Search

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: An effective route to synthesize the amphiphilic diblock copolymer containing a poly(ε-caprolactone) block and a polyolefin block, such as polyethylene, syndiotactic polystyrene and isotactic polypropylene is discussed in this article. There are two reaction steps including the preparation of polyolefins by the combination of metallocene/methylaluminoxane as catalyst system and various chain transfer agents as well as the subsequent anionic ring-opening polymerization of ε-caprolactone. The molecular structure in terms of composition, molecular weight, molecular weight distribution of the diblock copolymers prepared is controllable by these well-defined reaction mechanisms. The scanning electron microscope (SEM) results showes that the compatibilities of the polyolefins and polycarbonate blends are improved greatly using these amphiphilic diblock copolymers as the polymeric compatilizers. [Copyright &y& Elsevier]

Abstract: PP-g-PS copolymers were synthesized with the same polypropylene (PP) backbones and various side chain lengths of PS sequences via reactive comonomer p-allyltoluene (p-AT) by Ziegler–Natta copolymerization and the subsequent living anionic graft-polymerization. 1H NMR characterized that the PP-g-PS copolymer had grafted 3.15 side chains per 1000 carbons in the PP backbones and the length of PS sequences varied in the range of 25.8–309.9 units. PP/PS blends with the PP-g-PS copolymer as compatibilizer (wt. 75/25/5) were prepared and characterized by SEM, WAXD and DMA to investigate the morphologies, crystallinity and glass transition temperatures of the PP/PS blends. All the results pointed out that the average side chain length (GL) of the graft copolymer (GL is from 25.8 to 309.9) made great effects of the PP/PS blends, such as the PS dispersed phase, the crystallinity of the PP component and the two glass transition temperatures of the blends, which showed the same trend with the increase of the GL. Overall, only with a suitable average side chain length, the PP-g-PS copolymer could achieve optimal compatibilizing efficiency of the PP/PS blends. [Copyright &y& Elsevier]

Abstract: The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler–Natta catalyst supported on MgCl2. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP-co-ADMS was chlorinated to PP–Si–Cl by refluxing the copolymer with SOCl2 in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst to produce graft copolymer PP-g-PMMA, which was characterized with 1H NMR, 13C NMR, GPC and DSC. Polymer blend of iPP/PP-g-PMMA/PMMA was prepared and the results shown that PP-g-PMMA was an effective compatilizer. [Copyright &y& Elsevier]

Abstract: A novel layered calcosilicate (CAS-1) was employed to immobilize an iron-based diimine catalyst 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine iron chloride (I) onto it to form a supported catalyst (CC) for the first time. The crystal structure of CAS-1 was determined by X-ray crystallographic analysis in addition to SEM characterization. The CC-catalyzed ethylene polymerization exhibited good catalytic activities with either co-catalyst methylaluminoxane (MAO) or triethylaluminum (TEA). The resulting polyethylenes possessed not only higher molecular weight, melting temperature (T m), and decomposition onset temperature (T onset) than those obtained with its homogeneous counterpart, but also a unique morphology. [Copyright &y& Elsevier]

Abstract: Methyl methacrylate (MMA) and styrene (St) have been radically polymerized in the presence of chlorotrimethylsilane and CuCl/N,N,N′,N″,N″-pentamethyldiethyltriamine (Me3SiCl/CuCl/PMDETA). An analysis of the resultant polymers by 1H NMR discloses terminal silyl group and chlorine atom in all the obtained polymers. Kinetics studies have been carried out by measuring monomer conversions and polymer molecular weights against polymerization time. The results indicate that, for both MMA and St polymerizations, the monomer conversions exhibit a quasi-linear relationship with polymerization time, and the polymer number-average molecular weight (M n) also increases with monomer conversion. The molecular weights of both PS and PMMA exceed one hundred thousand. Regardless of molecular weight, all the polymers show narrow molecular distributions (M w/M n =1.2–1.5). These polymerization reactions are speculated to follow a mechanism similar to that of atom transfer radical polymerization (ATRP). [Copyright &y& Elsevier]

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]

Abstract: An interference-free tandem catalysis based on iron catalyst and TiCl4/MgCl2, activated by MAO, was used to prepare branched polyethylene by polymerization of ethylene. No obvious deactivation due to the side reaction of catalysts and cocatalysts was detected during the reaction process, which commonly existed in tandem catalytic systems based on conventional Ziegler–Natta catalysts. A series of branched polyethylene with different properties have been prepared by adjusting of reaction temperature, Fe/Ti molar ratio and the amount of MAO used. The alteration of oligomers concentration in the reaction system, by changing of reaction conditions, led to the products with different branching degrees, thus the thermal properties and molecular weight. The products obtained in toluene at lower Fe/Ti ratios exhibited better morphology than those obtained at higher Fe/Ti ratios. [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]