Search results for "polymerization"

Photo-polymerized lauryl methacrylate monolithic columns for CEC using lauroyl peroxide as initiator

2009

Lauryl methacrylate (LMA)-ester based monolithic columns photo-polymerized using lauroyl peroxide (LPO) as initiator were prepared, and their morphological and CEC properties were studied. The composition of the polymerization mixture (i.e. ratios of monomers/porogenic solvents, 1,4-butanediol/1-propanol and LMA/crosslinker) was optimized. The morphological and chromatographic properties of LMA columns were evaluated by means of SEM pictures and van Deemter plots of PAHs, respectively. The polymerization mixture selected as optimal provided a fast separation of a mixture of PAHs with excellent efficiencies (minimum plate heights of 8.9-11.1 μm). Satisfactory column-to-column (RS D < 4.5%) a…

Comparison on photo-initiators for the preparation of methacrylate monolithic columns for capillary electrochromatography.

2010

The synthesis of lauryl methacrylate monoliths for capillary electrochromatography by UV polymerization using several free-radical initiators (alpha,alpha'-azobisisobutyronitrile, 2,2-dimethoxy-2-phenylacetophenone, dibenzoyl peroxide (BPO) and lauroyl peroxide (LPO)) has been investigated. Using a 1,4-butanediol/1-propanol mixture as porogenic solvent, the influence of each initiator and its content on the morphological and electrochromatographical properties of beds was evaluated. Under their respective optimum content, satisfactory separations of a test mixture of PAHs with similar efficiencies (minimum plate heights of 8.0-12.7 microm obtained from Van Deemter plots) were achieved for t…

CEC column behaviour of butyl and lauryl methacrylate monoliths prepared in non-aqueous media

2009

Polymeric monolithic stationary phases for capillary electrochromatography were prepared using two bulk monomers, butyl methacrylate (BMA) and lauryl methacrylate (LMA), by in situ polymerization in non-aqueous media. The effect of 1,4-butanediol/1-propanol ratio on porous properties was investigated separately for each monomer, keeping the proportion of monomers to pore-forming solvents fixed at 40:60 wt:wt. Also, mixtures of BMA and LMA at different 1,4-butanediol/1-propanol ratios were studied for tailoring the morphological features of the monolithic columns. The chromatographic performance of the different columns was evaluated by means of van Deemter plots of polycyclic aromatic hydro…

Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand

2007

The direct reaction between [VCl(3)(thf)3] or [VO(OEt)3] and 2,2'-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol (tbopH(2)) leads to the formation of [V(2)(micro-tbop-kappa(3)O,S,O)2Cl(2)(CH(3)CN)(2)] (1).4CH(3)CN or [V(2)(micro-OEt)2(O)2(tbop-kappa(3)O,S,O)2] (2), respectively, in high yield. Compounds 1 and 2 were characterized by chemical and physical techniques including X-ray crystallography and variable temperature magnetic susceptibility studies (J = -29.1 cm(-1)) for 1. Complexes 1 and 2 were supported on MgCl2 and when activated with aluminium alkyls, were found to effectively polymerize ethene to produce polyethylene with a narrow molecular weight distribution M(w)/M(n) approximately…

Darstellung, eigenschaften und umsetzungen von polyvinylsulfofluoriden

1960

Vinylsulfofluorid wurde mit Azo-bis-isobutyronitril polymerisiert. Es wurden Polymerisationsgrade bis 390 erreicht. Die Molekulargewichte wurden durch Viskositatsmessungen an den durch Verseifung der Polyvinylsulfofluoride gewonnenen Natriumsalzen der Polyvinylsulfonsaure ermittelt. Die Polyvinylsulfofluoride wurden mit Ammoniak, aliphatischen und aromatischen Aminen umgesetzt. Dabei wurden Umsatze bis zu 80 Mol% erreicht. Vinylsulfofluoride was polymerized with azo-bis-isobutyronitrile. The degree of polymerisation was up to 390. The molecular-weights were determined by measuring the viscosity of the sodium-salts of polyvinylsulfonic acids obtained by saponification of polyvinylsulfofluori…

1967

Durch Viskositatsmessungen und spektroskopische Bestimmung des gebildeten Monomeren wird der saurekatalysierte Abbau von Poly-3,4-acrolein verfolgt. Er erfolgt fast ausschlieslich durch Kettenspaltung; eine Depolymerisation tritt nur in untergeordnetem Mase auf. Diese im Vergleich zu anderen polymeren Aldehyden unerwarteten Ergebnisse werden mit dem Auftreten eines durch Resonanz stabilisierten Kettenendes bei der Spaltung erklart. The acid-catalyzed degradation of poly-3,4-acrolein was investigated by viscosity and spectroscopic determination of the monomer formed. The degradation occurs predominantly by chain scission; depolymerization is of minor importance. The results are unexpected in…

Synthesis, characterization and ethylene polymerization by metallasilsesquioxane

2013

Soluble complexes of group (IV) metallocenes anchored on a substituted polyhedral oligomeric silsesquioxane trisilanol support were prepared and characterized. These catalyst precursors formulated as [M(O^O^O)X] are found to be active in polymerization of ethylene at high temperature in combination with ethylaluminum sesquichloride (Et3Al2Cl3, EASC) as co-catalyst. The polyethylene obtained by these catalysts is linear, crystalline and displays narrow dispersity. The unique low molecular weight PE formed in this reaction exhibits properties comparable to commercial micronized PE waxes that have potential industrial applications in surface coating and ink formulations. Copyright © 2013 John …

Molecularly imprinted polymer solid phase extraction of fungicides from wine samples

2014

In order to preconcentrate iprodione fungicide in white wine samples, molecularly imprinted polymers (MIPs) specific for iprodione were synthesized using two polymerization approaches: precipitation (MIPp) and bulk polymerization (MIPb). A comparison of the performance of the MIPs and the corresponding non-imprinted polymers (NIPs) was conducted in batch studies. In this case, the MIPp revealed better recognition properties toward iprodione in wine samples than the MIPb. The MIPp and MIPb were then used as sorbents on solid phase extraction cartridges (MISPEp and MISPEb consecutively) in order to pre-concentrate iprodione from white wine samples. The optimization of the MISPE elution step w…

Color stability of Bulk-Fill composite restorations

2020

Made available in DSpace on 2022-04-28T19:29:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-11-01 Background: The color stability of the composite resin is an important property that influences its clinical longevity, which remains an inherent challenge to the material. Thus, the purpose of this study was to evaluate the color stability of bulk-fill resins when exposed to dye. Material and Methods: Cavities were prepared in 80 bovine incisors, which were randomly assigned into 4 groups (n = 20) according with the resin composite used: P60 (Control Group - Filtek P60, 3M/ESPE), FP (Filtek Bulk-Fill Posterior, 3M/ESPE), SDR (SDR, Dentsply) and FF (Filtek Bulk Fill Flow, 3M/ESPE). A…

D2 and H2 adsorption capacity and selectivity in CHA zeolites: Effect of Si/Al ratio, cationic composition and temperature

2020

International audience; The work deals with the effect of composition of CHA zeolites on the adsorption and separation of H2 and D2 under cryogenic temperatures. In the first part of this work the effect of Si/Al ratio and cationic composition on single gas adsorption of H2 and D2 was studied at 77.4 K. It was found that the adsorption capacities increase with Al content up to Si/Al = 2.1. Unexpectedly, Na-CHA zeolite with the highest Al content (Si/Al = 1.1) adsorbs only negligible amount because of the collapse of the zeolite structure upon dehydration at 400°C. The Na-and Li-containing chabazites with Si/Al = 2.1 possess similar adsorption capacities. In contrast, progressive replacement…