Mechanism of simultaneous solutes separation and concentration by size exclusion cyclic separation

The semicontinuous separation/concentration of two solutes with different molecular size by the size exclusion cyclic separation method is based on the opposite swelling responses of two gels to a temperature change. Experimental results of separation and concentration of solutes are verified qualitatively by the theoretical models based on the local equilibrium assumption. Separation of two solutes is shown by the breakthrough curves in coupled gel columns. In closed coupled columns, the volumetric space for the large molecules which are totally excluded from the gels becomes smaller, creating a concentrating effect as the gels swell when temperature changes. A mechanistic model is suggested to predict the large molecule concentration to increase to its solubility limit as cycle repeats.     

采用负离子原位聚合法制备聚丁二烯/二氧化硅纳米复合材料

采用负离子原位聚合工艺制备了聚丁二烯(PB) /SiO2纳米复合材料,研究了复合材料的结构及性能。结果表明,经过γ-(甲基丙烯酰氧基)丙基三甲氧基硅烷(MPS)处理后的SiO2粒子与PB基体形成了强烈的界面相互作用,使得复合材料的玻璃化转变温度(Tg)升高,热稳定性提高,储能模量(E′)明显增大,损耗因子(tanδ)降低。     

Polyamide 6/silica nanocomposites prepared by in situ polymerization

A polyamide 6 (PA 6)/silica nanocomposite was obtained through a novel method, in situ polymerization, by first suspending silica particles in ϵ-caproamide under stirring and then polymerizing this mixture at high temperature under a nitrogen atmosphere. The silicas were premodified with aminobutyric acid prior to the polymerization. The effects of the addition of unmodified and modified silicas on the dispersion, interfacial adhesion, isothermal crystallization, and mechanical properties of PA 6 nanocomposites were investigated by using scanning electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, and mechanical tests, respectively. The results show that the silicas dispersed homogeneously in the PA 6 matrix. The addition of silicas increases the glass transition temperature and crystallization rate of PA 6. The mechanical properties such as impact strength, tensile strength, and elongation at break of the PA 6/modified silica nanocomposites showed a tendency to increase and decrease with increase of the silica content and have maximum values at 5% silica content, whereas those of the PA 6/unmodified silica system decreased gradually. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 355–361, 1998     

Pore size control of porous silica by sol-gel process

Porous silica glass was prepared by sol-gel process from tetraethoxysilane (TEOS). The effects of solvents (water, ethanol), drying condition, heat treatment temperature on specific surface area and pore size distribution of porous silica were investigated. Gelation process accelerates with an increase of H₂O content, while retards with the increase of ethanol amount. Structure changes during heat treatment were studied by means of DTA, XRD. TEM micrographs show that the gel particles shrink after heated at 500°C, thus the average pore size decreases.     

Synthesis of star polymers by organized polymerization of macromonomers

Vinylbenzyl-terminated polyisoprene (PI) macromonomers were synthesized by the coupling reaction of the corresponding living anions with p-chloromethylstyrene. PI stars were prepared by the free-radical crosslinking of PI macromonomers with divinylbenzene (DVB) in n-heptane. No macrogelation was observed during polymerization. The radical copolymerization of PI macromonomer with DVB led to microgelation in micelles formed by PI macromonomers in the selective solvent (organized polymerization). The arm number of star polymers depended strongly on the concentration ratio of DVB to macromonomer ends.     

Pore size evaluation for fine porous freeze-dried cellulose acetate membrane by gas separation

The pore size for a fine porous freeze-dried cellulose acetate membrane was evaluated by gas separation methods, where the Present–deBethune equation was applied. Separation coefficients were referred to the calculated value for each pore size from this equation. Nuclepore, Millipore VS, and Millipore VC, whose pore sizes were already known by bubble point method, were tested for this method. Pore diameters for this cellulose acetate membrane, thus determined, were about 25 and 40 Å from Ar–Kr and N₂–Kr separation systems, respectively, which agreed well with the results from electron microscope (50 Å) and N₂ gas permeability (50 Å). However, it is impossible to apply this method to He gas separation, since He gas permeability is higher than the expected value as Knudsen flow, which indicates that some channels are existing in this membrane, where He gas is more permeable than the other gases.     

In situ synthesis of porous silica nanoparticles for covalent immobilization of enzymes

A simple method is used to covalently encapsulate enzymes in silica nanoparticles. The encapsulation is highlighted by the high enzyme loading and porous channels that provide efficient diffusion for small substrate and product molecules while preventing protease degradation.     

Chromatogram broadening of proteins and dextrans in size exclusion chromatography

The mechanisms governing the broadening of experimental chromatograms for proteins and paucidisperse dextrans were studied on TSK-G2000SW and TSK-G3000SW columns. Within the conditions studied, the chromatogram variance for all solutes increased linearly with increasing effluent flow rate. As predicted by current theories of the kinetics of size exclusion chromatography, this flow rate dependence is caused mainly by slow mass transport of the solute within the stationary phase of the column. Restricted diffusion within the stationary phase was dependent upon the ratio of solute molecular size to column pore radius and was similar for both proteins and dextrans. In comparison with results for monodisperse proteins, the broader chromatograms produced by dextrans were due to sample polydispersity and not to differences in solute column spreading. Corrections for column spreading on these columns are small for the determination of integral properties of polymers but may be significant when molecular weight distributions are of interest.     

trans-polyisoprene/multi-walled carbon nanotubes/silica nanocomposites prepared by in situ Ziegler-Natta polymerization

<正>This paper reports the first example of preparation of trans-polyisoprene (TPI)/multi-walled carbon nanotubes (MWCNTs)/silica(SiO_2) nanocomposites via in situ Ziegler-Natta polymerization. A TiCl_4 of Ziegler-Natta catalyst species was incorporated into MWCNTs/SiO_2/MgCl_2 carrier via surface functional groups including     

Coating of porous silica beads by in situ polymerization/crosslinking of 2‐hydroxypropyl β‐cyclodextrin for reversed‐phase high performance liquid chromatography applications

Porous silica beads were coated with a crosslinked β‐cyclodextrin polymer by in situ polymerization/crosslinking of 2‐hydroxypropyl β‐cyclodextrin with 1,6‐hexamethylenediisocyanate in anhydrous dimethylsulfoxide. This method was developed for the preparation of reversed‐phase high performance liquid chromatography stationary phases. The mass of polymer immobilized onto the silica surface was controlled by the amount of coupling agent, 1,6‐hexamethylenediisocyanate, added during the coating process. The influence of the polymer coating on the physical features of the beads was investigated by means of nitrogen adsorption/desorption methods, scanning electron microscopy and energy dispersion X‐ray analysis. The column lifetime was found to be primarily dependent on the extent of crosslinking of the stationary phase. Moreover, it was demonstrated that the synthesis of highly crosslinked stationary phases with a reasonable column lifetime gave rise to a phase separation of the β‐cyclodextrin polymer. To prove their usefulness as reversed‐phase packing materials, they were used to separate mixtures of nitrophenol positional isomers, four pesticides, and drugs. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1419–1426, 2004     

Study of metallocene supported on porous and nonporous silica for the polymerization of ethylene

Aromatization and isomerization of n- hexane catalyzed by Pt/zeolite were investigated. For Pt/K- β and Pt/K-mordenite as well as for Pt/K-L, the addition of KCl resulted in an increase in selectivity for benzene formation accompanied with a decrease in selectivity for hydroisomerization. A parallelism was found between changes in the benzene selectivity with the KCl addition and in the terminal cracking index. The treatment of Pt/K-FSM-16 with K₂CO₃ resulted in a decrease in cracking products and an increase in benzene selectivity. At 523 K, Pt/H- FSM-16 catalyst showed high selectivity for methylcyclopentane and cyclohexane. At 623 K, it showed high and durable isomerization activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of acrylonitrile polymerization on the surface of porous microspherical silica gel

The kinetics of acrylonitrile polymerization on the surface of porous microspherical silica gel (PMSS) was studied and some kinetic parameters were determined. The structure of PMSS-based sorbents was analyzed by FTIR-spectroscopy, XRD and sorption analysis before and after microcapsulation with polyacrylonitrile.     

Synthesis of low molecular weight-hydroxy polycaprolactone macromonomers by coordinated anionic polymerization in protic conditions

This article reports the development of a new catalytic process that takes advantage of the exchange reaction between aluminium alkoxides and alcohols to obtain functionalized low molecular weight oligomers by anionic ring-opening polymerization. The aluminium alkoxides can be used in homogeneous medium or grafted on a porous support to make possible a heterogeneous process. ω-Hydroxy oligo polycaprolactones macromonomers with 2-hydroxyethylmethacrylate or hydroxymethylstyrene as polymerizable end groups have been synthesized and characterized by NMR and SEC. Mass spectrometry (LSIMS) has been used in an attempt to determine the MWD. These macromonomers have been engaged in copolymerization with styrene and the reactivity ratios have been approached. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2357–2372, 1997     

Hybrid poly(ethylene terephthalate)/silica nanocomposites prepared by in‐situ polymerization

The nanocomposites, based on hybrid poly(ethylene terephthalate) (PET)/silica nanoparticles, were prepared via in‐situ condensation polymerization of terephthalic acid and ethylene glycol in the presence of silica nanoparticles pretreated with a silane coupling agent. Such a polymerization process ensured that the silica nanoparticles were well dispersed in PET matrix with the size ranging from 40 to 60 nm, which was confirmed by transmission electron microscope (TEM) observation. Attributed to the unique bonding between SiO₂ nanoparticle and PET, the crystallization behavior of PET was improved significantly, at a low temperature in particular. To further explore the effects of silica nanoparticles on crystallization, extensive differential scanning calorimeter (DSC) measurements were performed in an attempt to reveal the impact of the morphology of the dispersed silica nanoparticle (i.e., sphere or gel‐like) on the peak temperature during melting as well as the amount of heat involved in crystallization. The influences of the structure of polyether glycol (PEG) used for PET preparation as well as the addition of glass fibres (GF) were also investigated using DSC. It was concluded that the synergy among silica nanoparticles, modified PEG, and GFs lowers both T_g and T_m of PET, thus facilitating the injection processes in application. POLYM. COMPOS. 28:42–46, 2007. © 2007 Society of Plastics Engineers     

Preparation and properties of nylon 6/carboxylic silica nanocomposites via in situ polymerization

Nylon 6/carboxylic acid‐functionalized silica nanoparticles (SiO₂‐COOH) nanocomposites were prepared by in situ polymerization of caprolactam in the presence of SiO₂‐COOH. The aim of this work was to study the effect of carboxylic silica on the properties of the nylon 6 through the interfacial interactions between the SiO₂‐COOH nanoparticles and the nylon 6 matrix. For comparison, pure nylon 6, nylon 6/SiO₂ (unmodified) and nylon 6/amino‐functionalized SiO₂ (SiO₂‐NH₂) were also prepared via the same method. Fourier transform infrared spectrometer (FTIR) spectroscopy was used to evaluate the structure of SiO₂‐COOH and nylon 6/SiO₂‐COOH. The results from thermal gravimetric analysis (TGA) indicated that decomposition temperatures of nylon 6/SiO₂‐COOH nanocomposites at the 5 wt % of the total weight loss were higher than the pure nylon 6. Differential scanning calorimeter (DSC) studies showed that the melting point (T_m) and degree of crystallinity (X_c) of nylon 6/SiO₂‐COOH were lower than the pure nylon 6. Mechanical properties results of the nanocomposites showed that nylon 6 with incorporation of SiO₂‐COOH had better mechanical properties than that of pure nylon 6, nylon 6/SiO₂, and nylon 6/SiO₂‐NH₂. The morphology of SiO₂, SiO₂‐NH₂, and SiO₂‐COOH nanoparticles in nylon 6 matrix was observed using SEM measurements. The results revealed that the dispersion of SiO₂‐COOH nanoparticles in nylon 6 matrix was better than SiO₂ and SiO₂‐NH₂ nanoparticles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal crystallization kinetics and melting behavior of polyamide 11/silica nanocomposites prepared by in situ melt polymerization

Polyamide 11 (PA 11)/silica nanocomposites were prepared via in situ melt polymerization by the dispersion of hydrophobic silica in 11‐aminoundecanoic acid monomer. Their isothermal crystallization process and melting behaviors were analyzed by differential scanning calorimetry. The isothermal crystallization kinetics was analyzed by the Avrami equation. The obtained data showed that the model of nucleation and growth of PA 11 was not affected after the incorporation of silica and was a mixture with two‐dimensional, circular, three‐dimensional growth with thermal nucleation. Double and single melting peaks were observed depending on the crystallization temperature. The equilibrium melting point of samples was evaluated, and the spherulites growth kinetics parameters and fold surface free energy were further calculated according to the classical theories. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of polytetrahydrofuran monomethacrylate macromonomers by cationic ring‐opening polymerization of tetrahydrofuran

Polytetrahydrofuran monomethacrylate (MA‐PTHF) macromonomer was prepared by cationic ring‐opening polymerization(CROP) of tetrahydrofuran (THF) using boron trifloride etherate (BF₃ · OEt₂) as initiator and epichlorohydrin (ECH) as promoter. Two kinds of transfer agents were used: methacrylic acid (represented as TA1), and a mixture of methacrylic acid and sodium methacrylate (represented as TA2). The effects of polymerization conditions on molecular weight and molecular weight distribution of macromonomers were studied in this article, when the composition of reactants was kept constant. Under the same conditions, the molecular weight of macromonomer using TA2 is lower than that using TA1, which indicates that TA2 is more active than TA1. The molecular weight of MA‐PTHF macromonomer varies with the polymerization time before transfer agents were added (T1), but molecular weight distribution remains constant. When T1 is limited in 30 min, the apparent number‐average molecular weight of MA‐PTHF increases significantly with the increase of T1, and ranges from 5000 to 18,000. Hence, the molecular weight of MA‐PTHF macromonomer can be controlled by varying T1. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 810–815, 2000     

Characterization of block copolymers by size exclusion chromatography

Summary Poly(ethyl methacrylate-b-deuterated methyl methacrylate), poly(styrene-b-methyl methacrylate), and poly(styrene-b-dimethylsiloxane)diblock copolymers have been characterized by means of size exclusion chromatography (GPC) apparatus fitted with four detectors in series, viz continuous viscometer, UV spectrophotometer, low angle light scattering photometer, and differential refractometer. The continuous measurements of the scattered light intensity, the limiting viscosity number, the concentration, and the chemical composition permits complete determination of the molecular characteristics of block copolymers.