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Reversible addition-fragmentation chain transfer radical polymerization of styrene and maleic anhydride was successfully performed in continuous-flow microreactor. Results of the structural characterization showed that the obtained styrene-maleic anhydride (SMA) copolymers possessed controlled molecular weight, low dispersity and alternating structures. Subsequently, effects of the polymerization conditions, including reaction pressure, temperature, feed flowrate and tube length, on the polymerization kinetics and molecular structure of the SMA copolymers were investigated in detail. It was found that the reaction rate was increased as the reaction temperature increased within certain limits, as well as the feed flowrate due to the increased mass and heat transfer efficiency. Besides, first-order kinetics of the polymerization was observed when the reaction times were adjusted by only changing the tube length. Good stability was exhibited when the reaction conducted continuously for 10 h. This approach can reduce the reaction time significantly from several hours to about half an hour. [ABSTRACT FROM AUTHOR]

The new aminosilane compounds including Dimorpholindimethoxysilane (Donor-Pm), Di (1-methylpiperazine) dimethoxysilane (Donor-Pz) and Di (isopropylpiperazine) dimethoxysilane (Donor-Pi) were firstly synthesized and then employed as external donors for propylene polymerization with MgCl-supported Ziegler-Natta catalyst, compared with dipiperidine dimethoxysilane (Donor-Py). The effects of the aminosilane external donors on the catalytic activity, hydrogen response, and molecular weight distribution, crystalline ability, thermal property, isotactic sequence length, isotactic sequence distribution of polypropylene were studied by differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and self-nucleation and annealing (SSA), respectively. It was found that these new aminosilane compounds were conducive to improving the isotacticity of polypropylene and the catalytic activity. The GPC results showed that the molecular weight distribution of polypropylene prepared respectively by Donor-Pz or Donor-Pi with two N atoms on each amino substituent group was broader more than 8.0, especially for Donor-Pi with the large alkyl-substituted group on each nitrogen atom, the molecular weight distribution of polypropylene was about 11.2, which was much broader than that of industrial polypropylene about 4 ~ 5. The DSC results indicated that the degrees of crystallinity of polypropylene prepared by the aminosilane external donors were higher, and the crystallization ability of polypropylene prepared by Donor-Pi was lower but closed to that of polypropylene prepared by Donor-Py. The SSA results indicated Donor-Py and Donor-Pi were conducive to improving the relative contents of the highest isotactic component of polypropylene, and the lamellae thicknesses results showed the sequence length of polypropylene prepared by Donor-Py and Donor-Pi were longer, and the isotactic sequence distribution of polypropylene prepared by Donor-Py and Donor-Pi were broader. The study results showed that the new aminosilane donor Donor-Pi was conducive to improving the stereo-regularity of polypropylene, especially revealing that it was a simple and an effective method to synthesize broad molecular weight distribution of polypropylene by using appropriate aminosilane external donor for propylene polymerization. [ABSTRACT FROM AUTHOR]

Four novel well-defined polyethylene-bound antioxidants (PE-bound antioxidants) with distinct secondary structures are synthesized via transesterification reactions between methyl 3-(3,5-di- tert-butyl-4-hydroxyphenyl)propionate and hydroxyl-terminated polyethylenes. The results of thermal gravimetric analysis under an air atmosphere demonstrate that the thermal stabilities of PE-bound antioxidants are higher than that of commercial antioxidant Irganox1076 and are strongly related to their chemical structures. Particularly, the most thermally stable PE-bound antioxidant is the one bearing both primary and secondary antioxidant moieties. The antioxidant activities of the PE-bound antioxidants are evaluated in polypropylene by their melt flow index. [ABSTRACT FROM AUTHOR]

MgCl2/TiCl4/diether is a fifth-generation Ziegler-Natta catalyst for the commercial polymerization of propylene. The outstanding features of this catalyst are the high activity and high isotacticity for propylene polymerization without using an external electron donor. In this study, we explored the copolymerization of propylene and 1-octene with MgCl2/TiCl4/diether catalyst. It was found that MgCl2/TiCl4/diether catalyst showed higher polymerization activity and led to greater 1-octene content incorporation, compared with a fourth-generation Ziegler-Natta catalyst (MgCl2/TiCl4/diester). With an increase in 1-octene incorporation in polypropylene chains, the melting temperature, glass transition temperature and crystallinity of the copolymers decreased distinctly. The microstructures of the copolymers were characterized using 13C NMR spectroscopy, and the copolymer compositions and number-average sequence lengths were calculated from the dyad concentration and distribution. This result is very important for the in-reactor polyolefin alloying process, especially for the case of a single catalyst and two-step (or two-reactor) process. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

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.

Details the development of a catalytic system with high polymeric activity. Intercalation of the cocatalysts, which included methylaluminoxane (MAO, between layers of montmorillonite (MMT) for ethylene oligomerization; Formation of a dual functional catalytic system by adding metallocene catalyst Me2Si(Ind)2ZrCl2 and MAO; Preparation of the PE/MMT nanocomposite by copolymerization of ethylene with α-olefins produced in situ from ethylene; Conclusion that the PE/MMT nanocomposites are stable and have more tensile strength; Temperature of maximum weight loss (Tonset).

Investigates the polymerization method in the preparation of long-branched polyethylene (LBPE). Use of late transition metal and metallocene catalysts; Characteristics of LBPE; Determination of narrow molecular weight distribution.

Examines the polymerization of a linear low-density polyethylene. Observation of high activity in the catalytic system; Determination of the melting point of the polymer; Production of narrow molecular weight distribution.

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]

Fivenew alkoxysilanes with different sizes of hydrocarbon substituentswere first synthesized and employed as external donors for propylenepolymerization with a Ziegler–Natta catalyst. The effects ofthese and industrial alkoxysilanes with different sizes of hydrocarbonsubstituents on the microstructure of polypropylene were studied bySSA and 13C NMR. The results showed that isotactic sequencelength of polypropylene increased with the size of R2substituenton alkoxysilanes in the five donor systems, similar to the regularityof molecular weight, isotacticity, and thermal properties of polypropylene.Although the polypropylene produced by double cycloalkane substituentson alkoxysilanes had lower lamellae thickness L1, its contents were the highest. Moreover, excess large volumeof hydrocarbon substituents on alkoxysilanes might be detrimentalto improving isotactic sequence length of polypropylene. Polypropyleneprepared by MIPDMS had a more uniform distribution of the stereodefects,indicating that MIPDMS might be used for the industrial productionof BOPP. [ABSTRACT FROM AUTHOR]

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]

A series of aryl-substituted tetramethylcyclopentadienyl zirconocenes (C5Me4C6H4X-4)Cp′MCl2 [Cp′=C5H5, X=H (5), Me (6), Cl (7) or OMe (8); Cp′=Ind, X=H (9), Me (10) or Cl (11); Cp′=2-Ph-Ind, X=H (12)] and (C5Me4C6H4X-4)2ZrCl2 [X=H (13), Me (14), Cl (15)], with different substituents at the 4-position of phenyl, have been prepared by the reaction of the corresponding ligands (C5Me4HC6H4X-4) [X=H (1), Me (2), Cl (3) or OMe (4)] with n-BuLi, ZrCl4 and Cp′Li or with n-BuLi and ZrCl4. Ethylene polymerization with these complexes in combination with MAO has been studied. The electron donor (Me) at the 4-position of phenyl led to an increase in catalytic activity while the electron-withdrawing group (Cl) and the strong π donor (OMe) led to its decrease. Complexes 5, 6, 9 and 10 exhibited very high activities, but 13–15 showed much lower activities due to the bulky steric effect. The molecular structure of 5 has been determined by X-ray diffraction. The relationship between structures of catalysts and catalytic activities were discussed. [Copyright &y& Elsevier]