Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene,propylene homopolymerizations,and their copolymerization

A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)₂ZrCl₂/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C^*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C^*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C^*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C^*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C^*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (k_p) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 867–875     

Kinetic elucidation of comonomer‐induced chemical and physical activation in heterogeneous ziegler‐natta propylene polymerization

We have kinetically elucidated the origins of activity enhancement because of the addition of comonomer in Ziegler‐Natta propylene polymerization, using stopped‐flow and continuously purged polymerization. Stopped‐flow polymerization (with the polymerization time of 0.1–0.2 s) enabled us to neglect contributions of physical phenomena to the activity, such as catalyst fragmentation and reagent diffusion through produced polymer. The propagation rate constant k_p and active‐site concentration [C*] were compared between homopolymerization and copolymerization in the absence of physical effects. k_p for propylene was increased by 30% because of the addition of a small amount of ethylene, whereas [C*] was constant. On the contrary, both k_p (for propylene) and [C*] remained unchanged by the addition of 1‐hexene. Thus, only ethylene could chemically activate propylene polymerization. However, continuously purged polymerization for 30 s resulted in much more significant activation by the addition of comonomer, clearly indicating that the activation phenomenon mainly arises from the physical effects. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Olefin terpolymerizations. II. 4-vinylcyclohexene and cyclooctadiene

4-Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis (1-η⁵-indenyl) zir-conium dichloride ( 1 ) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh-exane and cyclohexene were compared. The parameter K_πκ_p, which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two-fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc.     

Ene reactions of olefins. I. The addition of ethylene to 2-butene and the decomposition of 3-methylpentene-1

The pyrolysis of ethylene–butene-2 mixtures has been studied in a static system over the temperature range of 689°-754°k and for initial pressures of each olefin of 20–200 torr. The two main addition products were cyclopentene and 3-methylpentene-1. Kinetic evidence indicated that cyclopentene was formed from radical processes while 3-methylpentene-1 was formed by the molecular “ene¨?” addition of ethylene to butene-2 through a six-center transition state. The following rate constants were obtained: The pyrolysis of 3-methylpentene-1 has been studied over the same temperature range and for initial pressures of 20–100 torr. Kinetic evidence showed that the products ethylene and butenes were formed in both radical and molecular processes. Estimates of the rate constant k_?1t and k_?1c were, however, in reasonable agreement with the measurements of k_1t and k_1c. The mechanism of the ene reaction is discussed, and it is concluded that the transition state does not involve the formation of a biradical.     

C2‐symmetry dimethylated zirconocenes activated with triisobutyl aluminum as effective homogeneous catalysts for copolymerization of olefins

We investigated the catalytic performance of both bridged unsubstituted [rac‐EtInd₂ZrMe₂, rac‐Me₂SiInd₂ZrMe₂] and 2‐substituted [rac‐Et(2‐MeInd)₂ZrMe₂), rac‐Me₂Si(2‐MeInd)₂ZrMe₂] dimethylbisindenylzirconocenes activated with triisobutyl aluminum (TIBA) as a single activator in (a) homopolymerizations of ethylene and propylene, (b) copolymerization of ethylene with propylene and hexene‐1, and (c) copolymerization of propylene with hexene‐1 (at Al_TIBA/Zr = 100‐300 mol/mol). Unsubstituted catalysts were inactive in homopolymerizations of ethylene and propylene and copolymerization of propylene with hexene‐1 but exhibited high activity in copolymerizations of ethylene with propylene and hexene‐1. 2‐Substituted zirconocenes activated with TIBA were active in homopolymerizations of ethylene and propylene and exhibited high activity in copolymerization of ethylene with propylene and hexene‐1, and in copolymerization of propylene with hexene‐1. Comparative microstructural analysis of ethylene‐propylene copolymers prepared over rac‐Me₂SiInd₂ZrMe₂ activated with TIBA or Me₂NHPhB(C₆F₅)₄ has shown that the copolymers formed upon activation with TIBA are statistical in nature with some tendency to alternation, whereas those with borate activated system show a tendency to formation of comonomer blocks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2934–2941, 2010     

Mechanism and kinetics of polymerization of propylene in a microwave plasma

Flowing microwave plasma of propylene and propylene with argon was studied by mass spectrometry. Plasma composition was investigated as a function of external parameters such as pressure, argon/propylene ratio, and microwave-induced power. It was found that the propylene broke down to C₂H₂ and CH₄, or reacted further with propylene. Two main products, leading to the determination of three main chain reactions for the polymerization of propylene by ion-molecule interactions, were observed, namely, C₂H₂ and CH₄. These were the propylene, acetylene, and ethylene chain reactions. It was also found that the propylene disappeared in a pseudo-first-order reaction. Consequently an overall rate constant for the polymerization was determined (50 sec^–1 at 1 torr pressure for propylene plasma). This constant is found to be linearly dependent upon the propylene percent concentration, and nonlinearly dependent upon plasma pressure.Partly presented at the 157th meeting of the Electrochemical Society, St. Louis, Missouri, May 11–16, 1980.     

Stationary Kinetics of Light Olefin Oxidation by Hydrogen Peroxide in Aqueous Alkali Solutions in the Presence of Fe(III) Oxide

The steady-state kinetics of ethylene and propylene oxidation by hydrogen peroxide in the presence of Fe(III) oxide in aqueous solutions with the permanent adding of H₂O₂ to the reaction medium was studied. The use of an original method for the study of the steady-state reaction kinetics with gas chromatographic detection of substrate consumption from the gas phase made it possible to estimate the apparent rate constants of ethylene oxidation, the ratio of the rate constants of propylene and ethylene oxidation, the reaction orders with respect to the substrate and oxidant concentration, the dependence of the apparent rate constant of ethylene oxidation on the catalyst weight and on the pH of solution, and the apparent activation energy of the process under condition of substrate distribution between the gas and liquid phases. It was found that the kinetic isotope effect in ethylene oxidation is almost absent when completely deuterated ethylene is used.     

Dielectric properties of oligomers. VII. Low-molecular-weight propylene glycols

The dielectric properties of low-molecular-weight propylene glycols HO? [CH(CH₃)CH₂O]_n? H (n = 3, 4, 5) were investigated to clarify the effect of chain length on the dielectric properties. The measurement of dielectric constant and dielectric loss was carried out over the frequency range 30 Hz to 30 MHz at temperatures of ?20 to ?65°C. The static dielectric constants of these glycols are between 10 and 30, slightly smaller than values for the corresponding ethylene glycols of the same degree of polymerization. All of the Cole–Cole arcs, even that for pentapropylene glycol, can be represented by the empirical Davidson–Cole equation. The dielectric properties of homologous propylene glycols are compared with those for the ethylene glycols and are discussed in terms of the effects of chain length and intermolecular hydrogen bonds.     

Kinetics and mechanisms of the gas-phase reactions of the NO3 radical with aromatic compounds

The kinetics and nitrated products of the gas-phase reactions of the NO₃ radical with methoxybenzene, 1,2-, 1,3-, and 1,4-dimethoxybenzene, dibenzofuran and dibenzo-p-dioxin have been investigated at 297 ± 2 K and in the presence of one atmosphere of air. A relative rate method was used for the kinetic measurements. No reactions of methoxybenzene or dibenzofuran with the NO₃ radical were observed. The dimethoxybenzenes were observed to react by H-atom abstraction and NO₃ radical addition to the aromatic ring, while dibenzo-p-dioxin reacted by NO₃ radical addition to the aromatic rings. For these compounds, the NO₃ radical addition pathways were observed to be reversible. At the NO₂ concentrations employed, the NO₃-aromatic adducts reacted with NO₂ and the observed rate constants increased with increasing NO₂ concentration. However, for dibenzo-p-dioxin the observed rate constant became independent of the NO₂ concentration for concentrations ≥ 4.8 × 10¹³ molecule cm^?3, and under these conditions the rate constant of 6.8 × 10^?14 cm³ molecule^?1 s^?1 was taken to be that for addition of the NO₃ radical to the aromatic rings. The proposed NO₃ radical reaction mechanisms are discussed. © 1994 John Wiley & Sons, Inc.     

Time-resolved mass spectrometric study of the reaction H + Trans-2-Butene

The title reaction was studied in a discharge flow system using mass flow and modulated molecular beam sampling with phase-sensitive detection in order to obtain time-resolved mass spectrometric analysis. At total conversion exceeding 30%, the major products are methane and ethane when initially hydrogen atoms are in excess; when butene is in excess, the major products are ethane and propylene. No hydrocarbons with more than 4 carbon atoms were detected in the products. The reaction is a complicated one since the simplest reaction scheme that successfully simulates the experimental results comprises 20 elementary reactions. The simulation, coupled with sensitivity analysis, shows that with hydrogen atoms in excess, significant amounts of propylene formed in the initial decomposition of the butyl radical react further with hydrogen atoms to form methane and ethane. When butene is in excess, approximately [C₃H₆] ≈ [CH₄] + ½[C₂H₆] which means that this propylene does not react further and almost all methyl radicals end up as CH₄ or C₂H₆. At small conversion, simulation shows that the major product by far is propylene regardless of the [H]/[butene] ratio. The absence of higher hydrocarbons in the products is at variance with earlier results of Rabinovitch and coworkers; however the present work leads to a comparable value for the average rate constant ??_a = ωD/S where D and S is the amount of products arising from the decomposition and stabilization, respectively, of the butyl radical and ω is the collision frequency.     

Synthesis of bromine-functionalized polyolefins by scandium-catalyzed copolymerization of 10-bromo-1-decene with ethylene,propylene, and dienes

By use of a THF-containing trimethylsilylmethyl scandium catalyst system (C₅Me₄SiMe₃)Sc(CH₂SiMe₃)₂(THF)/[Ph₃C][B(C₆F₅)₄], the multi-component copolymerization of 10-bromo-1-decene (BrDC) with ethylene, propylene, and dienes has been achieved to afford a new family of bromine-functionalized polyolefins with controllable composition and high molecular weight. The copolymerization of BrDC with ethylene afforded the well-defined BrDC–ethylene copolymers with high BrDC incorporation (up to 12 mol%) and high molecular weight (M_w > 100 kg mol⁻¹). The terpolymerization of propylene, ethylene with BrDC afforded random ethylene–propylene–BrDC terpolymers with controllable bromine content (2 ~ 11 mol%), high molecular weight (M_w > 100 kg mol⁻¹) and low glass transition temperature (T_g = −51 °C ~ −67 °C). Moreover, the tetrapolymerization of ethylene, propylene, BrDC, and ethylidene norbornene or conjugated dienes such as isoprene and myrcene has been achieved for the first time to afford selectively the bromine-functionalized ethylene–propylene–diene rubbers containing various types of double bonds.     

POLYMERIZATION OF ETHYLENE AND PROPYLENE WITH VCL4-BUTYLLITHIUM CATALYSTS

Polymerization of ethylene and propylene with VCl₄-BuLi (Bu = n-Bu, sec-Bu, tert-Bu) catalysts was investigated. The VCl₄-BuLi catalysts were found to initiate the polymerization of ethylene and propylene. The VCl₄-BuLi catalysts gave an ultra high molecular polyethylene. The effect of the Li /V mole ratio on the polymerization of ethylene with the VCl₄-BuLi catalysts was observed, an the catalyst gave an optimum rate at the Li/V ratio of about 3.0. The polyethylene obtained with the VCl₄-BuLi catalyst was found to be a linear structure. In the polymerization of propylene with the VCl₄-BuLi catalyst, the polymers contain mm contents of 56–66% were produced.     

Supported catalysts for stereospecific polymerization of propylene

Tetrabenzyltitanium (B₄Ti), tribenzyltitanium chloride (B₃TiCl), tetra(p-methylbenzyl)titanium (R₄Ti) and tri(p-methylbenzyl)titanium chloride (R₃TiCl) have been used as catalysts for ethylene and propylene polymerization activated by AlEt₂Cl. B₄Ti-AIEt₂Cl in solution polymerizes ethylene readily but its activity decays rapidly. B₄Ti was also supported on Cab-O-Sil, Alon C, and Mg(OH)Cl. The last support was found to give catalyst with longest lifetime with a rate of polymerization, R_p = 7.0 g/hr-mmole Ti-atm ethylene. ¹⁴CO counting techniques gave 1.13 × 10^?3 mole of propagating center per mole of B₄Ti; the rate constant of propagation, k_p = 540 l./mole-sec. None of the tetravalent titanium compounds polymerize propylene in solution. However, when supported on Mg(OH)Cl, Cab-O-Sil, Alon C, Cab-O-Ti, and charcoal, they all polymerize propylene. In this work the supports were characterized by various techniques, including the paramagnetic probe method, to determine the concentration and nature of surface hydroxyls. Those factors controlling the rate and stereospecificity of propylene polymerization were investigated. The system B₃TiCl–Mg(OH)Cl–AlEt₂Cl is the most active with R_p = 2.89 g/hr-mmole Ti-atm propylene. The concentration of propagation center is 0.9 × 10^?3 mole per mole of B₃TiCl; k_p = 32 l./mole-sec. This catalyst gave only about 70% stereoregular polymer. Diethyl ether is found to raise stereospecificity to 100%, but there is a concommittent tenfold decrease of activity. Other interesting catalyst systems are: (π-C₅H₅)TiMe₃–Mg(OH)Cl–AlEt₂Cl (1.56, 89.5); (π-C₅H₅)TiMe₂–Mg(OH)Cl–AlEt₂Cl (0.075, 94.5); and (π-C₅H₅)TiMe₃–Alon C–Al-Et₂Cl (0.08,97.2), where the first number in the parenthesis is R_p in g/mmole Ti-hr-atm and the second entry corresponds to percentage yield of stereoregular polypropylene. Hafnocene and titanocene supported on Mg(OH)Cl produce only oligomers of propylene.     

Silolene-Bridged zirconocenium polymerization catalysts

A new silolene-bridged compound, racemic (1,4-butanediyl) silylene-bis (1-η⁵-in-denyl) dichlorozirconium ( 1 ) was synthesized by reacting ZrCl₄ with C₄H₈Si (IndLi)₂ in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta-fluorophenyl) borate ( 2 ) to produce in situ the zirconocenium ion ( 1 ⁺). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (T_p = ?55°C), producing refluxing n-heptane insoluble isotactic poly(propylene) (i-PP) with a yield of 99.4%, T_m = 164.3°C, δH_f = 20.22 cal/g and M?_w = 350 000. It has catalytic activities of 10⁷?10⁸ g PP/(mol Zr · [C₃H₆] · h) in propylene polymerization at the T_p ranging from ?55°C to 70°C, and 10⁸ polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1 ⁺ decreases gradually as T_p approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1 ⁺ is more stereospecific than the analogous cation derived from rac-dimethylsilylenebis (1-η⁵-indenyl)dichlorozirconium ( 4 ). The variations of polymerization activities in ethylene and in propylene for T_p from ?55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium-propylene π-complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π-complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude r_E ? 4r_p. Furthermore, r_E.r_p ? 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo-selectivity than the corresponding 1 ⁺ or 4 ⁺ system. © 1994 John Wiley & Sons, Inc.     

Sequence distributions versus catalyst site behavior of in situ blends of polypropylene and poly(ethylene-co-propylene)

Sequential polymerizations of first propylene and then ethylene, propylene mixtures with the same Ziegler–Natta catalyst system produce in situ blends known as high-impact polypropylenes. Over 100 high-impact polypropylenes are characterized in terms of weight fractions and sequence distributions for isotactic polypropylene, atactic polypropylene, an amorphous ethylene propylene copolymer, and a crystalline ethylene propylene copolymer. The apparent r₁r₂ behaviors of the E/P copolymers suggest that the amorphous and crystalline E/P copolymers principally arise from different types of catalyst sites as opposed to originating strictly from compositional heterogeneities. The amorphous copolymers consistently have r₁r₂ values close to unity over a broad range of compositions, while the corresponding crystalline copolymers have apparent r₁r₂ values that range from 2 to over 20. An apparent r₁r₂ close to unity not only reflects random sequencing but also indicates a narrow compositional distribution. This r₁r₂ result indicates that the amorphous E/P copolymers are produced from a singular type of catalyst site. The higher r₁r₂ values shown by the crystalline E/P copolymers indicate broad compositional distributions that are produced by a different type or types of catalyst sites. The ratio of amorphous to crystalline ethylene, propylene copolymers is nominally around 80/20 over a broad range of impact copolymer compositions. The consistency of this result suggests that the two basic types of catalyst sites producing E/P copolymers are also in an approximate 80/20 ratio. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1527–1542, 1998     

Copolymerization of Ethylene and Propylene Using Silicon Tetrachloride‐Modified Silica/MAO with Et[Ind]2ZrCl2 Metallocene Catalyst

For the copolymerization of ethylene with propylene or a higher α‐olefin, using Et[Ind]₂ZrCl₂ metallocene catalyst, modification of silica with silicon tetrachloride prior to MAO adsorption can increase the activity, which is more pronounced for ethylene/1‐hexene copolymerization at higher pressure and temperature. The molecular weight of the copolymer produced was lower and the polydispersity tends to be decreased. No significant effect of SiCl₄ addition on the microstructure and the chemical composition distribution of the copolymer produced was observed.     

H2O2-photosensitized emulsion copolymerization of tetrafluoroethylene with propylene

The H₂O₂-photosensitized emulsion copolymerization of tetrafluoroethylene with propylene was carried out at room temperature in the presence of gaseous monomers of 50 mole-% tetrafluoroethylene content. The conversion increased almost linearly with irradiation time. The rate of polymerization was proportional to the 1.0 power of H₂O₂ concentration up to 3.5 × 10^?3M H₂O₂ and the 0.46 power of H₂O₂ concentration above 3.5 × 10^?3M H₂O₂. The result obtained at low H₂O₂ concentration was almost consistent with that obtained in the radiation-induced method. The rate of polymerization was proportional to the 0.58 power of the emulsifier concentration, and the degree of polymerization was independent of the emulsifier concentration. The H₂O₂-photosensitized emulsion copolymerization of tetrafluoroethylene with propylene is terminated mainly by degradative chain transfer of the propagating radical to propylene at low H₂O₂ concentration and by the reaction of the propagating radical with OH radical from photolysis of H₂O₂–aqueous solution at high H₂O₂ concentration.     

Polymer Blend for Electrolyte and Electrode Coatings

Summary: The thermal and morphological properties of PEO/copolyether electrolyte and carbon black composite have been studied. A copolyether poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) was used at 20 wt.-% in relation to PEO in order the improve the carbon black dispersion through interaction with the amino end capped function. The polymer matrix presented semicrystalline structure and the addition of LiClO₄ and carbon black decreases significantly the crystallinity of the system. Sub-micrometric dispersion of carbon black was observed. The conductivity results as a function of temperature exhibited a typical VTF behaviour for the electrolyte. Almost constant conductivities of 2 × 10⁻⁴ S · cm⁻¹ were observed for the composite with 5 wt.-% of carbon black, in the range of temperature between 35 and 95 °C, which indicates a significantly contribution of electronic conduction.     

Olefin copolymerization with metallocene catalysts. II. Kinetics,cocatalyst, and additives

The kinetics of ethylene/propylene copolymerization catalyzed by (ethylene bis (indeyl)-ZrCI₂/methylaluminoxane) has been investigated. Radiolabeling found about 80% of the Zr to be catalytically active. The estimates for rate constants at 50°C are k₁₁ = 1104 (M_s)^?1, k₁₂ = 430 (M_s)^?1, k₂₂ = 396 (M_s)^?1,k₂₁ = 1020 (M_s)^?1, and k^A_tr,1 + k^A_tr.2 = 1.9 × 10^?3 s^?1. Substitution of trimethylaluminum for methylaluminoxane resulted in proportionate decrease in polymerization rate. The molecular weight of the copolymer is slightly increased by loweing the [Al]/[Zr] ratio, or addition of Lewis base modifier but at the expense of lowered catalytic activity and increase in ethylene content in the copolymer. Lowering of the polymerization temperature to 0°C resulted in a doubling of molecular weight but suffered 10-fold reduction in polymerization activity and increase of ethylene in copolymer.     

Properties of ethylene–propylene–vinyl chloride graft copolymers. I. Viscoelasticity of ethylene–propylene copolymers

The viscoelastic behavior of two different ethylene–propylene copolymers was studied as a function of the molar ratios of the components and the distribution of the lengths of the ethylene and propylene sequences. The glass transition temperatures T_g agree with the values calculated from relations between T_g and component ratio established by other authors. The copolymer with longer ethylene and propylene sequences was found to exhibit a relaxation spectrum with a slope less steep than ?0.5. This broadening is explained by the broader distribution of friction factors of the statistical segments in this copolymer and by differences in crystallike nearest-neighbor packing.