Pedro Ivo C. Guimarães

CHEMICAL MODIFICATION OF CROSS-LINKED RESIN BASED ON ACRYLONITRILE FOR ANCHORING METAL IONS

Abstract Network resin based on acrylonitrile has been chemically modified through different reactions to obtain different chelating groups. The beads of resin were synthesized by aqueous suspension copolymerization of acrylonitrile (AN) and divinylbenzene (DVB). The chemical modifications of these beads’ cyano groups were carried out by reaction with hydroxylamine, hydrazine and ethanolamine producing amidoxime, amidrazone and oxazoline groups, respectively. The copolymer and modified resins were characterized by apparent density, surface area, average pore diameter, elemental analysis (CHN), FTIR and optical and electronic microscopies. Qualitative experiments of adsorption were conducted to evaluate the resins (modified and unmodified) on fixing Hg(II), Cd(II), Cu(II), Zn(II), Cd(II), Co(II), Ni(II) and Pb(II) from aqueous solution using batch extractions. Based on the results obtained, it was concluded that it is possible to modify chemically a resin containing cyano groups by different routes and to use these resins as a very low cost effective sorbent for metal ions.

Synthesis of crosslinked resin based on methacrylamide, styrene and divinylbenzene obtained from polymerization in aqueous suspension

Abstract A series of porous copolymer beads based on methacrylamide (MA), styrene and divinylbenzene (DVB) was prepared by aqueous suspension polymerization in the presence of diluents to act as precipitants. As MA is totally soluble into aqueous phase, the use of two types of phase transfer agent was investigated, namely: TritonX-100TM [polyoxyethylene-(10)-isooctylphenyl-ether] and tetrabutylammonium perchlorate. The effect of the diluents on the surface appearance and the porous structure of copolymer beads was studied. Suitable particle stabilisation was achieved by using a combination of two suspension agents, namely: gelatin and 2-hydroxy-ethyl-cellulose. The network resins were characterized by optical and scanning electron microscopy, IR spectroscopy, elemental analysis (CHN), apparent density, swelling in different solvents and specific area by BET method. It was observed that the MA incorporation was more effective when TritonTM was employed as phase transfer agent.

Microscopic analysis of porosity of 2-vinylpyridine copolymer networks. 1. Influence of diluent

The porous structure of copolymer networks based on 2-vinylpyridine, styrene and divinylbenzene at varied proportions prepared by suspension polymerization was varied by using different kinds of porogen agent, namely toluene, n-heptane, ethyl acetate. The materials were characterized by determination of surface area, average pore diameter and pore volume by BET/BJH, apparent density, elemental analysis (CHN) and swelling degree. Their morphologic characteristics were evaluated by microscopic analyses and correlations among porous structures and reaction parameters were found. It was noted that all synthesized resins have presented narrow particle size distributions; their porosities and visual appearances were dependent on the type and dilution of solvent employed in their syntheses.

Mutagenic risks induced by homemade hair straightening creams with high formaldehyde content.

Regardless of official recommendations, the inappropriate use of homemade hair creams has became a popular practice in Brazil and high formaldehyde content in the ‘progressive straightening’ creams has been reported. In the present work, three of these creams were analyzed by spectrophotometric, chromatographic and genotoxic assays in order to evaluate mutagenic risks associated with the uncontrolled addition of formaldehyde at contents higher than those allowed by regulation. The ultraviolet and Fourier‐transformed infrared absorption spectra showed characteristic signals that can be assigned to formaldehyde, although with different relative intensities, revealing distinct compositions. Using high‐performance liquid chromatography 1.6–10.5% w/v formaldehyde was quantified. Antibacterial activity was detected in all creams. At 0.10 μg per plate, one of them showed positive mutagenicity induction (P < 0.05) in the Salmonella/microsome assay using the TA100 strain. The measurement of β‐galactosidase induction in the SOS chromotest by this cream, at dosages of 10–100 μg per assay, was positive (P < 0.05) in Escherichia coli PQ37 and OG100 strains. Our data show a more intense genotoxic response than those reported before for formaldehyde, suggesting that this compound may be acting synergistically with any unknown components in the creams or perhaps these unspecified components by themselves might have significant genotoxic potential. We call attention to the popular use of homemade formulations of cosmetics, such as hair straightening creams, because they can contain mutagens that could increase the incidence of neoplasia in those people who use them. Copyright

Comparative study of homogeneous and heterogeneous styrene polymerizations with Ni(acac)2/MAO catalytic system

Abstract Styrene polymerization was carried out with Ni(acac) 2 /MAO and Ni(acac) 2 /SiO 2 /MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type.

Utilização de NBR Modificada com Grupos 2-Oxazolina em Misturas de NBR/EVA

Nitrile rubber/ethylene-vinyl acetate copolymer (NBR/EVA) blends with ratio of 70/30 wt% were prepared in the presence of functionalized NBR with 2-oxazoline groups. This functionalized copolymer was employed alone or in combination with EVA copolymer functionalized with hydroxyl, carboxyl or mercaptan groups. The reaction between the functional groups was confirmed by FTIR analysis of the unvulcanized samples insoluble fraction, and by the decrease in the tan d values. The mechanical properties were not substantially affected by the presence of these functionalized copolymers, probably due to the proportion of blend composition (with high amount of NBR), thus forcing the location of functionalized NBR inside the elastomer phase.

Emprego de catalisadores à base de níquel para homo- e copolimerização de estireno

This review deals with the homo- and copolymerization of styrene with nickel catalysts. The catalytic activity, polymer stereoregularity, polymer molecular weight and polydispersity are dependent upon nickel ligands and reaction parameters. Catalysts supported on silica, treated with methylaluminoxane (MAO), have shown higher stereospecificity and activity compared to homogeneous ones. The influence of these parameters is discussed focusing on the elucidation of some aspects of the polymerization mechanism.

Estudo da influência dos iniciadores na polimerização da 2-fenil-2-oxazolina

2-Phenyl-2-oxazoline was polymerized using methyl iodide, methyl tosilate, etherate boron trifluorated, dimethyl, diethyl and di-sec-butyl sulphate as initiators. The main aim of this work was to study the influence of type of initiator on the initiation and propagation processes as well the reactional conditions of these polymerizations. The polymerizations results showed that the nucleophilicity of initiator and different alkyl groups present in the dialkyl sulphates affect the initiation reaction, and influence the propagation species due to the counteranion effect, derived from these initiators. The dialkyl sulphates investigated exhibited good initiator efficiency and their performances were close.