Homogeneous Ziegler-Natta catalysis: Efficiency improvement of vanadium catalyst systems by tributyltin hydride for the ethylene/propylene/diene terpolymerization

The effect of tributylin hydride on different vanadium-based homogeneous catalytic systems for the ethylene/propylene/diene (EPD) terpolymerization was studied. Productivity improvements were always observed. Studied on the composition of the polymerization residues as well as on the interaction between single components of the catalytic system were also carried out. The results are interpreted on the basis of the enhanced oxidation of the vanadium(II) species by radical intermediates resulting from the reaction between tin hydrides and the chlorinated organic activator.     

Monomer-isomerization polymerization, 35. Kinetics of monomer-isomerization polymerization of 2-butene with Ziegler-Natta catalyst

The kinetics of monomer-isomerization polymerizations of cis-2-butene with TiCl₃/Al(C₂H₅)₃ catalysts in the presence and absence of NiCl, was studied. Both the rate of isomerization and polymerization increased as a function of the concentrations of the monomer and catalyst. The apparent activation energies for the polymerization with TiCl₃/Al(C₂H₅)₃ and with TiCl₃/NiCl₂/Al(C₂H₅)₃ were estimated to be 25,6 and 17,2 kJ/mol, respectively. This difference in the apparent activation energy for monomer-isomerization polymerization may be accounted for by the rates of isomerization to 1-butene. The reaction constants for the isomerization and polymerization were evaluated by simulation. The rate of polymerization with the TiCI₃/Al(C₂H₅)₃ catalyst was found to be about 40 times higher than that of isomerization, and in the presence of NiCl₂, both rates become similar. From product analysis produced with TiCl₃ and alkylaluminium compounds, it is concluded that the active sites for isomerization involve Ti²⁺ complexes and those for the polymerization involve Ti³⁺ complexes.     

Propene polymerization with a magnesium chloride-supported ziegler catalyst, 1. Principal kinetics

The main kinetic behavior of the slurry polymerization of propene with a MgCl₂-supported TiCl₄/C₆H₅COOC₂H₅ catalyst, activated by Al(C₂H₅)₃, was studied, Examination of the dependence of the polymerization rate on temperature and concentrations of Al(C₂H₅)₃ and of propene resulted in a Langmuir-Hinshelwood rate law with the number of polymerization centers dependent on time. The Polymerization rate as function of the polymerization temperature shows a maximum, which is compatible with the rate law. The analysis of the phenomenon of an optimum temperature gave 15 KJ. mol^?1 and 36 KJ. Mol ^?1 for the activation energy of the rate determining step and the adsorption energy of Al(C₂H₅)₃, respectively. Examination of the rapid decay of the polymerization rate showed that the main part of the decay is represented by a second order decay independent of the amount of polymer produced, which can be understood by a second order decay of surface sites by Al(C₂H₅)₃. The number of active centers of the catalyst in gas phase polymerization was estimated applying the inhibition method with carbon monoxide. The results show a constant value for the propagation rate constant, K_p, during the second order rate decay. The observed polymerization kinetics strongly suggest the existence of two kinds of polymerization centers (isotactic and atactic).     

On structure and temperature transformations of nascent polyethylene,produced by polymerization of ethylene in presence of a modified Ziegler-Natta catalyst

Nascent polyethylene with high molecular mass (M_n ≈ 10⁵, M_w ≈ 10⁶) produced in hydrocarbon medium in presence of TiCl₄/(C₂H₅)₂AlCl/(C₆H₅)₂Mg catalyst was studied by means of X-ray diffraction, electron and light microscopy, and low-angle light scattering. It consists of porous spherulite-fibril aggregates indicating a not very high degree of crystallinity α(α≈). Data, concerning the dependence of spherulite dimensions, degree of crystallinity and other structure parameters of nascent polyethylene on polymerization time and temperature are discussed. Using the same structure-analytical methods some samples of nascent polyethylene were studied after annealing them in nitrogen atmosphere at different temperatures between 110–250°C with successive cooling to room temperature. Furthermore both the endo- and exothermal transitions occurring in the nascent and annealed structures after heating to 250°C were studied by means of DTA and DSC. The experimental information leads to the conclusion that nascent polyethylene structures consist of crystalline folded chain lamellae with an increased amount of tie molecules between them as well as of extended chain crystals.     

Sequence and branching distribution of ethylene/1-butene copolymers prepared with a heterogeneous Ziegler catalyst

Ethylene/1-butene copolymers prepared with a heterogeneous titanium-based catalyst were separated into five fractions by successive solvent extraction, and the triad distributions of each fraction were determined by ¹³C NMR measurements. Conditional probabilities (P_EE, P_EB, P_BE, P_BB), reactivity ratios (r₁, r₂), and persistence ratio (p) of each fraction were calculated from the triad distributions observed. The analysis of these values suggests that the heterogeneous Ziegler catalyst has multiple active sites, and the copolymer has nearly a Bernoullian sequence distribution.     

Effect of the internal/external donor pair in high-yield catalysts for propylene polymerization, 2. Polymerization results

The behaviour in propylene polymerization of catalysts containing ethyl benzoate/methyl p-toluate (EB/MPT) or dibutyl phthalate/triethoxy(phenyl)silane (DBP/EPS) as internal/external donor pairs was investigated. Comparing catalyst composition with performance, it appears that no qualitative difference exists in the role of MPT and EPS, both acting as poisons of atactic sites and activators of isotactic sites. A higher efficiency of EPS is evident. On the contrary, a difference can be found between the internal donors EB and DBP/DBP seems not directly involved in the formation of isotactic centers as EB. These results, though obtained under conditions leading to much lower activities than usual for the catalysts considered, can be assumed to describe the general behaviour of the donor pairs investigated when the polymerization is carried out in the absence of hydrogen.     

TiCl4/MgH2-supported Ziegler-type catalyst system, 2. Effect of Ti concentration,Ti content and surface area of TiCl4/MgH2 catalyst on the concentration of active sites in ethylene polymerization

The determination of active centres concentration in ethylene polymerization using various TiCl₄/MgH₂-Al(C₂H₅)₃ catalytic systems, by the ¹⁴CO radio-tagging method, is reported. It is found that with increasing the absolute titanium amount the concentration of active centres, [C^*], increases, whereas the propagation rate constant, k_p, decreases. In addition, using various TiCl₄/MgH₂ catalysts in ethylene polymerization, it is found that the lower the Ti content, the higher is the surface area of the catalyst and the higher is the polymerization activity. Determination of [C^*] shows consclusively that the decrease in the polymerization activity observed to occur with increasing the Ti content, and thus decreasing the surface area, is unequivocally due to a reduction in the concentration of active centres but not to any fundamental change in the value of the propagation rate constant.     

Monomer-isomerization polymerization, 27. Monomer-isomerization in competition with polymerization of α-olefins with Ziegler-Natta catalysts

The monomer-isomerization was studied in the polymerization of α-olefins with the catalytic systems TiCl₃/(C₂H₅)₃Al and Ti(OC₄H₉)₄/(C₂H₅)₃Al. The isomerization to the corresponding olefins with internal double bond was found to occur during the polymerization. With the system TiCl₃/(C₂H₅)₃Al only a small amount of isomerized olefin was produced as result of the rapid polymerization of the α-olefins. Significant isomerization was observed to take place with a poor polymerization catalyst such as Ti(OC₄H₉)₄/(C₂H₅)₃Al. Isomerization and polymerization of α-olefins with Ziegler-Natta catalysts were found to depend on the oxidation state of titanium.     

On the anionic polymerization of dialkylaminoisoprenes, 4. Experimental observation of the unusual polymerization kinetics

The anionic polymerization of 5-(N,N-dialkylamino)isoprenes with sec-butyllithium was investigated in different solvents under various conditions. The homopolymerization can be described as a 2^nd order reaction with respect to the monomer concentration, indicating that two monomer units are involved in the rate determining reaction. A mechanistic proposal to explain this unusual behaviour is based on the structure of amino-functional lithium organic compounds.     

Studies on the polymerization of ethylene using a high-yield MgCl2-supported titanium catalyst, 1. Effects of synthesis parameters on catalyst activity and polymer properties

The preparation of a highly active Ti-Mg catalyst in two steps is reported. the first step is a Grignard reaction conducted in hexane with an under-stoichiometric amount of tetrahydrofuran. In the second step the Grignard suspension is treated with a TiCl₄/CCl₄ mixture. Owing to optimized synthesis conditions after a thermal activation the catalyst suspension is ready for use in combination with an alkylaluminium cocatalyst without further separation and drying operations. Because of its high response to H₂ the catalyst may preferably be used for the production of polyethylene (PE) for injection moulding. Depending on the Ti content the catalyst shows an activity of between 184 and 250 kg PE per g Ti per h and per bar for a PE with melt flow index between 20 and 30 g/10 min. The content of Ti⁴⁺ in the catalyst is high (up to 72 wt.-%). The catalyst suspension shows a marked resistance against reduction by the cocatalyst. The catalytic activity not only depends on the mole ratio of the individual catalyst components but even more on their actual concentration in the reaction medium.     

Effect of the internal/external donor pair in high-yield catalysts for propylene polymerization, 1. Catalyst-cocatalyst interactions

The chemistry of the catalyst-cocatalyst interaction was investigated in systems containing different internal/external donor pairs. Qualitatively similar results were obtained with the ethyl benzoate/methyl p-toluate (EB/MPT) and dibutyl phthalate/triethoxy(phenyl)silane (DBP/EPS) systems, which thus were assumed to follow the same model. Quantitative differences were accounted for by assuming a different basic strength of the two donor pairs towards MgCl₂ and AlEt₃.     

A systematic approach to the study of multicomponent polymerization kinetics: the butyl acrylate/methyl methacrylate/vinyl acetate example, 2. Bulk (and solution) terpolymerization

A systematic study of the terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate (BA/MMA/VAc) is being conducted. In the second stage of this study, bulk (and solution) terpolymerizations of BA/MMA/VAc were performed. The polymers produced were characterized for conversion, composition and molecular weight. The terpolymerizations exhibited behaviour similar to vinyl acetate-containing copolymerizations, that is, a “double gel effect” was observed. During the first period of the reaction the acrylic monomers virtually “copolymerized” and thus the reaction exhibited the characteristics of a “solution” copolymerization of the acrylic monomers with the vinyl acetate acting as the “solvent”. Typical “solution” polymerization behaviour, i. e., a dampened autoacceleration or gel effect, was in evidence for this first period of the reaction. After the virtual deplection of the acrylic monomers, the remaining vinyl acetate polymerized and exhibited its own characteristic gel effect. Estimates of the copolymerization reactivity ratios obtained previously were found to accurately predict terpolymer composition up to high conversion levels. Molecular weight results indicated that branched polymers were being produced at high conversions in the bulk experiments.     

The polymerization,copolymerization and terpolymerization of 1-isopropylidene-3a.4.7.7a-tetrahydroindene by anionic coordinate,radical and anionic catalysts

By means of vanadium based anionic coordinate catalysts 1-isopropylidene-3a.4.7.7a-tetrahydroindene (I) can be terpolymerized with ethylene and propylene and copolymerized with ethylene. IR, NMR, UV spectroscopic data, and mol. wt. distributions are reported for the polymers. The incorporation of I is predominantly by opening of the cyclohexene double bond. The content of I was generally less than 10 mole-%. Attempts to obtain homopolymers of I and copolymers of propylene and I with this type of catalyst were unsuccessfull. No solid polymer could be produced from I by free radical or anionic catalysts. With AIBN only oligomers were obtained which had cyanoisobutyric groups attached to the conjugated double bond system. K or KNH₂ in ammonia solution react with I in equimolar ratios to give waxy products which do not contain NH₂ groups. With K di-hydrogenated derivatives of I are formed. The results have been interpreted in terms of stabilized radicals and anions derived from I which are unable to propagate.     

TiCl4/MgH2-supported Ziegler-type catalyst system, 3. New findings on the concentration of active sites in ethylene/1-hexene copolymerization

The effect of 1-hexene on the rate constant of ethylene polymerization and on the number of active centres in the copolymerization of ethylene with 1-hexene is reported. Using three TiCl₄/MgH₂? Al(C₂H₅)₃ catalysts, of different Ti contents and surface area in the polymerization reveals that the addition of small amounts of the comonomer 1-hexene results in a two- to three-fold increase in the rate of ethylene consumption when a low-Ti-content catalyst is used. In contrast, no fundamental change in the catalytic activity was observed when a high-Ti-content catalyst is employed. The determination of the concentration of active centres C* by means of the ¹⁴CO radio-labelling technique, shows that C* in ethylene/1-hexene copolymerization is more or less the same as in ethylene homopolymerization.     

Propene polymerization with Mg(OEt)2-supported TiCl4 catalyst, 1. Catalyst composition and behavior

Catalysts obtained from TiCl₄ and ball-milled Mg(OEt)₂ in the presence of a halide compound (dichloroethane, chlorobenzene or dichlorobenzene) and/or an internal donor (ethyl benzoate or diisobutyl phthalate) were prepared for propene polymerization. The composition of the catalysts was analyzed by IR, GC, atomic absorption spectroscopy and titration. The exchange reaction between the ethoxy group of the support and the chloride group of TiCl₄ was found to depend profoundly on the halide compound and/or the internal donor used. The propene polymerizations were carried out using various Mg(OEt)₂-supported catalysts and triethylaluminium as cocatalyst with or without external donor (triethoxyphenylsilane). The catalyst activity and stereospecificity were examined.     

Influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(Me4Cp)(N-tert-butyl)TiCl2/methylaluminoxane Ziegler-Natta catalysts

Styrene was copolymerized with ethylene using Me₂Si(Me₄Cp)(N-tert-butyl)TiCl₂/methylaluminoxane (Me = methyl, Cp = cyclopentadienyl) varying monomer concentration, styrene/ethylene molar ratio and polymerization temperature. Increasing styrene or decreasing ethylene concentration, respectively, in the monomer feed lowered both activity of the catalyst system and molecular weight of the copolymer. Only at low styrene content, a linear correlation of styrene concentration in the monomer feed and styrene incorporation in the copolymer was found. From copolymerizations at various temperatures the activation energy of the insertion step was calculated to be 56 kJ/mol. According to Fineman-Ross plot, the copolymerization parameters are r_E = 23,4 for ethylene and r_S = 0,015 for styrene. Investigation of the thermal properties by means of differential scanning calorimetry and dynamic mechanical analysis revealed pronounced decrease of melting temperature and increase of glass transition temperature with increasing styrene content.     

Studies on the polymerization of ethylene using a high-yield MgCl2-supported titanium catalyst, 2. Kinetic studies

Polymerization of ethylene was carried out in a batch process under pressure with an optimized high-yield Ti/Mg-catalyst. It was shown through gas chromatography analysis as well as by educt/product mass balances that no side-reactions take place, and therefore, the monomer is quantitatively converted to polyethylene. It is demonstrated that influences of diffusion are excluded under the described experimental condition. The dependence of the overall polymerization rate on time shows that the rate at constant pressure is constant from the beginning over a certain period of time. The rate of polymerization under isobaric as well as isochoric conditions was determined to be first order with respect to monomer concentration and catalyst concentration. The overall activation energy obtained for this catalytic system was determined to be 32 kJ · mol^?1.     

TiCl4/MgH2-supported Ziegler-type catalyst system, 1. Determination of active centres

Determination of active centres using TiCl₄/MgH₂-supported catalyst system in ethylene polymerization is reported. A radio-tagging technique, whereby ¹⁴CO is used to label the polymerization active centres, is employed. Optimization of the ¹⁴CO/Ti ratio showed that the polymer radioactivity remained constant after a ¹⁴CO/Ti ratio of about 8 was attained. At the optimal ¹⁴CO/Ti ratio, it is found that up to 14% of the titanium on the catalyst surface are active in polymerizations at 40°C, 10 min reaction time, and 30 min contact time period of ¹⁴CO with the polymerization medium. Moreover, the value of the corresponding propagation rate constant, K_p, was found to be about 230 dm³/(mol·s).     

Determination of the number of active centers in Ziegler-Natta polymerization of propene using sulfur-containing terminating agents, 1. Application of carbon disulfide

Polymerization of propene catalyzed with TiCl₃ · 1/3(AlCl₃)/AlEt₂Cl or TiCl₃ · 1/3(AlCl₃)/AlEt₃ systems in heptane at 323,2 K in the presence of CS₂ was studied. It was demonstrated that the sharp decrease of rate, observed upon addition of CS₂, is not due to a decrease of the organometal concentration, although some consumption of the organometal was evidenced by means of IR measurement. Tagging of the growing chains was monitored by determination of the sulfur content in the polymer. Side reactions of CS₂, leading to a blank content of sulfur in polypropylene, were observed in the presence of catalytical components even after their deactivation. Thus, a thorough washing of the polymer was necessary. A substantial increase of heptane solubles observed upon addition of larger amounts of CS₂ was found to be due to a much lower molecular weight of the polymer, while stereospecificity of the catalytical system was virtually preserved. It was concluded that CS₂ behaves as a suitable terminating and tagging agent.