Polymerization of styrene with the VOCl3/Li(iC5H11) catalyst system

The polymerization of styrene with the VOCl₃/Li(iC₅H₁₁) catalyst system has been studied. Rates of polymerization fall sharply with increase in Li/V ratio; the molecular weights, however, show a maximum at Li/V = 1. Polymerization is first order with respect to catlyst as well as monomer concentrations. Activation energy was found to be 5.67 kcal/mole. Zinc diethyl acts as chain transfer agent. There was no effect of trans-stilbene on molecular weights as well as on rate of polymerization. Valence of vanadium at Li/V molar ratio 1 is 4.12 and it decreases with increase in ratio.     

The initiation mechanism of polymerization by the system AlEt3/H2O

The reaction between H₂O and triethylaluminum Al(Et₃) as well as the initiation mechanism of the polymerization by the system AlEt₃/H₂O have been examined by means of tritiated water, Considerable amount of tritium from tritiated water remained in the system AlEt₃/H₂O prepared at room temperature. Heat treatment of the system causes both the extensive decrease of tritium content and loss of catalyst activity. Polymers of styrene and isobutyl vinyl ether prepared by the system AlEt₃/H₂O were found to be radioactive. These findings have been taken to assume that acid hydrogen does exist in the system AlEt₃/H₂O and is directly responsible for the initiation of cationic polymerization.     

Ethylene polymerization on a high activity supported catalyst: MgCl2 (THF)2/TiCl4/AlEt2Cl

A magnesium/electron donor complex was used as support for the synthesis of a titanium catalyst. By interaction of TiCl₄ with MgCl₂(THF)₂ a highly active and stable catalyst for ethylene polymerization was obtained. The catalytic activity of the MgCl₂(THF)₂/TiCl₄/AlEt₂Cl system in the polymerization of ethylene was investigated as a function of Mg/Ti and Al/Ti mole ratios as well as the donor concentration in the system. Some kinetic studies of ethylene polymerization in the presence of this catalyst allowed us to determine the concentration of active centres (ca. 60 mol-% of Ti), rate constants of elementary reactions (k_p ≈ 92 dm³/(mol · s)) and kinetic equations. From these results it was possible to find further evidence for the role of the donor ligands in titanium catalysts supported on magnesium dichloride in the presence of Al-alkyls as cocatalysts.     

Kinetics of polymerization of 1,3-dioxepane with the Al(C2H5)3/H2O catalyst system

The kinetics of the polymerization of 1,3-dioxepane (DH) with the catalytic system Al(C₂H₅)₃/H₂O was studied. The dependence of the polymerization rate R₀ of the monomer DH(M) may be represented by the equation: The kinetic scheme which verifies the obtained results is that which takes into consideration in the starting period of the polymerization the existence of chain transfer to the monomer. The decrease of the polymerization rate and the diminishing of the intrinsic viscosity at high conversions points to the existence of chain transfer to the polymer in this stage of the reaction. The reaction rate constants of the chain transfer to the monomer are one order of magnitude higher than those of the transfer reaction to the polymer.     

Stereospecific polymerization of higher α-olefins with the solvay type catalyst TiCl3/Cp2Ti(CH3)2

Polymerizations of higher α-olefins (C₁₀–C₂₀) were carried out at 40°C in heptane, using the following three catalysts which differ in the isospecificity for propene polymerization: Solvay type TiCl₃/Cp₂TiMe₂((A) highly isospecific), Solvay type TiCl₃/AlEt₃((B) isospecific) and TiCl₃.3Py/MgCl₂/AlEt₃((C) aspecific). The isospecificity of the catalysts was found to decrease in the following order: (A) ? (B) ? (C), which agrees well with the results obtained in propene polymerization. The crystallinity of these polymers is discussed in brief.     

Kinetics of deactivation in the BuOTiCl3/AlEt2Cl initiated polymerization of styrene

The deactivation of the catalytic activity of the BuOTiCl₃/AlEt₂Cl initiated polymerization of styrene in heptane was found to follow a second-order rate law. The varying slopes in the second-order plots observed with varying catalyst concentrations are due to the heterogeneous nature of these colloidally dispersed catalysts. Site poisoning by reversible adsorption of the AlEtCl₂ formed, is proposed as the probable reason for the deactivation.     

Adsorption of propylene and allene on TiCl3·1/3 AlCl3 and polymerization of allene with the system TiCl3·1/3 AlCl3/AlEt2Cl

Adsorption of propylene and allene from the gas phase on TiCl₃·1/3 AlCl₃ and TiCl₃·1/3 AlCl₃/AlEt₂Cl catalyst was measured volumetrically. In the ranges of 296–334 K and 1–100 kPa, the adsorbed amounts of both gases was found to be approximately proportional to the gas pressure. The adsorbed amount of allene is about twice as high as that of propylene under the same conditions. Low heats of adsorption of both propylene and allene support the assumption of the physical nature of the adsorption. Addition of AlEt₂Cl to the TiCl₃·1/3 AlCl₃ catalyst did not change substantially the sorption properties of the catalyst. Polymerization of allene with the system TiCl₃·1/3 AlCl₃/AlEt₂Cl in heptane was found to be first order in monomer and the rate decreases with increasing yield. A mechanism of retardation by the polymer formed is probably operative. Both heptane-soluble and heptane-insoluble polyallenes are produced. The soluble polymer has M?_n ≈ 10³ and a very narrow molecular weight distribution (M?_w/M?_n = 1,2 ± 0,2). Polyallene comprises mainly vinylidene units.     

Ethene polymerization with a poly(styrene-co-divinylbenzene) beads supported rac-Ph2Si(Ind)2ZrCl2 catalyst

Poly(styrene-co-divinylbenzene) beads supported rac-Ph₂Si(Ind)₂ZrCl₂ was prepared and tested as a catalyst for ethene polymerization using methylaluminoxane (MAO) as a cocatalyst. At a polymerization temperature below 100°C, the catalyst showed pretty high activity to give polyethene beads replicating the shape of the carrier. With increasing polymerization temperature up to 150°C, the catalyst activity increased drastically but the spherical shape of polyethene disappeared due to the melting. From the plots of apparent activity against polymerization temperature, it was suggested that the polymerization below 100°C is more or less controlled by monomer diffusion through the crystalline polyethene films.     

Polymerization of methyl methacrylate with V(acac)3 and VOCl3 in combination with methylaluminoxane

The polymerization of methyl methacrylate (MMA) with V(acac)₃ and VOCl₃ in combination with methylaluminoxane (MAO) was investigated. The obtained polymers have a relatively narrow molecular weight distribution (M?_w/M?_n < 1,5). It was found that the isotactic triad content of the polymers increases with increasing temperature and MAO/V and MAO/MMA mole ratios. The interaction between MMA and MAO has an influence on the tacticity of radically (initiator AIBN) obtained polymers: in presence of MAO the fraction of isotactic triads (mm) is higher. The catalytic activity of MAO-containing catalysts (V(acac)₃/MAO and VOCl₃/MAO) was compared with that of AlEt₃-containing catalysts (V(acac)₃/AlEt₃ and VOCl₃/AlEt₃). It was not much different, but for MAO as cocatalyst the isotacticity of the resulting PMMA's was higher, and the polydispersity lower, than with AlEt₃ as cocatalyst.     

13C NMR study of the tacticity of poly(propylene oxide)s prepared by polymerization with α,β,γ,δ-tetraphenylporphyrin/AlEt2Cl as initiator system: An example of first-order markovian statistics in ring-opening polymerization

Racemic and enantiomerically enriched poly(propylene oxide)s were prepared using α, β, γ, δ-tetraphenylporphyrin/AlEt₂Cl as initiator system. Triad tacticity of the polymers was analyzed by ¹³C NMR spectroscopy (62,89 MHz). A predominance of isotactic triads was observed in the case of the racemic polymer, corresponding to a non-random distribution of configurational units in the polymer chain. A model correlating tacticity with enantiomeric excess of starting monomer in the case of a first-order Markovian distribution was established. Good agreement between experimental results and calculated triad contents (according to the model previously described) was observed for enantiomerically enriched polymers. This indicates a steric control by the last unit of the growing chain end. The influence of the size of the substituent was examined for the case of poly(1,2-epoxybutane). The origin of the chain-end effect is discussed.     

Monomer-isomerization polymerization, 37. Effect of transition metal chlorides on monomer-isomerization polymerization of 2-butene with TiCl3/Al(C2H5)3 as catalyst

The effect of transition metal chlorides (MtCl_x) as isomerization catalysts was examined in the monomer-isomerization polymerization of cis-2-butene with TiCl₃/Al(C₂H₅)₃ as a catalyst. The isomerization and polymerization depend on both, MtCl_x and MtCl_x/TiCl₃ mole ratio. The rate of polymerization of 2-butene with TiCl₃/Al(C₂H₅)₃/MtCl_x (mole ratio Al/Ti = 3,0, Mt/Ti = 1,0) as catalysts decreases in the following order: NiCl₂ > CoCl₂ > FeCl₃ > None > MnCl₂ > CrCl₃. This order was found to be in a good agreement with the electronegativity of the metal atom in the chloride.     

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.     

Cationic polymerization of α-pinene with the binary catalyst AlCl3/SbCl3

Oligomers of α-pinene ( 1 ) with relatively high molecular weight (number-average molecular weight M _n = 1140, weight-average molecular weight M _w = 2590) were obtained with the binary catalyst AlCl₃/SbCl₃ in toluene at ? 15°C ([AlCl₃]₀ = 42,5 mmol · L^?1, mole ratio SbCl₃/AlCl₃ = 0,50). The yield was higher than 90%, and the dimer content was as low as 5 wt.-%. In contrast, AlCl₃ alone gave predominantly dimers and lower oligomers in poor yield, whereas SbCl₃ had no catalytic activity for 1. ¹H NMR analysis reveled that the structure of the higher-molecular-weight fraction (M _n = 2920, M _w = 3690) of the oligomers obtained with AlCl₃/SbCl₃ is 6 , which consists of a cyclohexene ring with an endo-olefin group, most likely derived from the cationic monomer isomerization of α-pinene via the ring-opening of the cyclobutane unit. Effects of the reaction conditions on the polymerization rate and molecular weight were also investigated.     

Oligomerization of 1-hexene initiated by Zr(OnPr)4-AlEt2Cl, 2. Mechanistic aspects

The mechanistic aspects of 1-hexene oligomerization, initiated by Zr(OnPr)₄-AlEt₂Cl at 20°C, are discussed on the basis of the product structures and distributions, the stability and reactivity of Mt-alkyls (Mt = metal) formed during 1-hexene oligomerization, the reaction behaviour of an internal olefin (cis-2-hexene) and the investigation of interactions between Zr (OnPr)₄-AlEt₂Cl. After comparing the different possible initation routes for 1-hexene oligomerization, a mechanism via insertion of 1-hexene into Al-alkyl bonds activated by zirconium is proposed. It was found that the olefin addition is not regiospecific. Primary addition into a linear alkyl-metal bond leads to an olefin insertion, whereas secondary addition only leads to elimination; when α- or β- branched alkyl-metal bonds are involved, only transfer to monomer takes place.     

Propene polymerization with δ-TiCl3/AlCl(C2H5)2 and δ-TiCl3/Al(C2H5)3 catalyst systems, 1. Effect of external donors

The effect of ethyl benzoate (EB), diisobutyl phthalate (DIBP), dibutyl ether (DBE) and triethoxy(phenyl)silane (EPS) as third components on the propene polymerization with the catalyst systems δ-TiCl₃/AlCl(C₂H₅)₂ and δ-TiCl₃/Al(C₂H₅)₃ was investigated. The influence of external donors on the isotacticity, catalyst activity and average molecular weight (M _v) was tested. If external donors are employed, M _v decreases, the insoluble fraction in boiling isooctane increases and the catalyst activity is strongly influenced by the mole ratio external donor/TiCl₃. The results indicate that all external donors employed have the same qualitative effect on catalytic active centers.     

Copolymerization of ethylene with 1-hexene and 1-octene: correlation between type of catalyst and comonomer incorporated

The behaviour of catalytic systems based on zirconium compounds for the copolymerization of ethylene with 1-hexene and 1-octene is reported. The metallocenes (CH₃)₂SiCp₂ZrCl₂, Cp₂ZrCl₂ (Cp = η⁵-cyclopentadienyl), C₂H₄[Ind]₂ZrCl₂ and (Ind = η⁵-indenyl) were chosen for this study. The bridged catalysts, (CH₃)₂SiCp₂ZrCl₂ and C₂H₄[Ind]₂ZrCl₂, and the metallocene Cp₂ZrCl₂ showed similar catalytic activities for home- and copolymerization of ethylene with 1-hexene. ¹³C NMR analysis showed that the composition of copolymerization products depends on the catalytic system, in other words, on the ligand structure of the transition metal. Copolymers obtained using the bridged catalysts have greater incorporation of comonomer. Thermal analysis and viscosity measurements demonstrated that an increase of the comonomer concentration reduces the melting point, the crystallinity and the molecular weight of the copolymer. Results from infrared spectroscopy showed that β-elimination is one of the possible termination reactions. The monomer reactivity ratios r were determined for all catalytic systems using Fineman-Ross and ¹³C NMR methods. The values of r₁ (M₁ = ethylene) and r₂ (M₂ = α-olefin) showed an effect of the type of metallocene and of α-olefin on the structure of the copolymer obtained.     

Propene polymerization with a Mg(OC2H5)2-supported TiCl4 catalyst, 3. The role of benzoyl chloride

The catalyst systems Mg(OC₂H₅)₂/benzoyl chloride (BC)/TiCl₄ and Mg(OC₂H₅)₂/ethyl benzoate (EB)/TiCl₄ were prepared for the polymerization of propene. In case of the Mg(OC₂H₅)₂/BC/TiCl₄ catalyst, BC changes into the internal donor EB during the in situ preparation of the catalyst and the unchanged BC acts as additional donor after reaction with triethylaluminium (TEA). Catalyst activity and isospecificity were also studied for the two catalysts by changing the amounts of BC or EB in the polymerization of propene cocatalyzed with TEA.     

Effect of hydrogen on propene polymerization with solvay-type TiCl3/Cp2 TiMe2 catalyst

Polymerization of propene with a highly isospecific Solvay-type TiCl₃/Cp₂TiMe₂ catalyst in the presence and absence of hydrogen was investigated. It was found that hydrogen exerts almost no effect on the molecular weight and the stereoregularity of the resulting polypropylene. Furthermore, the H₂/D₂ exchange reaction hardly proceeds over the catalyst. To discuss this unusual behavior, plausible mechanistic explanations on the basis of the structure of active species are proposed.     

The effect of preparation conditions on the catalyst Nd(P507)3/H2O/Al(i-Bu)3 for the polymerization of styrene

The catalyst system neodymium phosphonate Nd(P₅₀₇)₃ /H₂O/Al(i-Bu)₃ for the polymerization of styrene was examined. Effects of the addition order of the catalyst components, catalyst aging time and aging temperature on the catalyst activity and the polymer characteristics were investigated. The catalyst activity for isospecific polymerization of styrene increases with aging time and reaches the maximum with a catalyst aged for 45 min at 70°C. The aging time that the catalyst needs to reach the highest activity for isospecific polymerization decreases with increasing aging temperature. The preformed catalyst and the in situ catalyst were compared with respect to the kinetic behavior of the styrene polymerization and the polymer characteristics.