Weiguang Shi

Antioxidant capacity and kinetics of dendritic hindered phenols using DPPH assay

Dendritic hindered phenols were synthesised using 3-(3,5-di-tert-butyl-4-hydroxy-phenyl)-propionic acid and dendritic poly(amido-amine) (PAMAM) as materials. The structures of the dendritic hindered phenols were characterised by infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance spectroscopy (1H NMR) and liquid chromatography–mass spectrometry (LC-MS). The scavenging capacity and kinetics of the dendritic hindered phenols were investigated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. These dendritic hindered phenols have excellent scavenging capacity, being superior to antioxidants 1010 and 1098 with the same number of phenol hydroxyl groups. The scavenging capacity of the first-generation dendritic hindered phenol (1.0G dendritic phenol) was superior to that of the second-generation dendritic hindered phenol (2.0G dendritic phenol). The kinetic behaviour of the hindered phenols in scavenging the DPPH radical was a first-order reaction. The scavenging rate constants (k1) of the dendritic phenols with DPPH radical were higher than that of antioxidants 1010 and 1098, while the k1 value of 1.0 G dendritic phenol was superior to that of 2.0 G dendritic phenol under the same test conditions. The scavenging activation energy (Ea) of 1.0 dendritic phenol with four phenolic groups and two tertiary amine groups was the lowest, while that of antioxidant 1010 with a higher molecular weight and four phenolic groups was the greatest.

Novel dendrimer-based nickel catalyst: synthesis, characterization and performance in ethylene oligomerization

A novel nickel metallodendrimer was synthesized with poly(amidoamine), 3,5-di-tert-butyl-2-hydroxy-benzaldehyde and nickel chloride via the Schiff’s base and the complexation reactions. Structures of the dendritic ligand and its nickel complex were characterized by IR, NMR, UV, ESI-MS and elemental analyses. This new nickel metallodendrimer as a catalyst precursor, together with methylaluminoxane as an activator, was evaluated in the ethylene oligomerization. Under the conditions of 0.5 h, 0.5 MPa, 25°C and Al/Ni mole ratio 500: 1 employed for the nickel complex, the catalytic activity showed a maximum value of 4.93 × 105 grams per mole of Ni catalyst per hour. Substituents on the benzene ring seem to have a negative influence on the catalytic activity of the complex.

Cobalt complexes based on dendritic PAMAM bridged salicylaldimine ligands: Synthesis, characterization and performance in ethylene oligomerization

ABSTRACT Two novel dendritic poly(amido-amine) (PAMAM) bridged salicylaldimine ligands were synthesized by Schiff base reaction using 1.0 generation dendritic PAMAM as bridged groups. The cobalt complex with 1,4-butanediamine as core (C1) and the cobalt complex with 1,6-hexanediamine as core (C2) based on dendritic PAMAM bridged salicylaldimine ligands were prepared by metallic coordination reaction, respectively. The structures of the ligands and the dendritic cobalt complexes were characterized by fourier transform infrared (FTIR), ultraviolet spectra (UV), hydrogen nuclear magnetic resonance (1H NMR) and electrospray ionization mass spectra (ESI-MS). The complexes C1 and C2 were evaluated as catalyst precursors for ethylene oligomerization after being activated with methylaluminoxane (MAO), diethylaluminum chloride (Et2AlCl), ethylaluminium dichloride (EtAlCl2) and ethylaluminum sesquichloride (EASC). The dendritic cobalt complexes exhibited the highest activity and selectivity for high carbon oligomers with EASC as activator. Under the conditions of 1.0 MPa, 25°C and Al/Co molar ratio 1500, the catalytic activity and selectivity for C10–C20 using C1 were 3.44×106 g·(mol Co·h)−1 and 76.53% after activation with EASC, and the catalytic activity and selectivity for C10–C20 using C2 were 3.42×106 g·(mol Co·h)−1 and 84.50%, respectively.

Hyperbranched bisphosphinoamine ligands: synthesis, characterization and application in ethylene oligomerization

Abstract Two hyperbranched bisphosphinoamine (PNP) ligands and chromium complexes were synthesized in good yield with 1.0 generation (1.0 G) hyperbranched macromolecules, chlorodiphenylphosphine (Ph2PCl) and CrCl3(THF)3 as raw materials. The hyperbranched PNP ligands and chromium complexes were characterized by FT-IR, 1H NMR, 31P NMR, UV and ESI-MS. Comparing with the chromium complexes, the hyperbranched PNP ligands, in combination with Cr(III), and activation by methylaluminoxane (MAO) in situ generated species with better catalytic performance for ethylene oligomerization. The effect of solvent, chromium source, ligand/Cr molar ratio, reaction temperature, Al/Cr molar ratio and reaction pressure on the catalytic activity and product selectivity were studied. The results showed that with increase of ligand/Cr molar ratio, reaction temperature and Al/Cr molar ratio, the catalytic activity increased at first and then decreased. However, the catalytic activity continuously increased with increase of reaction pressure. Under the optimized conditions, the catalytic system of hyperbranched PNP/Cr(III)/MAO led to catalytic activity of 2.68 × 105 g/(mol Cr·h) and 37.71% selectivity for C6 and C8.

Interface Activity and Thermodynamic Properties of Cardanol Polyoxyethylene Ether Carboxylates

Abstract A series of saturated cardanol polyoxyethylene ether carboxylates was synthesized using renewable saturated cardanol originating from Cashew Nut Shell Liquid as raw material. The structures were characterized by hydrogen nuclear magnetic resonance spectroscopy. The studies of their surface activity and interface activity were carried out to analyze the influence of the chemical structures of the series of cardanol surfactants on the adsorption and micellization. Results showed that saturated cardanol polyoxyethylene ether carboxylates had a good surface activity and interface activity, and the interface activities of the Gemini cardanol surfactants were better than those of the corresponding monomer cardanol surfactants. The critical micelle concentrations (CMC) of all investigated cardanol surfactants, obtained from surface tension measurements, were low in the order of 10−5 mol/L. The CMCs decreased and the oil-water interface tension for the same cardanol surfactants increased with the increase of the oxyethylene number. The process of micellization became easier with increasing the oxyethylene number. The ΔGθm values of the Gemini cardanol surfactants were more negative than those of the corresponding monomer cardanol surfactants. The micellization for all cardanol surfactants was a spontaneous process and exhibited enthalpy-entropy compensation. The micellization of all the cardanol surfactants was entropy-driven.

Kinetics and structure-activity relationship of dendritic bridged hindered phenol antioxidants to protect styrene against free radical induced peroxidation

A series of dendritic poly(amido-amine) (PAMAM) bridged hindered phenols antioxidants were synthesized. The active antioxidant group (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) was attached to two generations of PAMAM dendrimers, and their structure was verified by nuclear magnetic resonance (NMR) and fourier transform infrared spectra (FT-IR). The antioxidant abilities of the dendritic phenols to inhibit the oxidation of styrene were evaluated and the relationships between the length of core, the generation of dendrimers and the antioxidant activities were established. The reaction kinetics of scavenging peroxyl radicals was followed by oxygen consumption. The inhibition time (tinh) values showed the dendritic phenols had the ability of scavenging peroxyl radicals, and that the antioxidant ability increased with the increasing length of the core and the generation. The kinetic analysis demonstrated that dendritic phenols could slow the rate of styrene peroxidation induced by AIBN, as shown by the number of trapping ROO· (n), and this role was in accordance with that of the tinh values.

Synthesis of short straight-chain alkylamine based hyperbranched nickel complexes and their catalytic performance of ethylene oligomerization

ABSTRACT Short straight-chain alkylamine based hyperbranched molecules and their corresponding salicylaldimine nickel complexes have been synthesized in high yield and characterized by FTIR, 1H-NMR and mass spectrometry. The optimal reaction parameters were determined under the catalytic system of methylaluminoxane (MAO) as co-catalyst and toluene as solvent. Under these conditions, the effect of catalyst structure, solvent and co-catalyst were determined. Upon activation of MAO in toluene, ethylene oligomerization products were homogeneous distribution of butene, hexene and octene with trace higher olefin. The same catalytic system under cyclohexane and methyl cyclohexane as solvent, however, produced majority of butene. Under the activation of EtAlCl2, Et2AlCl and EASC as co-catalyst in toluene, ethylene oligomerization reaction was tandem with Friedel-Crafts reaction in catalytic system.