Effect of polymer loading on the electrical and thermodynamic properties in relation to gas chromatographic applications

Different layers, 5, 10, 15, and 25% (w/W), of the three studied polyethylene glycols (PEGs) having different molecular weights, 600, 4000, and 20,000, were used for coating on chromosorb pink acid washed (P AW). The polarity and selectivity of the prepared packing columns and their thermodynamic parameters were determined via inverse gas chromatography. The effect of polymer‐layer thickness on the polarity was studied dielectrically. The dependence of specific retention volume, enthalpy, and entropy upon the loading of polymer on support were also studied. In all investigated polymers, the loads 5 and 10% deactivate the support surface, resulting in a decrease in its capacitances, which reflects the polarity. The loads 15% PEG20,000 and 25% PEG4000 can elute n‐alcohols and exhibit high efficiency of separation; however, in the case of PEG600, loading has to exceed 25% to be sufficient for eluting n‐alcohols. The lower thickness of the coated polymers was preferred for good separation of saturated hydrocarbons and also for cyclohexane and aromatic hydrocarbons. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1709–1717, 2001     

Determination of mean molecular weight of polyethylene glycols by several physical methods

Several physical methods were used for the determination of the mean molecular weight of polyethylene glycols (PEG). Gas chromatography proved to be the best method to obtain a molecular weight of PEG lower than 600 by using Tenax as a stationary phase. Reverse gas chromatography was long but valid for PEG between 400 and 3000. Viscosity measurements gave more suitable values by taking different Mark–Houwink constants according to the molecular weight of PEG. Gel permeation chromatography using the universal calibration method was shown reliable, and by means of three μ-Styragel phases (100, 500, and 10⁴ Å) the molecular weight range between 200 and 20,000 was covered. Infrared measurements were related to the molecular weight by taking the OH absorbing band, and a result for PEG of 5000 or less was obtained. Vapor pressure measurements as made in tonometry were an accurate and sensitive method.     

Modification of ABS Membrane by PEG for Capturing Carbon Dioxide from CO2/N2 Streams

Carbon dioxide capture and storage (CCS) has been propounded as an important issue in greenhouse gas emissions control. In this connection, in the present article, the advantages of using polymeric membrane for separation of carbon dioxide from CO₂/N₂ streams have been discussed. A novel composition for fabrication of a blend membrane prepared from acrylonitrile-butadiene-styrene (ABS) terpolymer and polyethylene glycol (PEG) has been suggested. The influence of PEG molecular weight (in the range of 400 to 20000) on membrane characteristics and gas separation performance, the effect of PEG content (0–30 wt%) on gas transport properties, and the effect of feed side pressure (ranging from 1 to 8 bar) on CO₂ permeability have been studied. The results show that CO₂ permeability increases from 5.22 Barrer for neat ABS to 9.76 Barrer for ABS/PEG20000 (10 wt%) while the corresponding CO₂/N₂ selectivity increases from 25.97 to 44.36. Furthermore, it is concluded that this novel membrane composition has the potential to be considered as a commercial membrane.     

椰油丙基酰胺甜菜碱/聚乙二醇水溶液的分相研究

Phase separation behavior of cocamidopropyl betaine/water/polyethylene glycol (PEG) system was studied. The effects of concentration and molecular weight of PEG on the phase separation behavior were investigated. Clouding occurred when the con-centration of PEG was large enough in the betaine aqueous solution, and the concentration of PEG at cloud point decreased with the increase of PEG molecular weight for a constant betaine concentration. The bottom phase was the PEG-rich phase, and the upper phase was the betaine-rich phase. The volumetric ratio of PEG-rich phase to betaine-rich phase, at the same difference between the PEG concentration and the one at the cloud point, Ccp (0.1 g•ml－1), decreased as the PEG molecular weight increased and approached 1 for higher PEG molecular weight (about 20000), which was similar to the typical aqueous two-phase system. This volumetric ratio depended on the initial PEG concentration, but independent of PEG molecular weight. The concentration ratio of betaine to PEG in both phases depended on the Ccp, independent of PEG molecular weight.     

Synthesis of PEG‐functionalized poly(diphenylacetylene)s and their gas permeation properties

The polymerizations of 1‐(3‐methylphenyl)‐2‐(4‐trimethylsilyl)phenylacetylene ( 1a ) and 1‐(4‐methylphenyl)‐2‐(4‐trimethylsilyl)phenylacetylene ( 1b ) were carried out with TaCl₅‐n‐Bu₄Sn to give relatively high‐molecular‐weight polymers ( 2a and 2b ) (M_n > 5 × 10⁵). The obtained polymers were brominated by using benzoyl peroxide and N‐bromosuccinimide first, followed by substitution reaction of three types of polyethylene glycol. When diethylene glycol was used as a reagent on substitution reaction of meta‐substituted polymer, PEG‐functionalized poly(diphenylacetylene) with the highest content of oxyethylene unit [ 4a(2) ] was obtained, and the degree of substitution was 0.60. The degrees of substitution decreased to 0.15 and 0.08 when the polyethylene glycols with higher molecular weights were used. PEG‐substitution reaction to the para‐substituted polymers was difficult to proceed, and hence the degree of substitution was 0.18 even when diethylene glycol was used. The CO₂/N₂ separation factor of PEG‐functionalized polymer [ 4a(2) ] was as large as 28.8, although that of 2a was 7.41. The other PEG‐functionalized polymers also exhibited high CO₂ permselectivity, and their CO₂/N₂ separation factors were over 20. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Formation of microcapsules of medicines by the rapid expansion of a supercritical solution with a nonsolvent

The rapid expansion from a supercritical solution with a nonsolvent (RESS‐N) was applied to the formation of polymeric microcapsules containing medicines such as p‐acetamidophenol, acetylsalicylic acid, 1,3‐dimethylxanthine, flavone, and 3‐hydroxyflavone. A suspension of medicine in carbon dioxide (CO₂) containing a cosolvent and dissolved polymer was sprayed through a nozzle to atmospheric pressure. The pre‐expansion pressure was 10–25 MPa, and the temperature was 308–333 K. The polymers were poly(L ‐lactic acid) (molecular weight = 5000), poly(ethylene glycol) (PEG; PEG4000, molecular weight = 3000; PEG6000, molecular weight = 7500; and PEG20000, molecular weight = 20,000), poly(methyl methacrylate) (molecular weight = 15,000), ethyl cellulose (molecular weight = 5000), and PEG–poly(propylene glycol)–PEG triblock copolymer (molecular weight = 13,000). The solubilities of the polymers as coating materials and these medicines as core substance were very low in CO₂. However, the solubilities of these polymers in CO₂ significantly increased with the addition of low molecular weight alcohols as cosolvents. After RESS‐N, polymeric microcapsules were formed according to the precipitation of the polymer caused by a decrease in the solvent power of CO₂. This method offered three advantages: (1) enough of the coating polymers, which were insoluble in pure CO₂, dissolved; (2) the microparticles of the medicine were encapsulated without adhesion between the particles because a nonsolvent was used as a cosolvent and the cosolvent remaining in the mixture was removed by the gasification of CO₂; and (3) the polymer‐coating thickness was controlled with changes in the feed composition of the polymer for drug delivery. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 742–752, 2003     

Fractionation of low molecular weight polyethylene by high-pressure soxhlet extraction

The use of quantitative, high-pressure Soxhlet extraction for the fractionation of low molecular weight polyethylene samples is described. Liquid carbon dioxide was found to be a suitable solvent for the lowest molecular weight hydrocarbons but failed to solubilize hydrocarbons with molecular weights greater than C-40—C-50. Liquid pentane was found to be an effective solvent for hydrocarbons that were insoluble in liquid CO₂. Careful, stepwise adjustment of the extraction solvent temperature produced polymer fractions with molecular weight distributions substantially narrower than those of the parent materials. Polymer fractions with molecular weights up to C-90 were analyzed by high-temperature gas chromatography. These analyses demonstrated the effectiveness of the technique in fractionating polymers according to molecular weight. Further evidence was provided by thermal analysis of the fractions that indicated melting-point transitions that were much sharper than those of the parent materials. High-pressure Soxhlet extraction offers considerable potential as a general method for purification and fractionation of synthetic and natural polymers. © 1993 John Wiley & Sons, Inc.     

Possibilities of Colloidal Silica Separation from Water Suspension in the Polyethylene Glycol (PEG) Presence at Different Temperatures

The influence of polyethylene glycol (PEG) adsorption on the silica (SiO₂) suspension stability was examined in the range 15–35°C. For this purpose the following methods were applied: turbidimetry, spectrophotometry, and microelectrophoresis. They allow determination of silica suspension stability, its absorbance, and zeta potential of the solid particles in the absence and presence of the polymer. The obtained results indicate that both polymer adsorption and temperature influence the stabilization-flocculation properties of the systems under examination. The silica suspensions without the polymer are relatively stable in the whole range of the investigated temperatures (electroststic stabilization). The adsorption of polyethylene glycol with lower molecular weight (PEG 2000) practically does not change the stability properties of the suspension (steric stabilization), whereas the adsorption of PEG with the higher molecular weight (20000) causes its deterioration (bridging flocculation). The higher the temperature is the greater the effect of destabilization is obtained. Such behavior of the investigated system is the result of changes in the structure of the polymer adsorption layer with the increasing temperature.     

Partition of α-lactoalbumin and β-lactoglobulin from goat milk whey utilizing aqueous biphasic systems

This paper presents a study of α-lactoalbumin and β-lactoglobulin proteins partition from goat milk whey in-nature, utilizing aqueous biphasic systems comprised of polymers (polyethylene glycol, polypropylene glycol, polyvinylpyrrolidone), potassium phosphate, and water. The systems were evaluated at 25°C and pH 7.0. The influence of the polymer type, of the polymer molecular weight, and the polymer mass percentage on the partition coefficient of these proteins was assessed. Among the analyzed polymers, the polyethylene glycol (1500) was more indicated. The results showed that the separation technique by aqueous biphasic systems are applicable indicating high efficiency in the whey proteins separation process.     

Influence of polyethylene glycol molecular weight on the anticancer drug delivery of pH-sensitive polymeric micelle

Polyethylene glycol (PEG) and pH-sensitive polymers have been widely utilized in anticancer drug delivery systems due to their characteristics of prolonging circulation time and tumor-responsive drug release. However, the effect of PEG molecular weight on the delivery of anticancer drug-encapsulating pH-sensitive polymer micelles has been poorly studied. Therefore, a simple method was used to prepare pH-sensitive doxorubicin (DOX)-loaded micelles (DOX/POD) based on polyethylene glycol-2-(octadecyloxy)-1, 3-dioxan-5-amine (POD) polymers, and the influence of PEG molecular weights (1 K, 2 K, and 5 K) on in vitro drug release and antitumor effect was further studied. Interestingly, as the molecular weight increased, the release amount of DOX was augmented. While the cytotoxicity and cellular uptake were increased, the molecular weight was decreased. It is reasonable to speculate that the high molecular weight of PEG may promote the dissolution rate of DOX, and their micelles with uncompact structure are being prone to disassembly in an acid environment. However, the low molecular weight of PEG may contribute to the formation of compact POD micelles, which make it easier to be uptaken by tumor cells resulting in the enhanced antitumor effect. Taken together, the results indicate that pH-sensitive POD micelles with low molecular weight can achieve the efficient delivery of drugs, and PEG molecular weight in pH-sensitive nanocarriers may influence the antitumor effect. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47854.     

A Model for the Prediction of Precipitation Curves for Globular Proteins with Nonionic Polymers as the Precipitating Agent

Abstract

A statistical thermodynamic model for the prediction of precipitation curves of globular proteins using nonionic polymers has been proposed. The model accounts for protein-polymer, polymer-solvent, electrostatic, and hydrophobic interactions as well as the entropy of mixing and employs simplifying assumptions such as spherical globular protein molecule with uniform surface properties and linear, homogeneous polymer uniform with respect to molecular weight. The proposed model can only be employed to predict precipitation curves of charged proteins at sufficiently high ionic strengths since it does not account for electrostatic protein-protein interactions due to overlap of electrical double layers. The model predictions of precipitation curves of human serum albumin (HSA) at the isoelectric point using polyethylene glycol (PEG) for different initial protein concentrations and molecular weights of PEG agreed well with the experimental data. Higher polymer concentrations were found to be required to precipitate proteins for lower molecular weight polymers, lower initial protein concentrations, and more favorable protein-polymer interactions. The HSA-PEG interaction parameter, obtained by fitting the model to experimental data for one molecular weight PEG, was found to be 0.122. Solubility of HSA in PEG solution was found to decrease with increasing salt concentrations, this effect being more pronounced at lower PEG concentrations. The net charge on HSA was found to result in a maximum in its solubility at intermediate salt concentrations as a result of competing salting-in and salting-out effects.     

Separation selectivity of aqueous polyethylene glycol-based separation systems: DSC, LC and aqueous two-phase extraction studies

The distribution behavior of n-alcohols, ketones and nitroalkanes in aqueous liquid chromatography with a column packed with polyethylene glycol (PEG) gel, TSKgel Ether-250, was compared with that in aqueous two-phase systems (ATPSs) formed from PEG and Na₂SO₄ or (NH₄)₂SO₄. The plots of the distribution data obtained for the PEG gel system against those for the ATPS reveal that the separation selectivities exerted by the PEG gel system and the PEG-based ATPS are approximately the same. Differential scanning calorimetry studies on aqueous PEG solutions suggest that PEG polymer forms a hydration structure of which the composition is 50% (w/w) PEG or the hydration number per ethylene oxide is 2.4 and the separation selectivity of the PEG-water systems can be attributed to partition of solute compounds into the hydrated PEG polymer structure.     

A Comparison of Dicoronylene and Octadecylsilica Stationary Phases for Separation of Polycyclic Aromatic Hydrocarbons by Microcolumn Liquid Chromatography

The chromatographic performance of dicoronylene as a stationary phase in microcolumn liquid chromatography has been investigated. The performance has been compared to commercially available polymeric and monomeric octadecylsilica stationary phases. Similarities between polymeric octadecylsilica phases and dicoronylene are found in their planarity recognition capability for polycyclic aromatic hydrocarbons. This is explained by the planar structure of dicoronylene being able to recognize planar solutes in the liquid chromatographic environment, as explained by the “slot model” as proposed by Wise et al.     

Synthesis and characterization of comb‐like polymer PVC–poly(ethylene oxide)

A new series of amphiphilic graft‐copolymers, composed of poly(vinyl chloride) (PVC) backbones and poly(ethylene oxide) side chains, was synthesized by chemical modification of PVC. The synthesis was based on the reaction between chlorine in PVC (polymerization degree 700) and sodium salt of polyethylene glycol (PEG). PEGs with molecular weights of 200 and 600 were used. The graft polymers were characterized by IR and gel permeation chromatography and the molecular parameters such as the average numbers of grafting chains on the PVC backbones were calculated as well as the grafting percent. The molecular weights of PEG were found to influence the rate of the grafting reaction and the final degree of conversion. The maximum grafting percentage of the resulted polymers after the purification was ca. 34%, regardless of the molecular weight of PEG. No gel was observed in the PVC‐g‐PEOs, in spite of the average numbers of grafting chains up to 32. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 475–479, 2000     

High-Pressure Gas Chromatography and Chromatography with Supercritical Fluids. III. Fluid-Liquid Chromatography

Abstract

High-boiling substances can be separated by partition chromatography, using n-pentane and isopropanol under supercritical conditions as mobile carriers. At moderate temperatures (200–250°C) the volatility of heavy substances may be enhanced by a factor of as much as 10⁴ by increasing the pressure from atmospheric to about 50 kg/cm². This enables the analysis of compounds which are too heavy for ordinary gas chromatography.

As predicted before on the basis of gas-chromatographic studies at elevated pressures, the use of supercritical mobile fluids in combination with liquid stationary phases results in an attractive separation procedure. This technique is rapid and has a high degree of flexibility. Separations according to boiling point as well as molecular type are possible.

The main features of the new chromatographic technique, for which the designation “fluid-liquid chromatography” (FLC) is proposed, are illustrated by means of several examples.     

Separation of Bromelain by Aqueous Two Phase Flotation

Aqueous two phase flotation (ATPF) system of polyethylene glycol (PEG) and potassium phosphate is studied for the separation and partial purification of bromelain from the pineapple fruit (Annanus comosus L. Merryl). The effect of PEG molecular weight (1500–20000), concentration of phase forming components (PEG 12–18% w/w and potassium phosphate 14–20% w/w), system pH, nitrogen flow rate, and flotation time were studied and optimum conditions for ATPF were obtained. At optimum conditions of the system, i.e., 14% w/w PEG 1500, 18% w/w potassium phosphate, 80 mL/min of nitrogen flow rate and pH 7, maximum yield of 91.47% and purification fold of 4.26 were obtained. ATPF was found to be an effective technique for the purification of bromelain from pineapple fruit with higher extraction yield and purification fold as compared to aqueous two phase extraction (ATPE).     

气相色谱固定相的演变

简要综述了半个世纪以来气相色谱固定相的发展,在气相色谱发展的初期主要是低分子化合物和工业用高聚物,主要用于填充柱气相色谱,有上千种固定液。到上世纪80年代以后毛细管柱气相色谱起主导作用,固定液数量减少、质量提高,最常用的有五六种。到上世纪90年代以后固定相的研究以手性固定相和提高常规固定相的性能为主。进入21世纪,各个制备色谱柱的公司不断推出高性能、低流失、重复性好和专用型毛细管柱色谱柱,以适应研究和实际需要。     

Phase Distribution Chromatography (PDC) of Polystyrene

Abstract

Phase distribution chromatography is a new chromatographic method of fractionating polymers. The separation is achieved by partitioning the sample between the solvent and a polymer phase, in the case a noncross-linked polystyrene of very high molecular weight, which is coated as a thin layer on small glass beads. The temperature must be held below the θ-temperature of the sample. The separation increases sharply with decreasing temperature. The theory of this method is presented and compared with experimental results. The agreement is very good.     

Microwave dielectric relaxation and molecular dynamics in binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol)s of varying molecular weight in dilute solution

Molecular dynamics of binary mixtures of poly(propylene glycol) (PPG) and poly(ethylene glycol)s (PEGs) of varying molecular weight due to molecular interactions, chain coiling and elongation in dilute solution under various conditions, ie varying number of monomer units of PEG, method of mixing of polymers and solvent environment, has been explored using microwave dielectric relaxation times. The average relaxation time τ_o, relaxation time corresponding to segmental motion τ₁ and group rotations τ₂, of a series of binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol) of varying molecular weight (ie PPG 2000 + PEG 200, PPG 2000 + PEG 300, PPG 2000 + PEG 400, and PPG 2000 + PEG 600 mixed by equal volume in the pure liquid states, and PPG 2000 + PEG 1500, PPG 2000 + PEG 4000 and PPG 2000 + PEG 6000 mixed equal weights in solvent) have been determined in dilute solution in benzene and carbon tetrachloride at 10.10 GHz and 35 °C. A comparison of the results of these binary systems of highly associating molecules shows that the molecular dynamics corresponding to rotation of a molecule as a whole and segmental motion in dilute solutions are governed by the solvent density when the solutes are mixed in their pure liquid state. Furthermore, the molecular motion is independent of solvent environment when the polymers are added separately in the solvent for the preparation of binary mixtures. It has also been observed that there is a systematic elongation of the dynamic network of the species formed during mixing of pure liquid polymers in lighter environment of solvent with increasing PEG monomer units, while the elongation behaviour of the same species in the heavier environment of carbon tetrachloride solvent is in contrast to the elongation behaviour of the polymeric species formed in pure PEG. The role of rotating methyl side‐groups in the PPG molecular chain has been discussed in term of the breaking and reforming of hydrogen bonds in complex polymeric species for the segmental motion. In all these mixtures, the relaxation time corresponding to group rotations is independent of the solvent environment and constituents of the binary mixtures. The effect of chain flexibility and coiling in these binary mixtures is discussed by comparing the relaxation times of the mixtures with their individual relaxation times in dilute solutions measured earlier in this laboratory. © 2001 Society of Chemical Industry     

PEG-ZnO-PP复合抗静电剂及其对聚丙烯纤维的改性

选用相对分子质量分别为10 000和20 000的聚乙二醇(PEG 10000,PEG 20000)与氧化锌(ZnO)、马来酸酐(MAH)混合,再与聚丙烯(PP)共混,制备复合抗静电剂(PEG-ZnO-PP),然后将其与PP共混纺丝,制得共混纤维。研究了PEG-ZnO-PP复合抗静电剂的流动性和热性能,考察了共混纤维的力学性能和抗静电性。结果表明:复合抗静电剂的流动性和热性能因PEG的相对分子质量不同而有所不同,含PEG 10000的复合抗静电剂的流动性能较好,且其熔融热焓、熔融结晶温度、结晶放热高于含PEG 20000的复合抗静电剂。共混纤维力学性能和静电半衰期随复合抗静电剂含量的增加而减小,含PEG 20000的共混纤维抗静电效果更好。