will be in corresponding states. A reduced second order transition temperature is defined relative to a characteristic temperature T* = s?*/2kv* c, where the molecular parameters refer to the properties of the repeating segments of the polymer chain. Equations are derived that express the effects of molecular weight, plasticization, degree of crosslinking, and copolymerization on the second order (i.e., glass) transition temperature. In their limits, the equations are shown to reduce in form to equations derivable from free volume theory. They are also used to analyze successfully a variety of glass transition temperature data available in the literature on homogeneous uncrosslinked and crosslinked polymers, plasticized polymers, and random copolymers.     

计算饱和醇异构体标准生成焓的新方法

基于极性叠加原理,在成功设计烷烃异构体和多氯代烷烃生成焓计算新方法的基础上,设计了一种计算多元醇异构体生成焓的新方法,并合理地假定任一异构体的原子化焓等于三种键(C-C、C-H和C-O-H键)的键能、极性叠加能项以及氢键能项的加和.用这一模型拟合24种原子化焓数据,得到了标准生成焓的估算公式.为了检验预测的精确性,又设计了一种预测方法,使用在排除被预测的化合物条件下回归得到的参数,预测该化合物的生成焓.按这种方法,预测了24种异构体的生成焓.通过该5参数预测的相对于实验值的各种误差(平均绝对误差、均方根误差和最大绝对误差)不仅比7参数的基团法预测的对应误差小得多,而且比相应实验数据的误差还要小.与键加和法比较,该方法的模型包含了极性叠加能和氢键能量,该两项代表了主要的非键相互作用能,表征了不同异构体的结构差异,并大大减少了参数.     

Modified Diatomaceous earth as a principal stationary phase component in TLC

Modified natural diatomaceous earth (DE) is a principal component of the stationary phase in normal thin-layer chromatography (TLC) applications and is mixed with commercial silica gel 60GF254 (Si-60GF254). Modification is carried out by flux calcination and refluxing with acid. Natural DE, modified DEs [flux calcinated (FC)DE and FCDE-I), and Si-60GF254 are characterized by scanning electron microscopy and Fourier-transform-IR spectroscopy. Particle size, specific surface area, pore distribution, pore volume, and surface hydroxyl group density parameters of materials are determined by various techniques. FCDE-I and Si-60GF254 are investigated for their usefulness in the stationary phase of TLC both individually and in composition. Commercially available red and blue ink samples are run on layers of Si-60GF254 and FCDE-I individually, and on various FCDE-I and Si-60GF254 mixtures. Butanol-ethanol-2M ammonia (3:1:1, v/v) and butanol-acetic acid-water (12:3:5, v/v) mixtures are used as mobile phases. The polarities of stationary phases decrease, and the retention factor (Rf) values of ink components increase when the FCDE-I content of the stationary phase increases. The properties of the stationary phase can be optimized by adding FCDE-I to Si-60GF254. This study may be useful in understanding both the systematic effects of stationary phase properties [e.g., specific surface area and surface hydroxyl group density, aOH(s)] and those of the mobile phase (e.g., polarity and acidity) on Rf values and the separability of components.     

Biodeterioration of polymers and polymer composite materials

The problem of the biodeterioration of polymers and polymer composite materials is considered. Products made from both thermoplastic and thermosetting polymers are found to undergo biodeterioration. An analysis of methods for investigating biocorrosion is performed. It is established that the application of conventional testing methods under laboratory conditions is restricted due to their complexity and work content, as well as because of the low efficiency at the stage of material development. In connection with this, the possibility of applying indirect investigation methods for the qualitative and quantitative evaluation of biodeteriorations of polymers is considered, and testing is carried out on samples of crosslinked polymers in aerotanks. It is shown that biocorrosion is not caused by the microorganisms themselves, but rather by their waste products, e.g., organic acids and ferments. The possibility of evaluating biocorrosion via modeling biodeterioration using solutions of individual substances (various organic acids) is revealed. Urgent problems of investigations on this topic are defined.     

Infrared Chemical Sensor for Detection of Chlorinated Phenols in Aqueous Solutions Based on a ATR Waveguide Coated with Structural Designed Polymers

A combination of solid phase micro‐extraction (SPME) with attenuated total reflection (ATR) infrared spectrometry provides a fast and sensitive way to detect organic compounds in aqueous solutions. It is especially useful for detection of chlorinated organic compounds in environmental samples. Currently, analyses of organic compounds in aqueous solutions are limited to low‐polarity compounds by the SPME/ATR‐IR sensing method. This limitation was mainly caused by the low polarity nature of the SPME phase. To increase the capability of this method to detect more polar compounds and also to increase the sensitivity in detection of organic compounds, the principle of “like‐dissolve‐like” was used to design a specific SPME phase for a certain class of chlorinated compounds. To demonstrate this concept, chlorinated phenols were used as probe molecules and polyvinyl chloride was chemically modified with phenol, ‐naphthol and ‐naphthol to provide SPME phases with a similar chemical structure to chlorinated phenols. These polymers were used as SPME phases and their performance were compared with the commonly used SPME phases (i.e., polystyrene and polyisobutylene). Results indicated that naphthols attached to PVCs provided much lower compactness, which allows fast speed in absorption of phenols. Meanwhile, due to the structural similarity between naphthols attached to PVCs and phenols, much higher partition coefficients were found for these chemically modified PVCs than conventionally used polymers. To further increase the sensitivity for analysis of chlorinated phenols, the common influencing factors, such as pH values and salt effect were also investigated. Apparently, pH values of the solutions did not influence the structure of the modified PVCs significantly. In absorption of chlorinated phenols in aqueous solutions with different pH values, the observed IR signals were decreased greatly in pH higher than 6 due to the charged form of chlorinated phenols that were presented. Results of the salt effect indicated that three times stronger of IR signals can be obtained if 20% (w/vol) of NaCl was added.     

Methods for the determination of binding constants by capillary electrophoresis

Apparent equilibrium constants for molecular association (e.g., association constants, binding constants, dissociation constants, partition coefficients) can be determined with a variety of different capillary electrophoresis (CE) approaches. In many cases, the investigated association behavior is between a smaller molecule or ion (i.e., the solute, drug, or analyte of interest) and a larger entity (e.g., proteins, micelles, polymers, chiral selectors such as cyclodextrins, etc.). Each experimental approach has advantages and disadvantages. Frequently, it is the nature of the system being evaluated that determines the optimal experimental approach. Six different CE-based techniques for evaluating binding constants are reviewed. Examples of each method, and recent references on its use are given.     

Photo-attaching functional polymers to cellulose fibers for the design of chemically modified paper

We introduce a novel approach for preparing polymer-modified and chemically microstructured paper substrates by a photo-chemical attachment of functional polymers to cellulose microfibers inside model filter papers. Poly(methyl methacrylate), PMMA copolymers, which carry a defined amount of photo-reactive benzophenone functional groups, are adsorbed to paper substrates from solution by a simple dip coating process, followed by covalent attachment of the physisorbed polymers through UV-light irradiation. Non-bound macromolecules can be removed from paper sheets by simple solvent extraction, and the resulting polymer-modified substrates were analysed with respect to chemical identity, attached polymer mass, and homogeneity of the polymer attachment. The amount of paper-attached polymers can be conveniently controlled in a wide range from a few mg/g cellulose fiber up to several tenth of mg/g cellulose fiber, by adjusting the polymer concentration in the coating solution. Polymers are being attached by photo-chemical means, and chemical micro patterns on paper can be designed by lithographical means. In first proof-of-concept studies, millimeter-scale channels were prepared that can be used to control fluid penetration by capillary actions. Because of the modularity in the design of photo-reactive polymers, a number of different chemically microstructured papers can be envisioned which may become potentially interesting in lab-on-paper devices.     

Diverse Role of Solvents in Controlling Supramolecular Chirality

Supramolecular self-assembly stands for the spontaneous aggregation of small organic compounds or polymers into ordered structures at any scale. When being induced by inherent molecular chiral centers or ambient asymmetric factors, asymmetric spatial arrangement between building units shall occur, which is defined as supramolecular chirality. Except for molecular design, utilizing external stimulus factors to tune supramolecular chirality is a promising approach. In this Concept article, we particularly discuss the important role of solvents in manipulating the chirality of self-assembled systems. The impact of solvents on the chirality is generally based on three properties of solvents, i.e., chirality, polarity, and active coassembly with building blocks. Molecular self-assembly in chiral solvents could undergo the chirality transfer, exhibiting a chiral induction effect. Solvent polarity often determines intermolecular orientation. As a consequence, those building blocks with both polar and apolar segments might change their chirality depending on the solvent polarity. We elaborate the active participation of solvent molecules into ordered structures together with building blocks, where solvents and building blocks exhibit a coassembly manner. By specific treatments such as heating and cooling, solvents could be released or re-entrapped, allowing a smart control over supramolecular chirality. The solvent effect in manipulating two-dimensional chiral self-assemblies is then discussed. The perspective and future development in this research field are presented at last.     

Ion-pair extraction of some sympathomimetics: Description of an extraction model for terbutaline and investigation of some factors influencing the recovery of sympathomimetics

The ion-pair formation of terbutaline, a resorcinolamine, was studied during extraction into ethyl acetate, a slightly polar organic solvent. Factors influencing the extraction, e.g., the concentration of various ions in the aqueous phase, are considered. Terbutaline is extracted as a simple ion-pair without the formation of higher adducts. The extraction of some Sympathomimetics is also described with respect to the nature of the organic solvent, the drug and the extracting anion. Factor analysis is applied to the data, and the reliability of predicted values is discussed. A search for a correlation between the factor analysis parameters characterizing the aqueous—organic phase systems and their physical properties led to a correlation between these parameters and interfacial tension; this result is explained by the macroscopic model of a solid surface (i.e., of the extracted compound) in contact with two fluids.     

Characterization of Convection for Molecularly Imprinted Monolith

Convection of molecularly imprinted polymers monolith in LC mode was discussed in this paper. On the MIPs monolith reported here, a flat van Deemter plot of height equivalent to a theoretical plate (HETP) versus superficial velocity was observed. This typical behavior, similar to perfusion packings, suggests that the unique pore structure of the MIPs monolith allowed convection-enhanced mass transfer. Column parameters, e.g., external porosities, internal porosity, column permeability and equivalent sphere dimension, were obtained. Intraparticle Peclet number (λ) was used to characterize the convection in the monolith. In addition, a ratio of the numbers of transfer units, T, for diffusion in the micropores and through-pores has been introduced to quantify the relative importance of the contribution from convection and diffusion to mass transfer. The results show that the flow in a MIP monolith is extremely sensitive to pore size distribution and can be tuned by polymerization parameters.