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Abstract: Melamine (MA) was polymeric modified by condensation reacting with formaldehyde (FA) to form the melamine formaldehyde polycondensate (abbreviation: MF) with high molecule-weight and comparatively high processing thermo-stability. The effect of the reacting molar ratio of MA and FA, and the types and concentrations of the dispersion agents on the structure and properties of MF were discussed, and the finely divided, cross-linked, and thermo-stable MF polycondensates were obtained. The thermal stabilization effect of MF on POM was studied by the isothermal weight loss analysis at 220°C, isothermal weight loss rate analysis at 222°C, thermal gravity analysis (TGA) and balance torque analysis, which showed that MF has almost the equal thermal stabilization on POM to MA. The multiple processing and long-term thermal stability at high temperature measurements indicated that MF showed even higher thermal stabilization on POM than MA. Moreover, the impact strength was improved after five times of extrusion, due to the better dispersion of MF in POM matrix and better nucleation effect of MF on POM. [Copyright &y& Elsevier]

Abstract: The functionalization of polyolefins has long been an industrially important yet scientifically challenging research subject ever since the commercialization of polyethylene (PE) and polypropylene (PP) in the 1950s. However, only until recently has considerable progress been made thanks to the enormous development of transition metal olefin polymerization catalysis (Ziegler-Natta, metallocene and post-metallocene). This review covers recent achievements in the functionalization of polyolefins, with special attention being paid to the chemistries using transition metal-catalyzed process to synthesize structurally well-defined functional polyolefins, including side group-functionalized polyolefins, chain end-functionalized polyolefins and functional polyolefins with graft and block structures. [Copyright &y& Elsevier]

Discusses the synthesis of well-defined functional polyethylene graft copolymer via atom transfer radical polymerization (ATRP) process. Transformation of the pendant styrene groups into ATRP initiator sites; Determination of the quantitative hydrochlorination reaction; Lack of polar functional groups on its polymer chain.

A series of vanadium catalysts with bulky bis(N-heterocyclic carbenes) (bis-NHCs) ligands were synthesized by in-situ reaction. With diethylaluminum chloride (AlEt 2 Cl) as cocatalyst and ethyl trichloroacetate (ETA) as activator, these catalysts exhibit good activity when used to catalyze ethylene (co)polymerization. The structure of the catalyst, especially the bridging carbons number of the bis-NHCs ligands, is related to the performance of the (co)polymer. When the bis-NHCs ligand with t Bu substituted, increased the bridging carbons number of the bis-NHCs ligand is easier to obtain higher molecular weight polymers. But when the bis-NHCs ligand with 2,6-diisopropyl phenyl substituted, the increase of the bridging carbons number is not conducive to obtaining higher molecular weight polymers. Under the same concentration of comonomer, the increase of the bis-NHCs ligand bridged carbon number of the V-complexes is more beneficial to obtain the copolymer with high norbornene (NB) content. [Display omitted] • The first application of bis-NHCs ligands in vanadium (III) catalyzed olefin polymerization. • The bis-NHCs vanadium (III) complex were obtained by in-situ reaction for the first time. • Relationships were found to exist between the bis-NHCs ligand structure of the catalyst and the catalytic performance. [ABSTRACT FROM AUTHOR]

Abstract: A novel zirconium complex bearing bis(phenoxyketimine) ligand (1) bis((3,5-di-tert-butyl-C6H2-2-O)PhC N(2,4-di-fluoro-C6H3))ZrCl2 (2) was prepared and successfully immobilized on a mesoporous molecular sieve MCM-41 in chemical method. Results of slurry polymerization of ethylene with MCM-41-supported catalyst (MC) indicated that the morphologies of polyethylene obtained differed greatly in heptane and toluene. Homogeneous catalyst 2 exhibited a very high initial activity in ethylene polymerization at room temperature resulting in great viscosity of the system. When immobilized on MCM-41, MC showed a smooth yet highly active kinetic behavior. With MAO as the cocatalyst, the effects of Al/Zr molar ratio and polymerization temperature on catalytic activity and properties of polyethylene obtained were investigated. The results showed that polyethylene obtained with MC possessed higher molecular weight (M n) and broader molecular weight distribution (M w/M n) than those formed with its homogeneous counterpart. [Copyright &y& Elsevier]

Isotactic polypropylene (iPP) with narrow molecular mass distribution was freeze-extracted from n-octane solutions with varying concentrations. The recovered samples were characterized by differential scanning calorimetry. It is found that the sample recovered from the very dilute solution exhibits the higher non-isothermal crystallization temperature, faster isothermal crystallization rate, and smaller Avrami index. And there should exist a critical concentration corresponding with the critical overlap concentration proposed by de Gennes in the polymer solutions. In the solution well below the critical concentration, the iPP chains were isolated from each other, resulting in an acceleration of melt crystallization for the recovered samples. It seems that the chain entanglement is a barrier to the melt crystallization of polymer. [Copyright &y& Elsevier]

Chlorinated polypropylene(CPP), chlorinated polyethylene(CPE) and chlorinated polyvinyl chloride(CPVC) with high chlorine content were carbonized in inert and air atmosphere. After carbonization condition optimized, porous carbon with a surface area of 1035 m2/g is prepared in mild carbonization condition and without any activation. Chlorinated polypropylene(CPP), chlorinated polyethylene(CPE) and chlorinated polyvinyl chloride(CPVC) with high chlorine content were used to prepare porous carbons under inert gas and air atmosphere, respectively. Due to their flame retardance, carbon materials were both prepared from two atmosphere through thermal dehydrochlorination. The microstructure and porous textures of the obtained carbons were characterized by BET, XPS, SEM, TEM, XRD and Raman, respectively. The results show that the dehydrochlorination of all precursors is more efficient in air than nitrogen, because the oxygen molecular in air atmosphere accelerates the elimination of hydrogen chloride(HCl). Moreover, CPP-derived carbons display apparent higher surface area than that derived from CPE and CPVC. Furthermore, the carbonization condition is optimized and porous carbon with a surface area of 1035 m2/g is prepared in mild carbonization condition and without any activation. [ABSTRACT FROM AUTHOR]