138 research outputs found

    Synthesis of polyethylene/starch hybrids using aqueous mini emulsion polymerization

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    Sustainability regarding the most produced plastic, polyethylene, was the main motivation factor behind research of this thesis. The aim was to synthesize hybrids of polyethylene and starch in an aqueous mini emulsion polymerization process using single-site catalysts. Two types of water soluble starches were applied: potato and hydroxyethyl starch. A trifluoromethane bearing nickel enolate catalyst and a 5-halo 3-methoxy salicyl aldiminate nickel pyridyl catalyst (with Cl and Br as halogen atoms) were used as polymerization catalysts, the latter two known to results in higher molecular weight polymer. The first catalyst turned to be sufficiently active with increased loads of starch and resulted in hybrids containing between 7.5 and 92.3 % starch. The salicylaldiminate catalysts only led to traces of polyethylene since the applied ethylene pressure of ca. 7.5 bar in the glass reactor was not sufficiently high to polymerize in aqueous solution. The hybrids were characterized using IR spectroscopy, TGA, density measurements, DSC, SEM and TEM. For the determination of the starch content the aqueous latex samples had to be washed with acetone to remove the surfactant (sodium dodecyl sulfate,) and co-surfactant (hexadecane). The SEM and TEM showed that the starch was uniformly distributed in the hybrids. Biodegradability tests were carried out with three different types of fungi, Aspergillus, Trichoderma, and Myrothecium for 21 days. Aspergillus turned out to be the most active in the metabolization of the starches with hydroxymethyl starch being degraded more rapidly than potato starch. The biodegraded samples were also characterized by IR, TGA, and DSC and SEM, verifying that the starch and soap were metabolized by the fungi whereas the polyethylene was not. The crystallinity of the polyethylene was slightly increased as a result of the biodegradation

    The Halogen Effect on the Magnetic Behaviour of Dimethylformamide Solvates in [Fe(halide-salEen)2]BPh4

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    Funding Research was funded by Fundação para a Ciência e a Tecnologia (FCT): projects UIDB/00100/2020, UIDP/00100/2020, LA/P/0056/2020, UIDB/04046/2020, UIDP/04046/2020, UIDB/50006/2020, UIDP/50006/2020 and LA/P/0008/2020, UIDB/04378/2020, UIDP/04378/2020, and LA/P/0140/2020, PTDC/QUI-QFI/29236/2017, PTDCQUI-QIN0252_2021, CEECIND/00509/2017; Fonds de la Recherche Scientifique (FNRS): PDR T.0095.21); Portugal2020: CENTRO-01-0145-FEDER-000018; Royal Society of Chemistry (RSC): R21-7511142525. Acknowledgments Centro de Química Estrutural (CQE) and Institute of Molecular Sciences (IMS) acknowledge the financial support of Fundação para a Ciência e a Tecnologia (FCT): Projects UIDB/00100/2020, UIDP/00100/2020, and LA/P/0056/2020, respectively. BioISI acknowledges FCT for financial support (UIDB/04046/2020, UIDP/04046/2020). This work was supported by the FNRS (PDR T.0095.21). Clara S. B. Gomes acknowledges the Associate Laboratory for Green Chemistry—LAQV, the Applied Molecular Biosciences Unit—UCIBIO and Associated Laboratory i4HB, which are financed by national funds from FCT (UIDB/50006/2020, UIDP/50006/2020 and LA/P/0008/2020, UIDB/04378/2020 and UIDP/04378/2020, and LA/P/0140/2020, respectively). Sónia Barroso thanks project SmartBioR for financial support (CENTRO-01-0145-FEDER-000018)and Centro de Química Estrutural for the access to crystallography facilities. Nuno A. G. Bandeira gratefully acknowledges the NanoBioSolutions FCT grant PTDC/QUI-QFI/29236/2017 for the computational infrastructure. Paulo N. Martinho thanks FCT and RSC for financial support (grants PTDCQUI-QIN0252_2021 and R21-7511142525). Paulo N. Martinho also thanks FCT for the contract CEECIND/00509/2017.Complexes [Fe(X-salEen)2]BPh4·DMF, with X = Br (1), Cl (2), and F (3), were crystallised from N,N′-dimethylformamide with the aim of understanding the role of a high boiling point N,N′-dimethylformamide solvate in the spin crossover phenomenon. The counter ion was chosen for only being able to participate in weak intermolecular interactions. The compounds were structurally characterised by single crystal X-ray diffraction. Complex 1 crystallised in the orthorhombic space group P212121, and complexes 2 and 3 in the monoclinic space group P21/n. Even at room temperature, low spin was the predominant form, although complex 2 exhibited the largest proportion of the high-spin species according to both the magnetisation measurements and the Mössbauer spectra. Density Functional Theory calculations were performed both on the periodic solids and on molecular models for complexes 1–3 and the iodide analogue 4. While all approaches reproduced the experimental structures very well, the energy balance between the high-spin and low-spin forms was harder to reproduce, though some calculations pointed to the easier spin crossover of complex 2, as observed. Periodic calculations with the functional PBE led to very similar ΔEHS-LS values for all complexes but showed a preference for the low-spin form. However, the single-point calculations with B3LYP* showed, for the model without solvate, that the Cl complex should undergo spin crossover more easily. The molecular calculations also reflected this fact, which was more clearly defined when the cation–anion–solvate model was used. In the other models there was not much difference between the Cl, Br, and I complexes.publishersversionpublishe

    Transition metal complexes of N-heterocyclic carbenes and derivatives thereof: synthesis and reactivity study

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    N-heterocyclic carbenes (NHCs) have played a dominant role in organometallic chemistry for decades and revolutionized the field of homogenous catalysis. NHCs have been thoroughly studied, both experimentally and theoretically, and have shown unique reactivity towards transition metals, chalcogens, azides and pnictogens. This thesis is aimed at utilizing the unique reactivity of N-heterocyclic carbenes to develop novel, robust catalysts to mediate organic transformations. The multi-faceted work within this thesis explores the use of NHCs as ancillary ligands on early and late transition metals as potential catalysts for olefin polymerization and ring-closing metathesis, respectively. This work also includes exploring the synthesis and coordination of ancillary ligands derived from the unique reactivity of NHCs towards azides, chalcogens and pnictinidenes. The reactivity of a novel aryl-substituted acyclic imino-N-heterocyclic carbene to early transition metals, cyclooctasulfur and Grubbs-type ruthenium benzylidene complexes was explored. The reactivity of imidazol-2-imide towards Grubbs-type ruthenium benzylidene complexes and the synthesis and coordination of a novel group of ligands bearing an imidazol-2-imine scaffold were also explored. Lastly, this work will include the reactivity of IMes=PPh to Grubbs-type ruthenium benzylidene complexes

    Recent progress on nickel-based systems for ethylene oligo-/polymerization catalysis

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    Recent progress on nickel-based complex pre-catalysts is reviewed herein. The ethylene oligo-/polymerization behaviour is discussed in terms of the variation of the complex models bearing different kinds of ligand sets. These discussions focus mainly on the influence that the different substituents present have on the observed catalytic activity, the results of which can guide the design of new target structures possessing high ethylene activity

    SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL ACTIVITY OF POLYMER NICKEL (II) COMPLEX

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    4-vinyl pyridine nickel complex containing polymerizable vinyl group, prepared by condensing (4:1 molar ratio) of 4-vinylpyridine with Nickel chloride, then polymerized with methyl methacrylate at 70 °C using AIBN as initiator. Metal complexand polymer metal complex have been characterized by elemental analyses, molar conductance, IR, 1H-NMR , Massspectra and thermal analyses (DTA and TGA). Conductivity measurement reveals the nonelectrolytic nature of thecomplex. This confirms that, the anion is coordinated to the metal ion. The IR reveal the metal ion is coordinated via thenitrogen atom of 4-VP. Nickel complex and polymer nickel complex have been tested invitro against number of tumor andnumber of microorganisms in order to assess their anti tumor and antimicrobial properties. The antimicrobial activity wasobserved by compounds VP-Ni and MMA-VP-Ni under the screening conditions. The activity against HCT-116 cells wasdetected for compound VP-Ni (with IC50 value 9.8±0.6 µg/ml), compared with reference standard (24.6±0.3 µg/ml) followedby MMA-VP-Ni (48.3±1.5). In conclusion, this study highlighted the synthesis of polymer nickel complex, and proved thepromising biological activity of the synthesized compounds

    Synthesis of high molecular weight polyethylene using FI catalyst

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    A FI Zr-based catalyst of bis[N-(3,5-dicumylsalicylidene)-2′,6′­diisopropylanilinato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature up to 35 oC were favorable for catalyst/MAO to raise the catalytic activity as well as the viscosity-average molecular weight (Mv) of polyethylene. The activity of the catalyst was linearly increased with increasing MAO concentration and no optimum activity was observed in the range studied. Although introduction of the bulky cumyl and 2′,6′-diisopropyl alkyl substitution groups on ortho positions to the phenoxy-oxygen and on phenyl ring on the N, respectively enhanced the viscosity average molecular weight (Mv) of the obtained polymer strongly, diminished the activity of the catalyst. Neither the activity of the catalyst nor the (Mv) of the obtained polymer were sensitive to hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst. The (Mv) of polyethylene ranged from 2.14×106 to 2.77×106 at the monomer pressure of 3 and 5 bar respectively which are much higher than that of the reported FI Zr-based catalysts

    UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization

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    Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15 prior polymerization. A study on polymerization activity of this catalyst has been performed under homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous particles and of the immobilization method is also carried out. Moreover, the thermal characterization, phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and final SBA-15 content have been established

    Structure and Cytotoxic Properties of Some Selected Gold(III) Complexes

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    We prepared four representative square planar gold(III) complexes - [AuCl3(Hpm)], [AuCl2(esal)], [AuCl(dien)]Cl2 and [Au(en)2]Cl3 -and characterized them both in the solid state and in solution. Thereafter, the cytotoxicity of these compounds was evaluated in vitro against the A2780 human ovarian tumor cell line that was used as the reference cell line. Remarkably, ali these gold(III) complexes showed significant cytotoxic effects, [AuCl2(esal)] showing a potency comparable to cisplatin. The present gold(III) complexes were also tested on the corresponding cisplatin-resistant line and revealed they were able to overcome resistance to cisplatin to a large extent. The implications of these findings for the development of new gold(III) complexes to be tested as antitumor agents are discussed
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