Polymerization of methyl methacrylate using bis(imine)cobalt, a polyolefin catalyst

A mono-nuclear catalyst of bis-imine cobalt (MC) was synthesized with using 2,6-dibenzhydryl-4-ethoxy phenyl as a ligand. The so huge ligand was prepared via the reaction of 2,6-dibenzhydryl-4-ethoxy phenyl)-N=(CH3)-C(CH3)=O with diacetyl with equal mole stoichiometry in presence of formic acid catalysis. The catalyst was synthesized via a reaction between the ligands and cobalt salt (CoCl2). The catalyst was used for polymerization of methyl methacrylate (MMA), (a polar monomer) in the presence of modified methylaluminoxane (MMAO). The highest polymerization activity (8.6 g PMMA/mmol cat. h) was obtained at [cocatalyst]/[catalyst]=1000:1 molar ratio and at room temperature reaction. For the prepared PMMA, Polymer with branching density of 263/1000C was obtained using 1H NMR technique calculation. The microstructure of one of the produced PMMA was as follow: 48% syndiotactic, 29% isotactic and 23% atactic. GPC analysis of the polymer showed a number average molecular weight of about 5.7 × 105 g/mol and a narrow molecular weight distribution of 1.57

Homo- and co-polymerization of polar and non-polar olefinic monomers using bicenter cobalt-diimine catalysts

Bicenter (BCn) cobalt-bis(imine) catalysts were synthesized, used to polymerize methyl methacrylate (MMA), and 1-hexene. The effect of catalyst structure, bridging ligand, and polymerization reaction conditions were investigated. Synthesis of primary ligand of (2,6-dibenzhydryl-4-ethoxyphenyl)-N=(CH3)-C(CH3)=O is prepared. Following to that, the final ligands of BC1 and BC2 bicenter catalysts were prepared via reacting the primary ligand with 2,3,5,6-tetramethylbenzene-1,4-diamine and 4,4-methylenedianiline bridges, respectively. The BC1 catalyst demonstrated higher activity than the BC2 catalyst. The highest activity for the BC1 catalyst was obtained when the co-catalyst to catalyst molar ratio was [Al]/[Co]=1500:1, and the polymerization temperature was 40 °C. In comparison the BC2 catalyst demonstrated the highest activity in [Al]/[Co]=500:1 ratio, polymerization temperature of 70 °Cand showed higher thermal stability. 1HNMR analysis revealed that the highest branching density for poly(methyl methacrylates) (PMMA) produced by BC1 and BC2 catalysts was 222 and 249 branches per 1000 carbon atoms, respectively. PMMA synthesized with BC2 catalysts had the highest syndiotacticity (59%). The polymer produced with bicenter catalyst (BC1) had a relatively broad molecular weight distribution (2.9), according to GPC analysis. The synthesized catalysts demonstrated appropriate activity for the polymerization of MMA, but only moderate activity for 1-hexene monome

Determination of gel content of silane cross-linked polyethylene copolymers using FTIR technique

Silane cross-linking of metallocene-based polyethylene-octene elastomer (POE)/linear low density polyethylene (LLDPE) blend was carried out using two-step Sioplas process in an industrial scale twin-screw extruder. In the study, grafting and cross-linking reactions of vinyl trimethoxy silane (VTMS) were analyzed using FTIR technique. It was found that the cured compound showed absorption peaks at 1078 cm-1 and 955 cm-1 related to Si-O-Si bonds. A peak was also observed at 3405 cm-1 of hydroxyl group produced from hydrolysis of methoxyethylene group during of curing process, reflecting that curing reaction was not completed. The samples were cured at different time intervals (15 min-16 hours). The gel content values determined by solvent extraction and FTIR were in good agreement at curing times more than 4 hours. The efficiency of the silane grafting reaction was determined using the ratio of the absorption peak at 1092 cm-1 characteristic of methoxy to the transmittance peak at 1378 cm-1 characteristic of methyl group, which  is considered as the internal standard. The results showed the highest efficiency of silane grafting reaction at 5 w% of VTMS with the least amount of internal standard ratio (0.029), at which the lowest MFI value, and the highest values for gel content, tear strength, compression set and hot set 200 °C were obtained

Effect of Polysulfone and Graphene Nanosheets on the Flexibility of Epoxy Coatings

Epoxy resin has remarkable properties including excellent mechanical and electrical properties, thermal and chemical stability, and resistance to creep. On the other side, these resins are brittle with low resistance toward crack initiation and its growth. In order to solve this problem, thermoplastic polysulfone and graphene nanosheets have been used as filler for improving the flexibility of epoxy coatings. The effect of adding different amounts (1, 0.5, 2.5, 5 wt%) of polysulfone and 0.5 wt% of graphene nanosheets on the epoxy properties was investigated by thermal analysis (DSC), tensile strength, impact resistance and determining the gel content of samples. The results showed that the tensile strength of epoxy resin increased by adding polysulfone, and the graphene nanosheets could improve flexibility of the sample containing 1 wt% polysulfone. The study of thermal properties of cured samples by means of DSC analysis showed that the addition of polysulfone into the epoxy network resulted in changing the glass transition (Tg) of the resin. With incorporation of graphene nanosheets into the polymer matrix, the modulus decreased due to the reduction in number of crosslinks. The study in impact resistance of the samples showed that those containing 1 wt% polysulfone and 0.5 wt% graphene displayed high strength and impact resistance. These types of compounds can be used in flexible and anticorrosion coatings

A new nanostructured material amino functionalized mesoporous silica synthesized via co-condensation method for Pb(II) and Ni(II) ion sorption from aqueous solution

In this investigation, MCM-41/N-(3-trimethoxysilyl)-propyl)diethylenetriamine (MCM-41/TMSPDETA) adsorbent was prepared via co-condensation method and characterized by FTIR, BET, XRD, TEM, SEM and DLS analytical techniques. Experiments were carried out to investigate the influence of different sorption parameters, such as pH, adsorbent dosage, contact time, initial concentration of heavy metal ions and solution temperature in a batch system. Optimum conditions of sorption experiments were obtained at 20 degrees C with the pH of 6.0 and contact time of 60 min for Pb(II) and 120 min for Ni(II). The pseudo-first-order, the pseudo-second-order and intraparticle diffusion models have been used to analyze the sorption kinetic results. The sorption process was found to be well described by the pseudo-second-order rate model. The Langmuir and Freundlich isotherms have been used to describe the equilibrium sorption; the adsorption data obeyed the Langmuir isotherm. The maximum capacity of the nanosorbent was 77.52 and 58.47 mg g(-1) for Pb (II) and Ni (II) ions, respectively. In order to verify the nature of sorption processes as physical or chemical, the equilibrium data were also fitted to the Dubinin-Radushkevitch (D-R) model. Based on D-R isotherm results, the values of mean free energy were 13.36 and 9.13 kJ mol(-1) for Pb(II) and Ni(II) sorption, respectively. These values of E (kJ mol-1) indicating chemical sorption for both metal ions. The selectivity order of lead and nickel sorption onto the adsorbent was Pb(II) > Ni(II). (C) 2016 Elsevier B.V. All rights reserved

Polar tagging in the synthesis of monodisperse oligo(p-pheny leneethynylene)s and an update on the synthesis of oligoPPEs

Sahoo D, Thiele S, Schulte M, Ramezanian N, Godt A. Polar tagging in the synthesis of monodisperse oligo(p-pheny leneethynylene)s and an update on the synthesis of oligoPPEs. BEILSTEIN JOURNAL OF ORGANIC CHEMISTRY. 2010;6:57.One important access to monodisperse (functionalized) oligoPPEs is based on the orthogonality of the alkyne protecting groups tri-isopropylsilyl and hydroxymethyl (HOM) and on the polar tagging with the hydroxymethyl moiety for an easy chromatographic separation of the products. This paper provides an update of this synthetic route. For the deprotection of HOM protected alkynes, gamma-MnO2 proved to be better than (highly) activated MnO2. The use of HOM as an alkyne protecting group is accompanied by carbometalation as a side reaction in the alkynyl-aryl coupling. The extent of carbometalation can be distinctly reduced through substitution of HOM for 1-hydroxyethyl. The strategy of polar tagging is extended by embedding ether linkages within the solubilising side chains. With building blocks such as 1,4-diiodo-2,5-bis(6-methoxyhexyl) less steps are needed to assemble oligoPPEs with functional end groups and the isolation of pure compounds becomes simple. For the preparation of 1,4-dialkyl-2,5-diiodobenzene a better procedure is presented together with the finding that 1,4-dialkyl-2,3-diiodobenzene, a constitutional isomer of 1,4-dialkyl-2,5-diiodobenzene, is one of the byproducts

Combined effects of polyacrylamide and nanomagnetite amendment on soil and water quality, Khorasan Razavi, Iran

Nanotechnology is increasingly being used to remediate polluted soil and water. However, few studies are available assessing the potential of nanoparticles to bind surface particles, decrease erosion, and minimize the loading of water pollutants from agricultural surface discharge. To investigate this potential, we treated in situ field plots with two practical surface application levels of anionic polyacrylamide (PAM only) with and without nanomagnetite (PAM-NM), examined soil physical properties, and evaluated the impact of this amendment on contaminant sorption and soil erosion control. Polyacrylamide and PAM-NM treatments resulted in 32.2 and 151.9 fold reductions in Mn2+, 1.8 and 2.7 fold for PO43--P, and 2.3 and 1.6 fold for NH4+-N, respectively, compared to the control. Thus, we found that the combination of PAM and NM, had an important inhibitory effect on NH4+-N and PO43--P transport from soil-pollutants which can contribute substantially to the eutrophication of surface water bodies. Additionally, since the treatment, especially at a high concentration of NM, was effective at reducing Mn2+ concentrations in the runoff water, the combination of PAM and NM may be important for mitigating potential risks associated with Mn2+ toxicity. Average sediment contents in the runoff monitored during the rainfall simulation were reduced by 3.6 and 4.2 fold for the low and high concentration PAM-NM treatments when compared to a control. This treatment was only slightly less effective than the PAM-only applications (4.9 and 5.9 fold, respectively). We report similar findings for turbidity of the runoff (2.6-3.3 fold for PAM only and 1.8-2.3 fold for PAM-NM) which was caused by the effects of both PAM and NM on the binding of surface particles corresponding to an increase in aggregate size and stability. Findings from this field-based study show that PAM-modified NM adsorbents can be used to both inhibit erosion and control contaminant transport

Surface functionalized mesoporous silica nanoparticles as an effective carrier for epirubicin delivery to cancer cells

Recent studies with inorganic nanoparticles modified with functional groups have demonstrated improvement in drug delivery into cancer cells. In the present study, we prepared, characterized, and evaluated mesoporous silica nanoparticles (MSNs) as carriers for epirubicin hydrochloride (EPI) in order to improve the antitumor efficacy of this drug. MSNs were prepared and functionalized with phosphonate, polyethylene glycol (PEG) and polyethylenimine–polyethylene glycol (PEI–PEG) groups. Different nanoparticulate formulations were loaded with EPI. The in vitro cytotoxicity and the in vivo antitumor efficacy of MSNs containing EPI were evaluated versus free EPI. The EPI release from nanoparticles was shown to be pH-dependent. The size of MSNs functionalized with polyethyleneimine-polyethylene glycol (MSN–PEI–PEG) was 123.8 ± 4.8 nm. This formulation showed the best antitumor effects at an EPI dose of 9 mg/kg in C-26 colon carcinoma model. The biodistribution results proved that MSN–PEI–PEG–EPI had a higher tumor accumulation compared to free EPI, 3 h after drug administration. The results indicated that this formulation could be effective nanocarriers for anti-tumor therapies

Linear and Kinked Oligo(phenyleneethynylene)s as Ideal Molecular Calibrants for Forster Resonance Energy Transfer.

Czar MF, Breitgoff FD, Sahoo D, et al. Linear and Kinked Oligo(phenyleneethynylene)s as Ideal Molecular Calibrants for Forster Resonance Energy Transfer. The journal of physical chemistry letters. 2019;10(21):6942-6947.We show that oligo(phenyleneethynylene)s (oligoPEs) are ideal spacers for calibrating dye pairs used for Forster resonance energy transfer (FRET). Ensemble FRET measurements on linear and kinked diads with such spacers show the expected distance and orientation dependence of FRET. Measured FRET efficiencies match excellently with those predicted using a harmonic segmented chain model, which was validated by end-to-end distance distributions obtained from pulsed electron paramagnetic resonance measurements on spin-labeled oligoPEs with comparable label distances