Homogeneous neodymium iso-propoxide/modified methylaluminoxane catalyst for isoprene polymerization

The neodymium iso-propoxide [Nd(Oi-Pr)₃] catalyst activated by modified methylaluminoxane (MMAO) is homogeneous and effective in isoprene polymerization in heptane to provide polymers with high molecular weight (M_n∼10⁵), narrow molecular weight distribution (M_w/M_n=1.1-2.0) and mainly cis-1,4 structure (82-93%). The polymer yield increased with increasing [Al]/[Nd] ratio (50-300 mole ratio) and polymerization temperature (0-60 °C), while the molecular weight and cis-1,4 content decreased. On the other hand, the same catalyst resulted in relatively low polymer yield and low molecular weight in toluene. The cyclized polyisoprene was formed in dichloromethane, which is attributable to the cationic active species derived from MMAO alone. When chlorine sources (Et₂AlCl, t-BuCl, Me₃SiCl) were added, the cis-1,4 stereoregularity of polymer improved up to 95% even at a high temperature of 60 °C, though the polymer yield decreased.     

Methylaluminoxane‐activated neodymium chloride tributylphosphate catalyst for isoprene polymerization

The polymerization of isoprene was examined by using a novel binary catalyst system composed of neodymium chloride tributylphosphate (NdCl₃·3TBP) and methylaluminoxane (MAO). The NdCl₃·3TBP/MAO catalyst worked effectively in a low MAO level ([Al]/[Nd] = 50) to afford polymers with high molecular weight (M_n ～10⁵), narrow molecular weight distribution (M_w/M_n = 1.4–1.6), and high cis‐1,4 stereoregularity (> 96%). The catalytic activity increased with an increasing [Al]/[Nd] ratio from 30 to 100 and polymerization temperature from 0 to 50°C, while the M_n of polymer decreased. The presence of free TBP resulted in low polymer yield. Polymerization solvent remarkably affected the polymerization behaviors; the polymerizations in aliphatic solvents (cyclohexane and hexane) gave polymer in higher yield than that in toluene. The M_w/M_n ratio of the producing polymer remained around 1.5 and the gel permeation chromatographic curve was always unimodal, indicating the presence of a single active site in the polymerization system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40153.     

均相Nd(Oct)3/Al(i-Bu)3/AlCl3用于异戊二烯聚合

采用Nd(Oct)3、Al(i-Bu)3、AlCl3,AlCl3溶解于Al(i-Bu)3中配制成一定浓度的溶液作为氯配体。Nd(Oct)3与AlCl3在室温(20℃)下反应后,再加入一定量的Al(i-Bu)3,可配制成均相高效催化剂体系。所得聚合物同时具备顺-1,4含量高(96%)、高分子质量(105)、相对较窄的分子质量分布(Mw/Mn=2.1~3.0)等特征。更重要的是,证明了一些活性聚合的特征:a)无链终止反应;b)Mn和转化率线性相关;c)种子聚合中分子质量逐渐增加。虽然与典型的种子聚合有一些偏离,比如分子质量分布稍宽,Mn~转化率曲线不过原点,但仍然可认为是可控聚合。     

A convenient method for the preparation of a highly active SiO2-supported CoCl2 catalyst for the polymerization of isoprene

Summary A highly dispersed SiO₂-supported CoCl₂ catalyst was prepared by supporting the complex of CoCl₂ 2C₅H₅N on SiO₂ in n-heptane, followed by evacuating at room temperature. The catalyst combined with AlEt₂Cl showed a very high activity for the polymerization of isoprene.     

用脂肪烃溶液型磷酸酯稀土催化剂合成高顺式聚异戊二烯

在三(2-乙基己基)磷酸酯钕的己烷溶剂中加入少量二氯二甲基硅烷,对其在己烷溶剂中形成的低聚物解缔合,制备出溶液型磷酸酯钕。以溶液型磷酸酯钕Nd(P_(204))_3(简称Nd)/烷基铝(简称Al)/氯化合物(简称Cl)催化体系催化异戊二烯聚合,考察了不同烷基铝、氯源种类、Al/Nd、Cl/Nd及聚合温度对异戊二烯聚合的影响。结果表明,用Nd/Al(i-Bu)_3/Al(i-Bu)_2Cl催化体系制备的聚合物相比于Nd/Al(i-Bu)_2H/Al(i-Bu)_2Cl体系具有更高的分子量,两种催化体系均可制得具有高顺式-1,4-结构含量、窄分子量分布的聚异戊二烯。     

Emulsion polymerization of isoprene. Estimation of the branching exponent with the help of a mathematical model

This work investigates a batch and unseeded emulsion polymerization of isoprene at 10°C with n‐dodecylmercaptan as chain transfer agent (CTA). The obtained polyisoprene (PI) was analyzed by size exclusion chromatography (SEC) with on‐line viscometry. A global polymerization model was adjusted to the measurements of conversion, average particle size, and average molecular weights. The CTA concentration strongly affects the average molecular weights but has a negligible effect on conversion, average particle diameter, and average branching. Due to the combined effects of chain transfers to the polymer and to the CTA, the final molar mass distributions exhibited dispersity indexes higher than 10. The polymerization model predictions on the average degree of branching was combined with an ideal SEC model for adjusting the branching exponent of PI in tetrahydrofuran at 25°C that resulted ε = 2.5. A sensitivity analysis showed that +20% errors in _w induced variations in ε lower than ?10%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ethylene polymerization using a novel MgCl2/SiO2‐supported Ziegler–Natta catalyst

A novel MgCl₂/SiO₂‐supported Ziegler–Natta catalyst was prepared using a new one‐pot ball milling method. Using this catalyst, polyethylenes with different molecular weight distributions were synthesized. The effects of the [Si]/[Mg] ratio, polymerization temperature and [Al]/[Ti] ratio on the catalytic activity, the kinetic behaviour and the molecular weight and the polydispersity of the resultant polymer were studied. It was found that the polydispersity index of the polymer could be adjusted over a wide range of 5–30 through regulating the [Si]/[Mg] ratio and polymerization temperature, and especially when the [Si]/[Mg] ratio was 1.70, the polydispersity index could reach over 25. This novel bi‐supported Ziegler–Natta catalyst is thus useful for preparing polyethylene with a required molecular weight distribution using current equipment and technological processes. Copyright © 2005 Society of Chemical Industry     

A supported titanium postmetallocene catalyst: Effect of selected conditions on ethylene polymerization

Ethylene polymerization with a titanium complex [N,N‐ethylenebis(3‐methoxysalicylideneiminato)titanium dichloride] immobilized on the magnesium support with the formula MgCl₂(THF)_0.32(Et₂AlCl)_0.36 was studied. In particular, the effects of polymerization temperature, monomer pressure, and polymerization time on the activity of the catalyst and on the polyethylene properties (molecular weight and its distribution, melting point, crystallinity, and bulk density) were evaluated. The findings of investigations prove that the studied supported titanium catalyst is highly active in ethylene polymerization, and its activity increases with increasing temperature and monomer pressure. Moreover, stability of the catalytic systems is dependent on the activator type used. Me₃Al, when employed as an activator, makes the catalytic system undergo no deactivation in practice. The catalyst coupled with MAO turned out less stable. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ethylene polymerization process with a highly active Ziegler-Natta catalyst: 2. Molecular weight regulation

This paper deals with molecular weight regulation and molecular weight distribution in ethylene polymerization, using a highly active Ziegler-Natta catalyst. The molecular weight regulation can be described by equations derived in a previous paper. The development of the molecular weight distribution with reaction time showed that there must exist active sites with an overall propagation rate constant of at least 2.9 × 10³ dm³/mol sec at 85°C. This value is higher by a factor of approximately 40 than the value determined by kinetic experiments.     

Studies on propylene polymerization with a highly active MgCl2 supported TiCl4 catalyst system

Summary Propylene polymerization was performed with a highly active MgCl supported TiCl₄ in conjunction with Et₃Al and ethyl benzoate (EB). The obtained polypropylene sample was separated into four fractions by successive extraction with pentane, heptane and trichloroethylene (trichlene). Yield, Mn, Tm and microtacticity of each fraction were determined, and the effects of the concentration of EB on these items of results were investigated. It has been found that EB enhances yield, Mn and stereospecificity of trichlene insoluble (the most stereospecific) fraction, and in contrast, it decreases rapidly yields of other three fractions without changing the character of the polymers. From these findings, the functions of EB to the active centers were discussed.     

Kinetics study of slurry-phase propylene polymerization with highly active Mg(OEt)2/benzoyl chloride/TiCl4 catalyst

Propylene was polymerized in a slurry phase over superactive and stereospecific catalyst prepared by the reaction of Mg(OEt)₂ with benzoyl chloride and TiCl₄ in the presence of AlEt₃ with or without an external donor. A kinetic analysis of propylene polymerization was carried out. The polymerization rate was first order with respect to monomer concentration and the dependence of overall polymerization rate on the concentration of AlEt₃ can be explained by the Langmuir adsorption mechanism. Maximum activity was observed around an Al/Ti mole ratio of 20. The average rate over 90 min of polymerization as a function of temperature showed a maximum around 42°C and the overall activation energy was 8.5 kcal/mol at T < 42°C and ?4.0 kcal/mol at T > 42°C. The analysis of the phenomenon of an optimum temperature gave 2.2 kcal/mol for the activation energy of the rate-determining step, and 6.3 kcal/mol, for the adsorption energy of AlEt₃. The addition of small amount of p-ethoxyethyl benzoate (PEEB) as an external donor increased the percentage of isotactic polymer to 98% and slightly increased activity in spite of the decrease in the concentration of active centers due to the stabilizing effect of the active centers by the external donor. The temperature showing maximum yield was shifted to the higher temperature when AlEt₃ and PEEB ([AlEt₃]/[PEEB] = 5) was used as a cocatalyst. © 1994 John Wiley & Sons, Inc.     

Seeding as a means of controlling particle size in dispersion polymerization

Two distinctively different seeded dispersion polymerization processes employing micron and submicron size seed particles, respectively, have been used to gain a better mechanistic understanding of the dispersion polymerization process. Using monodisperse micron-size PMMA particles as seed, it was found that when low monomer/polymer ratios (M/P < 2.50) were used in methyl methacrylate (MMA) seeded dispersion polymerizations, particle growth dominates and the number of particles remains unchanged (i.e., narrow distributions are preserved). However, when higher M/P ratios (>2.50) were applied, bimodal or trimodal particle size distributions were produced, which is considered to result from the competition between particle growth and secondary nucleation. When small amounts of submicron seeds were used with the initial intention of gaining a better understanding of the nucleation process, it was surprisingly found that the final number of micron size particles was nearly the same as the initial number of submicron seed particles over a relatively wide range of reaction conditions, including seed, initiator, stabilizer, and monomer concentrations, and the medium composition. These results indicate that within certain limits seeded dispersion polymerization can be a more robust means of controlling particle size than ab initio dispersion polymerization in terms of reproducibly producing a target particle size. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

The kinetic evidence for the formation of multiple active species in a bis(phenoxy-imine) zirconium dichloride/MAO catalyst during ethylene polymerization

The effects of polymerization time and temperature on the molecular weight and molecular weight distribution of polyethylene, produced over homogeneous catalyst bis[N-(3-tert-butyl salicylidene)anilinato]zirconium(IV) dichloride ^tBu-L₂ZrCl₂/MAO have been studied. The data on the number of active centers (C_P) and propagation rate constants (k_P) at different polymerization time have been obtained as well. It was found that at a short polymerization time two types of active centers, producing low molecular weight PE (M_w = (4-10) × 10³ g mol⁻¹) are formed. The number of these centers was estimated to be 11% of total zirconium complex and their reactivity is very high (the k_P value was found to be 54 × 10³ L mol⁻¹ s⁻¹ at 35 °C). High initial activity of the catalyst fell with the increase in polymerization time, whereas the polydispersity values of the resulting PE increase due to formation of new centers, producing high molecular weight PE (M_w = (30-1300) × 10³ g mol⁻¹). It was found that the decrease in activity is caused by reducing the initial active centers number and lower reactivity of the new-formed centers (k_P = 17 × 10³ L mol⁻¹ s⁻¹).     

尤尼帕工艺用钒系催化剂的开发

钒系催化剂是尤尼帕 PE 工艺第三代催化剂,在钒系催化剂作用下,可以生产出具有宽分子量分布及双峰分子量分布的聚乙烯树脂。当加入分子量调节剂,如含氧、含硅或含磷化合物时,树脂的分子量可以由宽变窄,密度也可在一广阔的范围内变化。本文综述了联合碳化物公司钒系催化剂的最新发展,其配方及在烯烃聚合中的应用.     

Double-external-field enables bulk controlled radical polymerization with narrow molecular weight distribution at high conversion

To control over molecular weight and its distribution in bulk controlled radical polymerization (CRP) at high conversion remains a challenge. Currently, there are few reports about bulk CRP regulated by external field. In this work, a new strategy combining external fields of light and ultrasound, namely double-external-field, is reported to overcome the challenge. Light irradiation directly reduces the deactivator Cu^IIBr₂/L in the presence of free amine ligand, while ultrasonic agitation improves the homogeneity of the system and moderates the diffusional limitations on activation-deactivation and termination processes. Bulk polymerizations of methyl acrylate (MA) were conducted in a controlled manner at conversion over 90%, producing PMA with low dispersities (Đ = 1.05–1.07) and good retention of chain-end functionality (77%). In addition, good control over the polymerizations for methyl methacrylate (MMA) and styrene was obtained, although the chain-end functionality of PMMA-Br requires further improvement. It is believed that this as-developed double-external-field regulation strategy is also applicable to other light induced bulk RDRP systems to improve the controllability.     

中分子量聚乙烯齐格勒-纳塔催化剂的研究

合成了一种钛系齐格勒-纳塔烯烃聚合催化剂，该催化剂具有较高的乙烯聚合活性，其乙烯聚合动力学平稳，氢调敏感,所得到的乙烯聚合物具有中等分子量分布。     

Non-steady-state model for kinetics of free radical polymerization, 2. Redox initiation

This work deals with the non-steady-state kinetics of free radical polymerization with redox initiation. Rigorous expressions for the radical concentration, monomer conversion, molecular size distribution function, and number-average and weight-average molecular weights, etc., were derived. The molecular parameters of the resulting polymer were evaluated in relation to the polymerization conditions.     

Control of molecular weight distribution in propylene polymerization with Ziegler–Natta/metallocene catalyst mixtures

Propylene polymerization was investigated with a sequential addition of Ziegler–Natta and metallocene catalysts. From the fact that the molecular weights of polypropylene (PP) produced with Ziegler–Natta and with metallocene catalysts differ, it was possible to control the molecular weight distribution (MWD) of PP with a sequential addition of methylaluminoxane and rac-ethylenebis(indenyl)zirconium dichloride followed by triethylaluminum and magnesium dichloride-supported titanium tetrachloride catalyst. The obtained PP exhibited a wide MWD curve with shoulder peak. The position and height of each peak was controlled with the variation of polymerization time for each catalyst as well as the amount of each catalyst. The MWD of PP prepared with sequential addition of catalysts was much wider than that of PP obtained from each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2213–2222, 1998     

Modeling of sequence length distribution for olefin copolymerization with vanadium-based catalyst

Some thermodynamic and mechanical properties of a polyolefin, such as the melting temperature and the rigidity, are dependent on the nature of its sequence distribution. Accurate modeling of sequence length distribution (SLD) is important in precisely tuning and optimizing the properties of polymers produced. In this article, we proposed a model to predict the molecular weight distribution (MWD) and SLD for olefin copolymerization with vanadium-based catalyst. Due to the 2,1-insertion of α-olefin with vanadium-based catalyst, the SLD is expressed by uninterrupted methylene sequence distribution instead of conventional triad sequence distribution. To obtain a reliable model, parameter estimation with experimental data is first conducted. The SLD model along with the estimated kinetic parameters can be used to predict unmeasurable sequence length fraction. For the experimental conditions studied, the average methylene sequence length is predicted to change from 10 to 4 units as the propylene/ethylene mole feed ratio increases from 1.1 to 3.4.