Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Polyisoprene Nanoparticles Prepared by Polymerization in Microemulsion  [PDF]
Y. Apolinar,L. F. Ramos,H. Saade,R. Díaz de León,R. G. López
Journal of Nanomaterials , 2010, DOI: 10.1155/2010/549264
Abstract: Batch polymerization of isoprene was carried out at in a normal microemulsion stabilized with sodium dodecyl sulfate and initiated with the redox couple tert-butyl hydroperoxide/tetraethylene-pentamine. Characterization by transmission electronic microscopy showed that polyisoprene nanoparticles with number-average diameter close to 20?nm were obtained. The low molecular weights obtained, as determined by gel permeation chromatography, were probably due to chain scission as inferred from the oxidative ambient at which polymerization was carried out. Microstructure calculated from infrared spectroscopy data indicates that the obtained polyisoprene contains around 80% total 1,4 units, which is in accordance with its glass transition temperature ( ) determined by differential scanning calorimetry. 1. Introduction An improvement in the toughness of glassy polymers can be achieved by dispersion of rubber particles into the polymer matrix [1–3]. According to the literature, rubber particles with diameters between 1 and 2? m give the best results in the preparation of high-impact polystyrene (HIPS) [4, 5]. Nevertheless, it has been reported that smaller rubber particles combined with large ones (diameter?>?1? m) lead to a greater increase in the HIPS toughness [6]. Polyisoprene (PI) is a polymer used for preparing micrometric rubber particles, which in turn are used for successfully increasing the glassy polymers toughness [7, 8]. On this basis, it has been thought that it would be interesting to evaluate the effect of PI nanoparticles for improving the toughness of some glassy polymers. However, the reports on synthesis of PI nanoparticles are very scarce. Only two reports were found describing the synthesis of PI nanoparticles [9, 10]. Cheong et al. polymerized isoprene in emulsions with low polymer content stabilized with different surfactants, using thermal and redox initiation systems and a very small concentration of tert-dodecyl mercaptan (t-DM) in order to enhance the entry efficiency of radicals into micelles and particles [9]. They obtained PI particles with diameters in the range of 35?nm –100?nm. Furthermore, when polymerizations were carried out at 25°C using redox systems, polymer gel content was zero in most cases. It is noticeable that polymerization times were very long (≈40?h) and that micrographs were not included in this report. On the other hand, Lorenz et al. [10] obtained PI particles between 80 and 200?nm when polymerizing isoprene at 72°C overnight in miniemulsions stabilized with various surfactants and only using thermal initiators.

SHEN Yinghua,ZHANG Aiqin,WU Genzhuang,ZHANG Xiangying,

高分子学报 , 2008,
Abstract: A cationic polyacrylamide was synthesized by polymerization of acrylamide and 2-(methacryloyloxy)-ethyltrimethylammonium chloride (AM/MADQUAT)in solution or by inverse microemulsion polymerization using (NH_4)_2S_2O_8/NaHSO_3 as redox initiator.The sequence distribution and composition distribution were calculated from monomer reactivity ratios of different polymerization methods.The results show that charge distribution is more uniform for the copolymer prepared in inverse microemulsion,and copolymer composition distribution is close to unity and maintains approximately at feed ratio.Furthermore,influence of the structure of cationic polyacrylamides on kaolinite flocs size,reduction of zeta potential and flocs compressive yield stress has been investigated at pH 7.The results show that the kaolinite flocs size is strongly dependent upon copolymer microstructure; with greater flocs size being observed for copolymer prepared in inverse microemulsion than for that in solution.Copolymer microstructure has a marked effect on the zeta potential,whose decrease in magnitude was much greater in the presence of copolymer prepared in inverse microemulsion than that in solution.Greater compressive yield stress was achieved for the strong flocs produced by copolymer prepared in inverse microemulsion.The difference in flocs compressive yield stress may be attributed to the flocs structure.Therefore,in this paper,a strong correlation between the cationic polyacrylamide structure and flocculation property for kaolinite suspension was established.

ZHANG Zhi-cheng,XU Xiang-ling,ZHANG Man-wei,

高分子学报 , 1995,
Abstract: he acrylamide microemulsion at appropriate Span 20, Tween 60 and acrylamide concentration were biscontinuous ones demonstrated by the study on the microemulsion conductance. It was proved by conductance change during polymerization that the transistion from the biscontinous microemulsion to W/O one starts at the begining of polymerization and stops at the begining of constant polymerization period.

ZOU You-si,PAN Rong-hua,

高分子学报 , 1988,
Abstract: This work deals with the group transfer polymerization (GTP) of methyl methacrylate and some acrylates, with ethyl 3-ethoxy-3-trimethylsiloxyacrylate (ETSA) as initiator and Et4NHF2 as catalyst. Monodisperse polymer with predetermined molecular weights can be obtained by adjusting the monomer/initiator ratio. "Auto-acceleration" can be avoided by decreasing the catalyst concentration.
The Cationic Ring-Opening Polymerization of Tetrahydrofuran with 12-Tungstophosphoric Acid  [PDF]
Ahmed Aouissi,Salem S. Al-Deyab,Hassan Al-Shahri
Molecules , 2010, DOI: 10.3390/molecules15031398
Abstract: The cationic ring-opening polymerization reaction of tetrahydrofuran at 20 oC was catalyzed by H3PW12O40·13H2O as solid acid catalyst. The effect of the proportions of acetic anhydride and catalyst, reaction time and support on the polymerization reaction was investigated. It has been found that the yield and the viscosity of the polymer depend on the proportion of acetic anhydride, the presence of the latter in the reactant mixture being required for the ring-opening. The catalytic activity of the alumina-supported heteropolyacid results showed that Br?nsted acid sites are more effective than Lewis ones for the cationic ring-opening polymerization.
Reactivity of Heteropolymolybdates and Heteropolytungstates in the Cationic Polymerization of Styrene  [PDF]
Ahmed Aouissi,Zeid Abdullah Al-Othman,Holeil Al-Anezi
Molecules , 2010, DOI: 10.3390/molecules15053319
Abstract: The two heteropolyacids H3PW12O40 and H3PMo12O40, and their homologous salts (NH4)3PW12O40, and (NH4)3PMo12O40 were prepared and tested in the cationic polymerization of styrene. The results showed that the heteropolytungstates were more reactive than the heteropolymolybdates. It has been found that the yield and the viscosity averagemolecular weight (Mv) of polystyrene are directly proportional to the acidity strength of the heteropolyanions (H3PW12O40 > H3PMo12O40 > (NH4)3PW12O40 > (NH4)3PMo12O40). The highest yield (68.0%) and Mv (7,930) were obtained by using H3PW12O40. In addition, H3PW12O40 polymerized the styrene under mild conditions and was recyclable, and could behave as a truly heterogeneous catalyst.
Yufeng Wang,Kefu Chen,Lihuan Mo,Huiren Hu
BioResources , 2011,
Abstract: A cationic polyacrylamide (CPAM) dispersion, the copolymer of acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (DAC), has been synthesized through dispersion polymerization in aqueous ammonium sulfate ((NH4)2SO4) solution. The polymerization was initiated by tert-butyl hydroperoxide (TBHP) and ferrisulfas (FeSO4) using poly(dimethyl diallyl ammonium chloride) (PDMDAAC) as the stabilizer. At the optimal reaction conditions, the relative molecular weight of the CPAM dispersion was 4.2×106, its charge density was 2.2 mmol g-1, its average particle size was 6.01 μm, and its stability and dissolvability were both excellent. The CPAM dispersion was characterized using Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and differential scanning calorimeter (DSC). Results indicated that the copolymerization was successful.
Emulsion Polymerization of Vinyl Acetate in the Presence of a New Cationic Surfactant  [PDF]
Ayfer Sarac, Bahire Filiz Senkal, Murat Y?ld?r?m
American Journal of Analytical Chemistry (AJAC) , 2014, DOI: 10.4236/ajac.2014.51003

In this study, the emulsion homopolymerization system containing vinyl acetate, potassium persulfate, a new cationic polymeric surfactant and water was studied by the applying semi-continuous emulsion polymerization process. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate latexes were investigated depending on vinyl acetate percentage in the polymerization recipe, and two thermal initiators in homopolymerization.

Nanostructured Microemulsion Phase Behavior Using AOT or Extended Surfactant Combined with a Cationic Hydrotrope  [PDF]
Khalid Kanan, Hala Yousef, Ibrahim Kayali
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2012, DOI: 10.4236/jsemat.2012.21010
Abstract: The phase behavior for systems containing sodium bis (2-ethylhexyl sulfosuccinate) (AOT), with the cationic hydro-trope tetraethyl ammonium chloride (TEAC), in the presence of water and heptane were studied. Formulations of mi-croemulsion for such systems and for systems containing the so called “extended surfactant” were carried out at different salt concentrations. Anisotropy was detected using cross polarizers and polarized microscopy. Ultralow interfacial tension for microemulsion was measured, first theoretically using the Chun-Huh equation, and then experimentally using spinning drop experiments. The presence of short chain hydrotropes (TEAC) was found to destabilize the liquid crystalline region, observed in the AOT/water/heptane phase diagram. Ultralow interfacial tensions were observed for microemulsions formulated with surfactant concentrations as low as 0.5%, for both AOT and “extended surfactant” systems. The effect of temperature on the phase behavior of a microemulsion formed with AOT system was studied and found to behave in an opposite manner compared to the nonionic surfactant.
Cationic Polymerization of 1,2-Epoxypropane by an Acid Exchanged Montmorillonite Clay in the Presence of Ethylene Glycol  [PDF]
Ahmed Yahiaoui,Mohammed Belbachir,A?cha Hachemaoui
International Journal of Molecular Sciences , 2003, DOI: 10.3390/i4110572
Abstract: The polymerization of propylene oxide (PO) catalysed by maghnite-H+ (mag-H+) in the presence of ethylene glycol was investigated. Mag-H+ is a montmorillonite silicate sheet clay was prepared through a straight forward proton exchange process. It was found that the cationic polymerization of PO was initiated by mag-H+ at 20 °C both in bulk and in solution. The effect of the amount of mag-H+ and solvent was studied. These results indicated the cationic nature of the polymerization A possible initiation pathway, via the transfer of protons from mag-H+ to the monomer, is proposed.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.