Leonardo C. Ferreira

Synthesis, structural and spectroscopic studies of novel azo-containing N,O-bonded complexes in the α-Iminoketone and Azophenolate forms

This article describes the synthesis and the spectroscopic and structural characterization of two novel azo-containing complexes, cis-bis[4-nitro-2-(4-nitrophenylazo)-phenolate-κN1]bis(piridino-κN)cadmium(II), 1, and cis-bis[2-(4-phenylazo-phenylimino)-2H-acenaphthylen-1-one]dichloromercury(II), 2. In spite of the different metal centres, both complexes show an N,O-bidentate complexation to the metal. In 1 the metal coordinates to an azo N and to a phenolate O atom, whereas in 2 the metal binds to an O and an N atom of the α-iminoketone. Both complexes show intramolecular π-π interactions, which play an important role in their molecular structures. In addition they also present non-classical H-bonding, which is crucial to their supramolecular arrangements. Moreover, 2 is the first case in the literature of a complex with a new class of ligand, an azoiminoketone, as well as the first case of an α-iminoketone Hg complex.

Poly(lactic acid)/Cellulose Composites Obtained from Modified Cotton Fibers by Successive Acid Hydrolysis

This work is focused on the hydrolysis of cotton fibers from waste textiles to obtain micro and nanofibers to be used as reinforcements in polymer composites. To promote their compatibility with polymeric matrix, hydrolyzed cotton fibers were surface modified with various silane compounds. Thus, these fibers were mixed with commercial poly(lactic acid) (PLA) at 5% w/w loading by melt compounding. Acid treatments caused a decrease of the crystallinity index whereas the thermal stability was significantly improved, especially for cellulose fibers hydrolyzed in two steps. Morphological analysis revealed a reduction of the fibers diameter and a decrease of their length as a consequence of the hydrolysis. NMR analysis confirmed the silanization of the fibers by reaction with the silane agent. Tensile tests revealed that silanization treatments were able to increase the composite Young’s modulus and the stress at break with respect to the neat matrix, indicating that silanization improved the polymer/fiber compatibility interfacial adhesion. The overall results demonstrated that applying suitable surface modification strategies, waste cotton textiles can be effectively recycled as fillers in polymer based composites.

Synthesis and Application of Bimetallic Zinc(II) Phenoxy-Imine Complexes as Initiators for Production of Lactide Polymers

This article reports the synthesis of two bimetallic zinc(II) complexes containing phenoxyimine ligands and their application as initiators of ring opening polymerization (ROP) of L-lactide (LA). The phenoxy-imine ligands were obtained from salicylaldehyde derivatives and 2,3,5,6-tetramethylphenylenediamine, yielding two bidentate regions per ligand. The reactions of both phenoxy-imine ligands with ZnEt2 in the presence of n-BuOH afforded [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2], which were characterized by elemental analysis, Fourier transform infrared (FTIR) and H nuclear magnetic resonance (NMR) spectroscopy. In addition, the geometries of both complexes were investigated by DFT (B3LYP/LACVP**) calculations. [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2] were tested as initiators of ROP of LA at 180 °C using different LA/Zn molar ratios, namely 500, 1000 and 2500. Both complexes showed good activity, resulting in conversions up to 96% in 2 h. The poly-LLA exhibited average molecular weight (Mw) ranging from 45,000-92,000, relatively low polydispersity (Mw/Mn = 1.6-2.0) and high stereoregularity with melting temperature Tm = 164 °C.

ESTUDO DE INCORPORAÇÃO DE NANOCARGAS DE SIC À MATRIZ DE POLI(METACRILATO DE METILA) VIA POLIMERIZAÇÃO EM MASSA

Flávio James Tommasini Leonardo da Cunha Ferreira Sergio Neves Monteiro Matheus R Affonso Victor S Brandão Caio V C Lira Pedro H L M Lopes Resumo A pesquisa foi realizada com o intuito de produzir nanocompósitos baseados em uma matriz polimérica de poli (metacrilato de metila) (PMMA) com nanocargas de carbeto de silício (SiC) dispersas na matriz orgânica. Os nanocompósitos foram produzidos através da polimerização em massa, a qual o peróxido de benzoíla foi utilizado como o iniciador. Os novos materiais foram produzidos sob a forma de filmes e consequentemente eles foram submetidos e caracterizados pelas análises de termogravimetria (TGA), espectroscopia de infravermelho por transformada Fourier (FTIR), fluorescência de raio-x (XRF), espectroscopia por energia dispersiva de raio-x (EDS) e microscopia eletrônica de varredura (FEGSEM). Os resultados obtidos durante a caracterização dos filmes dos nanocompósitos demonstraram a boa eficiência dos processos de sínteses e misturas das cargas de SiC na matriz orgânica. Palavras-chave: Nanocompósitos; Carbeto de Silício; Poli (metacrilato de metila); Polimerização em Massa; Filmes Planos.

cis-Bis{(E)-2-[(2-fluoro­phen­yl)imino­meth­yl]phenolato-κ2N,O}bis­(pyridine-κN)nickel(II)

The structure of the title compound, [Ni(C13H9FNO)2(C5H5N)2], consists of an NiII atom on a crystallographic center of symmetry, octahedrally bonded through both the N and O atoms to two 2-[(2-fluorophenyl)iminomethyl]phenolate (L) ligands, as well as two pyridine ligands. The F atoms of L are disordered over two positions related by a 180° rotation of the fluorophenyl group around its external C—N bond.

1,2-Bis(2-tert-butylphenylimino)-1,2-dihydroacenaphthylene

The crystal structure of the title compound, C32H32N2, reveals a dimeric association of -diimine units into centrosymmetric dimers via intermolecular non-classical C—H N hydrogen bonds. There is also intramolecular non-classical C—H N bonding between the methyl groups and the N atoms of the diimine unit. In addition, the crystal packing indicates – interactions between acenaphthylene rings [3.888 (7) Å]. The deviation from a planar arrangement of the molecule can be attributed to both interand intramolecular non-classical hydrogen bonding.

2-(2,6-Diisopropyl­phenyl­imino)-1-phenyl­propan-1-one

In the crystal structure of the title compound, C20H25NO, all bond lengths and angles show normal values. Non-classical hydrogen bonds are responsible for the deviation from a planar arrangement.