Polymerization of methyl methacrylate with Ni(acac)2–methylaluminoxane catalyst

Polymerization of methyl methacrylate (MMA) with nickel(II) acetylacetonate [Ni(acac)₂] in combination with methylaluminoxane (MAO) was investigated. Ni(acac)₂ was found to be an effective catalyst for the polymerization of MMA. From a kinetic study of the polymerization of MMA with the Ni(acac)₂–MAO catalyst, the overall activation energy was estimated to be 15 kJmol⁻¹. The polymerization rate (R_p) was expressed as follows: R_p = k [MMA]^1.0[Ni(acac)₂–MAO]^0.6 (the MAO/Ni mole ratio was kept constant). The mechanism for the polymerization of vinyl monomers with the Ni(acac)₂–MAO catalyst is discussed. © 2000 Society of Chemical Industry     

Comparative study of homogeneous and heterogeneous styrene polymerizations with Ni(acac)2/MAO catalytic system

Styrene polymerization was carried out with Ni(acac)₂/MAO and Ni(acac)₂/SiO₂/MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type.     

Recycling of methylaluminoxane (MAO) cocatalyst in ethylene polymerization with supported metallocene catalyst

The economy of the metallocene catalyst system in olefin polymerization depends more on the cost of methylaluminoxane (MAO) cocatalyst rather than on the catalyst cost since high ratio of cocatalyst to catalyst is required to have sufficient activity. The conditions to minimize the consumption of MAO have been studied for the ethylene polymerization with supported metallocene catalyst. By introducing the prepolymerization step, in which the supported metallocene catalyst is activated at high MAO concentration before polymerization, the MAO could be recovered after the prepolymerization and recycled repeatedly for the subsequent activation with marginal decrease in activity. No extra MAO was needed during the main polymerization. The addition of small amount of MAO or less expensive alkylaluminum at each recycle step kept the catalyst activity to the initial level. It compensates the MAO losses occurring both by the incomplete decantation of MAO solution and by the reaction with metallocene complex or impurities. As a result, the actual consumption ratio of Al/Zr in moles in commercial applications could be reduced to about 30 without sacrificing the activity. This value is significantly low considering that conventionally an Al/Zr ratio of 1,000 is required for sufficient activity. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

IRS study of ethylene polymerization catalyst SiO2/MAO/zirconocene

Summary Lewis acidic sites (LAS) of silica, modified with TMA and MAO samples differed by TMA content, have been characterized by IR spectroscopy (CO adsorption as probe molecule at 77 K). Two types of LAS were found on the surface of silica modified with MAO and TMA: M LAS of moderate strength (ν_CO= 2204−2212 cm⁻¹) and weak W LAS (ν_CO= 2194 cm⁻¹). The concentration of these acidic sites has been estimated. It was shown by IRS study Cp₂ZrMe₂ interacts both with W LAS and M LAS. Correlation between the amount of M LAS and the activity of ethylene polymerization has been found. Received: 13 October 1998/Revised version: 10 June 1999/Accepted: 10 June 1999     

Reverse atom transfer radical polymerization of styrene initiated with AIBN/Ni ( naph ) 2/PPh3 catalyst system

以AIBN/Ni(naph),/PPh3为均相引发剂引发苯乙烯聚合,所得试样相对分子质量与转化率呈线性增加,相对分子质量分布约为1.5.紫外光谱分析表明,聚合机理为反向原子转移自由基聚合.     

Syndiotactic polymerization of styrene with CpTiCl2(OPri)/methylaluminoxane

Summary CpTiCl₂(OPrⁱ) was a very active catalyst for syndiotactic polymerization of styrene when activated with methyl aluminoxane (MAO). The catalyst activity and syndiospecificity of CpTiCl₂(OPrⁱ)/MAO were about 10⁷ g PS / mol Ti·mol S·h and about 95% respectively, both higher than those of CpTiCl₃ / MAO.     

Novel monotitanocene and methylaluminoxane catalyst for syndiospecific polymerization of styrene

Syndiotactic polystyrene (sPS) was synthesized with a novel monotitanocene complex of η⁵‐pentamethylcyclopentadienyltri‐4‐methoxyphenoxy titanium [Cp*Ti(OC₆H₄OCH₃)₃] activated by methylaluminoxane (MAO) in different polymerization media, including heptane, toluene, chlorobenzene, and neat styrene. In all cases bulk polymerization produced sPS with the highest activity and molecular weight. Solution polymerization produced much better activity in heptane than in the other solvents. Using a solvent with a higher dipole moment, such as chlorobenzene resulted in lower activity and syndiotacticity because of the stronger coordination of solvent with the Ti(III) active species, which controlled syndiospecific polymerization of styrene. With bulk polymerization at a higher polymerization temperature the Cp*Ti(OC₆H₄OCH₃)₃–MAO catalyst produced sPS with high catalytic activity and molecular weight. The external addition of triisobutylaluminum (TIBA) to the Cp*Ti(OC₆H₄OCH₃)₃–MAO system catalyzing styrene polymerization led to significant improvement of activity at a lower Al:Ti molar ratio, while the syndiotacticity and molecular weight of the yields were little affected. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1243–1248, 2001     

Syndiospecific polymerization of styrene based on dichlorobis(1,3‐diketonato)titanium/methylaluminoxane catalyst system: effects of substituents on catalyst activity

Dichlorobis(substituted‐1,3‐diketonato)titanium complexes 4a–e have been synthesized and were combined with methylaluminoxane as cocatalyst to be employed in the polymerization of styrene. The polystyrenes produced have high syndiotacticities of 94.0–98.2%. The substituents at either 2‐ or 1,3‐positions of 1,3‐diketones can noticeably influence catalyst activities. The catalytic activities of 4a–c bearing 2‐substituents and 4e bearing 1,3‐diphenyl groups are tenfold higher than that of 4d bearing 1,3‐dimethyl groups. The effects of polymerization conditions on the catalyst activities and the syndiotacticities of the polystyrene produced have been examined. © 2000 Society of Chemical Industry     

Copolymerization of styrene and methyl methacrylate with nickel acetylacetonate/methylaluminoxane catalyst system

The present work deals with copolymerization of styrene (STY) and methyl methacrylate (MMA) catalysed by nickel acetylacetonate - Ni(acac) ₂ , employing methylaluminoxane (MAO) as cocatalyst. This catalyst system presented low catalyst activities for STY homopolymerization and very high activities for MMA. It seems that the catalyst system based on Ni(acac) ₂ /MAO is effective for the copolymerization of MMA and STY to give block copolymer but it also produced polystyrene and poly(methyl methacrylate) homopolymers. The polymers were characterized by ¹³ C NMR, GPC and FTIR. The polystyrene homopolymer was identified by IR and NMR analyses of the cyclohexane soluble fraction. The presence of absorption bands correspondent to carbonyl group and aromatic ring was observed in the IR spectrum of the acetic acid soluble part. This result is a clue that STY-MMA copolymer with low molecular weight was produced. The high molecular weight copolymer (acetic acid insoluble fraction) was also characterized by IR analysis which indicated the presence of characteristic absorption bands of carbonyl group and aromatic ring. These results were confirmed by ¹³ C NMR analysis. Received: 6 August 1997/Revised version: 29 December 1997/Accepted: 7 January 1998     

Characterization of polyethylene/kaolin composites by polymerization filling with Cp2ZrCl2/MAO catalyst system

In this work, the preparation and characterization of metallocene‐catalyzed polyethylene (PE)/kaolin composites were presented. The composites was prepared by the so‐called polymerization‐filling method in which the PE matrix was formed directly on the kaolin surface by ethylene polymerization with the prefixed Cp₂ZrCl₂/methylaluminoxane (MAO) catalyst system on the kaolin surface. SEM, FTIR, and DMA were carried out to characterize the composites. The experimental results showed the new composites had homogeneous distribution of kaolin particles in the PE matrix and strong interfacial interaction between the PE matrix and kaolin particles. At the molecular level, the interfacial interaction caused the decrease of the mobility of PE molecular chains. In addition rheological testing showed that the introduction of kaolin by polymerization filling could improve the rheological behavior of prepared composites. The relationship between the rheological behaviors and the interfacial conditions were discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2913–2921, 2002     

Isospecific polymerization of styrene with supported nickel acetylacetonate/methylaluminoxane catalysts

Summary The polymerization of styrene with catalysts based on Ni(acac)₂ supported on SiO₂ and Al₂O₃ was investigated. Using catalysts based on MAO supported on silica, a highly isotactic polystyrene was obtained. Nevertheless, the Al₂O₃-supported catalyst can promote isospecific polymerization activated by common. alkyl aluminum compounds even by any prior support treatment with MAO. Received: 3 March 1998/Revised version: 14 April 1998/Accepted: 14 April 1998     

Syndiotactic polymerization of methyl methacrylate with Ni(acac)<Subscript>2</Subscript>-methylaluminoxane catalyst

In this study, syndiotactic-rich poly(methyl methacrylate) (PMMA) is obtained by using a soluble nickle acetylacetonate [Ni(acac)₂] and modified methylaluminoxane (MMAO-3A) catalyst system under modest polymerization conditions. The main purpose of this work is concerned with the study of previous conflicting stereospecificity data. Types of MAO, temperature of polymerization, MAO/Ni(acac)₂ (Al/Ni) mole ratio, and various solvents have been investigated in the MMA polymerization. Particularly, high syndiotactic PMMA [(rr) > 91 %] has been obtained when MMAO-3A is used as cocatalyst with Al/Ni ratio of ca. 50 or polymerization temperature ca. 0 °C. As expected, the prepared syndiotacticity-rich PMMA has a higher glass transition temperature (T _g) within 120 ~ 127 °C. The details of the polymerization mechanism, especially in relation to the stereoregularity problems are under investigation.     

Poisoning effect of CO on ethylene polymerization with Ni(II)-diimine/MAO

CO was not a comonomer but an inhibitor in ethylene polymerization catalyzed over [1,2-bis(2,6-diisopropylphenylimino)]acenaphthene nickel(II) dibromide (1)/MAO. The average number of active sites, , and the average rate constant for chain propagation, of the (1)/MAO system was determined using CO inhibition method based on the assumption that two molecules of CO coordinate to each active center. At 0 °C, the average number of active centers, , was increased with the Al/Ni ratio, and , was not influenced by the Al/Ni ratio. Up to Al/Ni ratio of 3000, the average number of active sites was saturated. Single active site was present at the high ratio of Al/Ni and its reactivity with CO is uniform at 0 °C. The maximum average activity was 5262.07 (kg-PE/mol-Ni/atm/hr) and 65.7% of (1) was converted to form active cation complexes at 0 °C and Al/Ni molar ratio of 5000, while 36.5% of (1) was activated at the Al/Ni molar ratio of 250. Above 30 °C, the complicated CO poisoning behavior was observed because the reactivity and stoichiometry of active centers with CO were not uniform and their thermal stability was very poor.     

Mono-aryloxy or mono-alkoxy zirconium complexes/methylaluminoxane catalyst system in ethylene polymerization

Summary Mono-aryloxy zirconium complexes 1–6 or mono-alkoxy zirconium complexes 7–10 were prepared and the ethylene polymerization was carried out in the presence of these complexes/methylaluminoxane. Steric factor of the aryloxy and alkoxy ligands in the complexes remarkably influenced on activity of ethylene polymerization.     

Molecular-weight-controlled polymerization of styrene with Mn(acac)3 in combination with organic halides

Summary The control of molecular weight of polymers in polymerization of styrene (St) with manganese(III) acetylacetonate [Mn(acac)₃] in the presence of organic halides (RX) in toluene at 80°C was investigated. In the polymerizations of St with Mn(acac)₃ in combination with benzyl bromide (BzBr) as RX, the molecular weight of the polymer increased with polymer yields, and the relationships between the molecular weight of polymer and polymer yield gave a straight line passing through the original point. However, the molecular weight distribution was not narrow, but kept almost constant (M_w/M_n was about 2) throughout the polymerization. The mechanism of the polymerization of St with Mn(acac)₃-BzBr was also discussed. Received: 18 December 2000/Revised version: 19 April 2001/Accepted: 25 April 2001     

甲基铝氧烷对稀土催化体系催化异戊二烯聚合的影响

考察了甲基铝氧烷(MAO)作为助催化剂对稀土催化体系催化异戊二烯聚合的影响,结果表明MAO可极大地提高体系的催化活性,获得顺-1,4结构含量95%(质量分数)以上的聚异戊二烯,并且调节n(MAO)/n(Nd)和n(Al)/n(Nd)的值可有效地提高聚合产物的相对分子质量.     

Fe(acac)3‐bis(imino)pyridine/MAO: A new catalytic system for ethylene polymerization

Formulations of chemically crosslinked and radiation-crosslinked low-density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with poly(ethylene vinyl acetate) (EVA) as well as the effects of a coadditive such as talc on flammability was investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron-beam accelerator were both used and compared. An increase in the limiting oxygen index (LOI) was found by the partial replacement of LDPE with EVA. The effect of talc on the flammability depended on the amount of talc in the formulations. The addition of a small amount of talc increased LOI and reduced smoke during cone calorimeter measurements. A higher amount of talc led to a decrease in the LOI values. Formulations crosslinked by ionizing radiation yielded lower LOI values than chemically crosslinked formulations. This could be attributed to the use of trimethylolpropane triacrylate as a crosslinking coagent in formulations crosslinked by ionizing radiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

SiO2负载二亚胺镍/TiCl4催化乙烯聚合

合成了配合物N,N'-二[4-(4-氨基-3,5-二乙基苄基)-2,6-二乙基苯基]苊二亚胺二氯化镍(NiLCl2),将其与TiCl4复合负载在SiO2/MgCl2上制得负载催化剂.研究了该负载催化剂对乙烯聚合的催化活性, 考察了聚合条件对聚合反应及产物结构的影响.结果表明,负载的NiLCl2/TiCl4较之未负载的NiLCl2催化活性高,最高催化活性达到552 kg/(mol·h),而聚合需要的n(Al)/n(Ni)也较相应的NiLCl2低.     

Bulk polymerization of vinyl chloride with half-titanocene/MAO catalyst

Bulk polymerization of vinyl chloride (VC) with Cp^∗Ti(OPh)₃/MAO catalyst was investigated. The bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst proceeded to give poly(vinyl chloride) (PVC) with high molecular weight in good yields. The M_n of the polymer increased in direct proportion to polymer yields and the line passed through the origin. The M_w/M_n of the polymer decreased with an increase of polymer yield. The GPC elution curves were unimodal and the whole curves shifted clearly to the higher molecular weight as a function of reaction time. This indicates that the control of molecular weight can be achieved in the polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst even in bulk. The structure of PVC obtained from the bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst consists of a regular structure. The thermal stability of the polymer obtained with Cp^∗Ti(OPh)/MAO catalyst was higher than that of PVC obtained from radical polymerization and depended on the molecular weight of the polymer. In contrast to that, the initial decomposition temperature of the polymer obtained from a radical polymerization did not depend on the molecular weight. We presumed that the decomposition of the polymer obtained with Cp^∗Ti(OPh)₃/MAO catalyst initiated at the chain end.     

Atom transfer radical polymerization of styrene with FeCl2/acetic acid as the catalyst system

Summary Atom transfer radical polymerization with FeCl₂/CH₃COOH as the catalyst has been successfully implemented for styrene. Various initiators have been used, among which carbon tetrachloride is the most effective one. High molecular weight products were obtained when CCl₄ was used as the initiator, and the measured molecular weight was close to the calculated one. Block copolymerization (PS-b-PMMA) was performed to confirm the living/controlled nature of the polymerization. ¹H NMR was used to characterize the structure of the macromolecular initiator and the block copolymer. If other initiators, such as benzyl bromide, ethyl 2-bromopropionate and α-bromoethyl benzene, were used, the polymerization occurred at ambient temperature resulting in oligomer. The molecular weight of the oligomer approaches to 4600 (M_n,th= 10000). Thus acetic acid, which is cheaper and less toxicity, can be used as coordinative ligand in ATRP initiated by CCl₄ mediated by iron. Received: 13 March 2000/Revised version: 13 November 2000/Accepted: 20 November 2000