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1.
    
A model for olefin–diene copolymerization and long chain branch formation was developed. The model shows that the number‐average molecular weight and branching density increases linearly with time in a semi‐batch polymerization, while the polydispersity depends on the diene content in the polymer and on the polymerization time. For low diene fractions or low polymerization times, the polydispersity increases linearly with time. For higher diene contents, the polydispersity increases exponentially with polymerization time after a critical polymer concentration is reached. The calculated distributions of branched species indicate that diene content influences the amount of highly branched chains produced in the polymerization, markedly broadening the distribution of molecular weight and leading to gel formation.

Weight distribution of branched species after 30 min of polymerization.  相似文献   


2.
    
A series of heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐tBu‐2‐OC6H3CH?N(C6F5)] [PhN?C(CF3)CHCRO]TiCl2 [ 3a : R = Ph, 3b : R = C6H4Cl(p), 3c : R = C6H4OMe(p), 3d : R = C6H4Me(p), 3e : R = C6H4Me(o)] were synthesized and characterized. Molecular structures of 3b and 3c were further confirmed by X‐ray crystallographic analyses. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts displayed favorable ability to incorporate 5‐vinyl‐2‐norbornene (VNB) and 5‐ethylidene‐2‐norbornene (ENB) into the polymer chains, affording high‐molecular weight copolymers with high‐comonomer incorporations and alternating sequence under the mild conditions. The comonomer concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resultant copolymer. At initial comonomer concentration of higher than 0.4 mol/L, the titanium complexes with electron‐donating groups in the β‐enaminoketonato moiety mediated room‐temperature living ethylene/VNB or ENB copolymerizations. Polymerization results coupled with density functional theory calculations suggested that the highly controlled living copolymerization is probably a consequence of the difficulty in chain transfer of VNB (or ENB)‐last‐inserted species and some characteristics of living ethylene polymerization under limited conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   

3.
    
Hydrogen is a very effective chain‐transfer agent in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts. However, measurements of the hydrogen concentration effect on the molecular weight of polypropylene prepared with a supported TiCl4/dibutyl phthalate/MgCl2 catalyst show a peculiar effect: hydrogen efficiency in the chain transfer significantly decreases with concentration, and at very high concentrations, hydrogen no longer affects the molecular weight of polypropylene. A detailed analysis of kinetic features of chain‐transfer reactions for different types of active centers in the catalyst suggests that chain transfer with hydrogen is not merely the hydrogenolysis reaction of the Ti? C bond in an active center but proceeds with the participation of a coordinated propylene molecule. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1899–1911, 2002  相似文献   

4.
    
A series of novel (arylimido)vanadium(V) complexes bearing tridentate salicylaldiminato chelating ligands, V(N‐2,6‐Me2C6H3)Cl2[(O‐2‐tBu‐4‐R‐C6H3)CH?ND] (R = H, D = 2‐CH3O? C6H4 ( 2a ); 2‐CH3S? C6H4 ( 2b ); 2‐Ph2P? C6H4 ( 2c ); 8‐C9H6N (quinoline) ( 2d ); CH2C5H4N ( 2e ); R = tBu, D = 2‐Ph2P? C6H4 ( 2f )), were prepared from V(NAr)Cl3 by reacting with 1.0 equiv of the ligands in the presence of triethylamine in tetrahydrofuran. These complexes were characterized by 1H, 13C, 31P, and 51V NMR spectra and elemental analysis. The structures of 2c and 2f were further confirmed by X‐ray crystallographic analysis. These (arylimido)vanadium(V) complexes are effective catalyst precursors for ethylene polymerization in the presence of Et2AlCl as a cocatalyst and ethyl trichloroacetate as a reactivating agent. Complex 2c with a ? PPh2 group in the sidearm was found to exhibit an exceptional activity up to 133800 kg polyethylene/molV h for ethylene polymerization at 75 °C, which is one of the highest activities displayed by homogeneous vanadium(V) catalysts at high temperature. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2633‐2642  相似文献   

5.
    
In propylene polymerization with MgCl2‐supported Ziegler‐Natta catalysts, it is known that the reduction of TiCl4 with alkylaluminum generates Ti3+ active species, and at the same time, leads to the growth of TiClx aggregates. In this study, the aggregation states of the Ti species were controlled by altering the Ti content in a TiCl3/MgCl2 model catalyst prepared from a TiCl3 · 3C5H5N complex. It is discovered that all the Ti species become isolated mononuclear with a highly aspecific feature below 0.1 wt.‐% of the Ti content, and that the isolated aspecific Ti species are more efficiently converted into highly isospecific ones by the addition of donors than active sites in aggregated Ti species.

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6.
    
Summary: A comparative study of the performances of (bpzmp)ZrBz3 ( 1 ) and (hppzm)ZrBz3 ( 2 ) activated with B(C6F5)3 or [Ph3C][B(C6F5)4] in ethylene polymerisation pointed out that the steric properties of the metal complex and the boron activator affect the productivity of the catalyst and, more remarkably, the microstructure of the polyethylenes produced. A polymerisation mechanism accounting for these results has been proposed.

Structure of two heteroscorpionate zirconium complexes (bpzmp)ZrBz3 ( 1 ) and (hppzm)ZrBz3 ( 2 ).  相似文献   


7.
    
The copolymerizations of ethylene with cyclic dienes [dicyclopentadiene (DCPD) and 2,5‐norbornadiene (NBD)] using bis(β‐enaminoketonato)titanium complexes [PhN = C(R2)CHC(R1)O]2TiCl2 ( 1a : R1 = CF3, R2 = CH3; 1b : R1 = t‐Bu, R2 = CF3; 1c : R1 = Ph, R2 = CF3) have been investigated. In the presence of modified methylaluminoxane, these complexes exhibited high catalytic activities in the copolymerization of ethylene with DCPD or NBD, affording high molecular weight copolymers with unimodal molecular weight distributions. 1H and 13C‐NMR spectra reveal ethylene/DCPD copolymerizations by catalysts 1a – c proceeds through the enchainment of norbornene ring. Catalysts 1a and 1c showed a tendency to afford alternating copolymers. More noticeably, catalysts 1b and 1c bearing bulky substituents on the ligands promote ethylene/NBD copolymerization without crosslinking, affording the copolymer containing intracyclic double bonds. The NBD incorporation as high as 27.2 mol % has been achieved by catalyst 1c . Moreover, the microstructures of the copolymers were further confirmed by the measurement of reactivity ratios and dyad monomer sequences as well as mean sequence lengths. The intracyclic double bonds of ethylene/DCPD or ethylene/NBD copolymers can be fully converted into polar groups such as epoxy, amine, silane, and hydroxyl groups under mild conditions. Convenient synthesis of hydroxylated polyethylene can be provided for the first time through the ring opening reaction of epoxide. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1764–1772, 2010  相似文献   

8.
    
A simplified kinetic scheme of eythylene/α‐olefin copolymerization has been developed by adding reactions responsible for the unusual kinetic behavior to a general mechanism. The estimation of rate constants has been simplified by making physically meaningful initial guesses. Rate constants affecting yield, MWD and comonomer content have been estimated separately. Experiments were designed to investigate the effects of each rate constant independently. The obtained rate constants show that the sites which are responsible for formation of short chains with higher 1‐butene content are more active at the beginning of polymerization, while the sites which are responsible for formation of longer chains with lower 1‐butene units are more active at the final stages of polymerization.

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9.
    
A series of novel vanadium(III) complexes bearing bidentate phenoxy‐phosphine oxide [O,P=O] ligands, (2‐R1‐4‐R2‐6‐Ph2P=O‐C6H2O)VCl2(THF)2 ( 2a : R1 = R2 = H; 2b : R1 = F, R2 = H; 2c : R1 = tBu, R2 = H; 2d : R1 = Ph, R2 = H; 2e : R1 = R2 = Me; 2f : R1 = R2 = tBu; 2g : R1 = R2 = CMe2Ph) have been synthesized by adding 1 equiv of the ligand to VCl3(THF)3 dropwise in the presence of excess triethylamine. Under the same conditions, the adding of VCl3(THF)3 to 2.0 equiv of the ligand afforded vanadium(III) complexes bearing two [O,P=O] ligands ( 3c , 3f ). All the complexes were characterized by FTIR and mass spectra as well as elemental analysis. Structures of complexes 2c and 3c were further confirmed by X‐ray crystallographic analysis. On activation with Et2AlCl and ethyl trichloroacetate, these complexes displayed high catalytic activities for ethylene polymerization (up to 26.4 kg PE/mmolV·h·bar) even at high reaction temperature (70 °C) indicative of high thermal stability, and produced high molecular weight polymers with unimodal molecular weight distributions. Additionally, the complexes with optimized structure exhibited high catalytic activities for ethylene/1‐hexene copolymerization. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled in a wide range via the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and reaction temperature. The monomer reactivity ratios rE and rH were determined according to 13C NMR spectra, which indicated these complexes preferred ethylene to 1‐hexene in the copolymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5298–5306  相似文献   

10.
    
A series of novel vanadium(III) complexes bearing tridentate phenoxy‐phosphine [O,P,O] ligands and phosphine oxide‐bridged bisphenolato [O,P?O,O] ligands, which differ in the steric and electronic properties, have been synthesized and characterized. These complexes were characterized by Fourier transform infrared spectroscopy (FTIR) and mass spectra as well as elemental analysis. Single‐crystal X‐ray diffraction revealed that complexes 3c and 4e adopt an octahedral geometry around the vanadium center. In the presence of Et2AlCl as a cocatalyst, these complexes displayed high catalytic activities up to 22.8 kg PE/mmolV.h.bar for ethylene polymerization, and produced high‐molecular‐weight polymers. Introducing additional oxygen atom on phosphorus atom of [O,P,O] ligands has resulted in significant changes on the aspect of steric/electronic effect, which has an impact on polymerization performance. 3c and 4c /Et2AlCl catalytic systems were tolerant to elevated temperature (70 °C) and yielded unimodal polyethylenes, indicating the single‐site behavior of these catalysts. By pretreating with equimolar amounts of alkylaluminums, functional α‐olefin 10‐undecen‐1‐ol can be efficiently incorporated into polyethylene chains. 10‐Undecen‐1‐ol incorporation can easily reach 14.6 mol % under the mild conditions. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, Al/V (molar ratio), and comonomer concentration, are also examined in detail. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013  相似文献   

11.
    
Novel chromium catalysts based on bidentate phenoxy‐phosphinoyl (HO‐2R1‐4R2‐6(Ph2P?O)C6H2: R1 = R2 = H, 3a ; R1 = tBu, R2 = H, 3b ; R1 = R2 = tBu, 3c ; R1 = R2 = cumyl, 3d ; R1 = anthracenyl, R2 = H, 3e ) and thiophenol‐phosphine (HS‐2R1‐4R2‐6(Ph2P)C6H2: R1 = R2 = H, 4a ; R1 = SiMe3, R2 = H, 4b ) were prepared and characterized. Treatment with modified methyaluminoxane, these catalysts displayed moderate to high‐catalytic activities for ethylene polymerization. The activities of them were higher than those of the corresponding catalysts based on bidentate phenoxy‐phosphine ligands. Both the coordinated donors and the ortho‐substituent of the ligands played an important role in improving catalytic activity. The effects of reaction parameters, such as cocatalyst and Al/Cr molar ratio as well as reaction temperature, on ethylene polymerization behaviors were investigated in detail for two favorable catalytic systems, 3b /CrCl3(thf)3 and 4b /CrCl3(thf)3. Catalyst 4b /CrCl3(thf)3 displayed higher catalytic activity and better temperature tolerance for ethylene polymerization than 3b /CrCl3(thf)3. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 311–319, 2010  相似文献   

12.
    
A series of novel vanadium(III) complexes bearing heteroatom‐containing group‐substituted salicylaldiminato ligands [RN?CH(ArO)]VCl2(THF)2 (Ar = C6H4, R = C3H2NS, 2a ; C7H4NS, 2c ; C7H5N2, 2d ; Ar = C6H2tBu2 (2,4), R = C3H2NS, 2b ) have been synthesized and characterized. Structure of complex 2c was further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a–d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmolV h bar), and affording polymer with unimodal molecular weight distributions at 25–70 °C in the first 5‐min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 °C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a–d were also explored in the presence of Et2AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled over a wide range by the variation of catalyst structure and the reaction parameters, such as comonomer feed concentration, polymerization time, and polymerization reaction temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3573–3582, 2009  相似文献   

13.
    
A series of amino‐pyrrolide ligands ( 1–4a ) and their derivatives amino‐thiophene ligand ( 5a ), amino‐indole ligand ( 6a ) were prepared. Chromium catalysts, which were generated in situ by mixing the ligands with CrCl3(thf)3 in toluene, were tested for ethylene polymerization. The preliminary screening results revealed that the tridentate amino‐pyrrolide ligands containing soft pendant donor, 3a, 4a /CrCl3(thf)3 systems displayed high catalytic activities towards ethylene polymerization in the presence of modified methyaluminoxane. The electronic and steric factors attached to the ligand backbone significantly affected both the catalyst activity and the polymer molecular weight. Complex 4b was obtained by the reaction of CrCl3(thf)3 with one equivalent of the lithium salts of 4a , which was the most efficient ligand among the tested ones. The effect of polymerization parameters such as cocatalyst concentration, ethylene pressure, reaction temperature, and time on polymerization behavior were investigated in detail. The resulting polymer obtained by 4b display wax‐like and possess linear structure, low molecular weight, and unimodal distribution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 713–721, 2009  相似文献   

14.
    
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15.

The MCM‐41 and SiO2 supported TiCl4 and TiCl4/MgCl2 catalysts with different molar ratios of Mg/Ti were synthesized and used for ethylene polymerization under atmospheric pressure. The nanochannels of MCM‐41 serve as nanoscale polymerization reactor and the polyethylene nanofibers were extruded during the reaction. The nanofibers were observed in SEM micrographs of resulting polyethylene. The effect of MgCl2 on catalytic activity and thermal properties of resulting polyethylene is investigated too. In the presence of MgCl2, the catalytic activity increased and more crystalline polyethylene with higher melting points were formed. However, no fibers could be observed in the polyethylene prepared by SiO2 supported catalysts.  相似文献   

16.
    
Vanadium complexes with tetradentate salen‐type ligands were first time explored in ethylene polymerizations. The effects of the vanadium complex structure, the alkyl aluminum cocatalysts type (EtAlCl2, Et2AlCl, Et3Al, and MAO), and the polymerization conditions (Al/V molar ratio, temperature) on polyethylene yield were explored. It was found that EtAlCl2 in conjunction with investigated vanadium complexes produced the most efficient catalytic systems. It was shown, moreover, that the structural changes of the tetradentate salen ligand (type of bridge which bond donor nitrogen atoms and type of substituent on aryl rings) affected activity of the catalytic system. The complexes containing ligands with cyclohexylene bridges were more active than those with ethylene bridges. Furthermore, the presence of electron‐withdrawing groups at the para position and electron‐donating substituents at the ortho position on the aryl rings of the ligands resulted in improved activity in relation to the systems with no substituents (with the exception of bulky t‐Bu group). The results presented also revealed that all vanadium complexes activated by common organoaluminum compounds gave linear polyethylenes with high melting points (134.8–137.6 °C), high molecular weights, and broad molecular weight distribution. The polymer produced in the presence of MAO possesses clearly lower melting point (131.4 °C) and some side groups (around 9/1000 C). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6940–6949, 2008  相似文献   

17.
    
A series of (SiO2/MgO/MgCl2)?TiClx Ziegler‐Natta polyethylene catalysts have been synthesized using water‐soluble Mg‐compounds such as magnesium acetate as Mg‐source at different TiCl4 treating temperatures. The catalyst shows the highest activity of homopolymerization when preparation temperature is 120 °C with only 1.25 of optimal Al/Ti molar ratio, which is much lower than industrial value, resulting in much lower catalyst preparation and poly­ethylene production cost. The operation condition is relatively moderate and the synthesized catalysts exhibit rather high activity, good hydrogen response, and copolymerization ability with high 1‐hexene incorporation. The polymers obtained from these catalysts have high molecular weight and medium molecular weight distribution. Compared with the conventional industrial Ti/Mg Ziegler‐Natta catalysts using the relatively expensive, anhydrous and moisture‐sensitive Mg‐sources, the most unique feature of our novel catalysts is the capability of utilization of any soluble Mg‐compounds under mild conditions and can achieve rather high activity with only a small amount of cocatalyst, hence show great potential for application in polyethylene industry.

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18.
    
This article compares catalytic performance of ethylene polymerization in similar polymerization conditions of transition metal complexes having two ligands [O,N] (phenoxy‐imine) and having one tetradentate ligand [O,N,N,O] (salphen or salen). It is shown that the activity of both complex types as well as the product properties depend in the same way on the type of central metal in the complex and on the cocatalyst used. Although the type of ligand has some effect on the catalyst activity, yet it does not control the properties of the obtained products. The vanadium and zirconium complexes, irrespective of the cocatalyst used, yield linear polyethylene with high molecular weight (a few hundred thousand g/mol). Similar products are formed when titanium complexes activated with MAO are employed. On the other hand, the same titanium complexes in conjunction with Et2AlCl, yield low molecular weight polyethylene (of a few thousand) and additionally a mixture of oligomers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 565–575, 2009  相似文献   

19.
The gas-phase ethylene polymerizations with SiO2-supported Ziegler–Natta (ZN) catalyst at early moments of reaction is modeled. The experimental data used in this work show that at initial stages of the polymerization there is a sharp reduction in the reaction rate and a sharp rise in molecular weight. In the modeling, multi-active sites assumption and diffusion limitations inside the particle are studied. Energy balance to calculate the temperature at early moment is applied. Kinetic model including initiation, propagation, chain transfers and active site deactivation steps are used to predict the reaction rate and molecular weights. Polymeric flow model (PFM) is applied for single particle model (SPM). The results show two distinct regions. First region with sharp gradient for reaction rate and molecular weights and then, shortly there is a smooth region in which the changes in rate and molecular weights are slow. To fit this sharp gradient followed by a nearly steady state behavior two types of active sites are necessary. A group of highly active sites which deactivated soon and the active sites with lower activity and relatively long-lasting.  相似文献   

20.
    
Iminopyrrolyl vanadium(III) complexes 2a–b bearing tridentate ligands [C4H3NCH?NC6H4L]VCl2(THF) [L = 2‐P(C6H5)2 ( 2a ), 2‐SMe ( 2b )] and complexes 2c–d with tetradentate ligands [(C4H3NCH?N)2R]VCl(THF) [R = 1,2‐C6H4 ( 2c ), 1,2‐C2H4 ( 2d )] have been synthesized in high yields. With diethylaluminium chloride as a cocatalyst, complexes 2a–d were investigated as efficient catalysts for ethylene polymerization under various reaction conditions, and exhibited high catalytic activity and remarkable thermal stability. With these complexes, high molecular weight polymers with unimodal molecular weight distributions were obtained, indicating that the polymerization reaction took place in a single‐site nature. Ethylene/1‐hexene copolymerizations were also investigated in the presence of Et2AlCl. Both increasing ligand denticity and introducing softer atom into the sidearm of the ligands significantly influenced catalytic activity, comonomer incorporation, and the molecular weights of the resultant polymers, suggesting that both the steric and the electronic effects of the ligands played an important role in adjusting chain propagation and transfer rate. The chain transfer mechanisms involved in the copolymerization process were investigated by carefully analyzing the microstructure of the copolymers. The signals of vinyl, disubstituted and tri‐substituted vinylene double bond end groups were detected in the copolymer obtained by 2a /Et2AlCl system but not in those by 2b–c /Et2AlCl systems, indicating that bulky electron‐donating group, ? P(C6H5)2, may lead to those unusual transfer reactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   

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