Polymerization of vinyl chloride in the presence of modified Ziegler–Natta catalysts comprising long chain organoaluminum compounds

Polymerization of vinyl chloride in the presence of systems containing a transition metal compound/Lewis base and an organoaluminum compound of a different length of carbon chain have been carried out. The influence of the structure and the concentrations of particular components on the polymerization yield and molecular weight of the products has been determined. The polymerization of vinyl chloride proceeds according to the free radical mechanism, and the effectiveness of such types of initiators decreases with an increase in the length of the substituent chain in the organoaluminum chain. When using ethyl derivatives, the maximum degree of vinyl chloride conversion is about 75%, and for polystyryl or polyisoprenylaluminum of an average polymerization degree of 50–100, the conversion did not exceed 0.5%. The maximum polymerization degree of vinyl chloride in block copolymers containing polyisoprenyl or polystyryl units was 90–300.     

Polymerization of propylene by mixed Ziegler–Natta and metallocene catalysts

The polymerization of propylene using a mixture of racemic metallocenes and Ziegler–Natta catalysts was investigated. The polypropylene was obtained as a mixture of a fine powder and beads, with the powder being absorbed partially on the beads. The relative amount of the powder can be controlled by the concentration of the metallocene. The compatibility between the components of the mixed catalytic systems and the effect of the components on the rate of polymerization and on the properties of the new polymers were studied. The metallocene system dramatically affects the melt viscosity, isotacticity and molecular weight of the polymers. The two catalytic systems are able to act jointly, producing different polymers, for which separate melting and crystallization temperatures are obtained. © 1998 John Wiley & Sons, Ltd.     

Layer-lattices in Ziegler–Natta catalysts

Some layered inorganic compounds of interest in old and new polymerization processes by Ziegler-Natta stereospecific catalysis have been studied. The results are reported of an investigation concerning the crystallographic disorder phenomena in α-TiCl₃, VCl₃, FeCl₃, ball-milled α-MgCl₂, β-MgCl₂, and in a new catalytic system produced according to some recent trends in the field. Best fits are reported of the experimental x-ray diffraction patterns with patterns calculated for a theoretical model that accounts for structural disorder; the different fits indicate that disorder phenomena due to stacking faults are rather frequent in the examined compounds. The catalytic systems are more and more dispersed, and the maximum of dispersion in heterogeneous systems is reached for the recently proposed formulations.     

Ethylene polymerization reactions with Ziegler–Natta catalysts. I. Ethylene polymerization kinetics and kinetic mechanism

Kinetics of ethylene homopolymerization reactions and ethylene/1-hexene copolymerization reactions using a supported Ziegler–Natta catalyst was carried out over a broad range of reaction conditions. The kinetic data were analyzed using a concept of multicenter catalysis with different centers that respond differently to changes in reaction parameters. The catalyst contains five types of active centers that differ in the molecular weights of material they produce and in their copolymerization ability. In ethylene homopolymerization reactions, each active center has a high reaction order with respect to ethylene concentration, close to the second order. In ethylene/α-olefin copolymerization reactions, the centers that have poor copolymerization ability retain this high reaction order, whereas the centers that have good copolymerization ability change the reaction order to the first order. Hydrogen depresses activity of each type of center in the homopolymerization reactions in a reversible manner; however, the centers that copolymerize ethylene and α-olefins well are not depressed if an α-olefin is present in the reaction medium. Introduction of an α-olefin significantly increases activity of those centers, which are effective in copolymerizing it with ethylene but does not affect the centers that copolymerize ethylene and α-olefins poorly. To explain these kinetic features, a new reaction scheme is proposed. It is based on a hypothesis that the Ti—C₂H₅ bond in active centers has low reactivity due to the equilibrium formation of a Ti—C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4255–4272, 1999     

Polymerization of 4-phenyl-1-butyne catalyzed by metathesis and Ziegler–Natta catalysts

The polymerization of 4-phenyl-1-butyne was carried out using metathesis and Ziegler-Natta catalysts. Especially, the Fe(acac)₃-AlEt₃ catalyst with toluene as a solvent produced an extremely high molecular weight polymer of M_w ≈ 10⁶. Solubility of the polymers at room temperature in organic solvents such as benzene, toluene, dichloromethane, chloroform, and THF was excellent despite their high molecular weights. It has been indicated that the polymer prepared by the Fe(acac)₃-AlEt₃ catalyst is of cis form with a high stereoregularity. © 1993 John Wiley & Sons, Inc.     

Polymerization of ethylene at high temperature by vanadium-based heterogeneous Ziegler–Natta catalysts. I. Study of the deactivation process

Kinetics of the polymerization of ethylene initiated by heterogeneous vanadium-based Ziegler-Natta catalysts (VCI₃-1/3 AICI₃) have been studied at high temperature (160°C, 5 bars) and compared with a titanium-based system. For the V catalyst, the dependence of the polymerization activity versus time, with the nature and the concentration of the associated aluminum alkyl, has been investigated. Kinetic results have also been correlated with the oxidation state of vanadium in the polymerization conditions. Despite the relatively high initial activity a low productivity is obtained; it can be attributed to a very fast deactivation of the active sites due to the reduction of vanadium III into vanadium II. The effect of the nature of the alkyl aluminum component of the catalytic system on the reduction process is shown. A kinetic model for the polymerization is proposed. © 1993 John Wiley & Sons, Inc.     

Polymer-supported Ziegler–Natta catalysts. I. A preliminary study of catalyst synthesis

Polymer-supported Ziegler–Natta catalysts based on various polymer carriers were synthesized by different methods, including (1) loading TiCl₄ directly onto the polymer supports; (2) loading TiCl₄ onto the polymer supports modified by magnesium chloride (MgCl₂); (3) loading TiCl₄ onto the polymer supports modified by Grignard reagent (RMgCl); and (4) loading TiCl₄ onto the polymer supports modified by magnesium alkyls (MgR₂). The activity and kinetic features of the catalysts for ethylene polymerization were examined. Among the combinations tested, the best was found to be TiCl₄/n-Bu₂Mg.Et₃Al/poly(ethylene-co-acrylic acid) (92:8), which produced a catalyst of very high activity for ethylene polymerization. © 1994 John Wiley & Sons, Inc.     

Polymerization of ethylene using a high-activity Ziegler–Natta catalyst. I. Kinetic studies

Factors affecting the particular shape of kinetic rate–time profiles in the polymerization of ethylene with a MgCl₂-supported TiCl₄ catalyst activated by Al(C₂H₅)₃ have been investigated. Examination of the dependence of the polymerization rate on the concentration of Al(C₂H₅)₃ resulted in a Langmuir–Hinshelwood rate law. Analysis of the polymerization rate as a function of the polymerization temperature gave about 46 kJ mol^?1 for the overall activation energy. Examination of the rapid decay of the polymerization rate with time showed that this decay is represented better by a first-order decay law than by a second-order one. © 1993 John Wiley & Sons, Inc.     

Polymerization of mono-substituted acetylenes with a liquid crystalline moiety by Ziegler–Natta and metathesis catalysts

Polymerization of five monomers, 1-[p-(trans-4′-alkylcyclohexyl)phenoxy]alkyne (i.e., PCH001A, where PCH, 0, 01 and A represent phenylcyclohexyl mesogenic moiety, number of carbon in an alkyl group attached to cyclohexyl group, ether linkage + number of methylenic units in the spacer between phenoxy and acetylenic groups, and terminal acetylene, respectively) were carried out using Ziegler-Natta and metathesis catalysts. All polymers were soluble in organic solvents such as benzene, chloroform, and THF. A liquid crystalline phase was observed in the polymers of PCH303A and PCH503A through the polarized optical microscope and DSC measurements. Polymerization of PCH003A by the Fe(acac)₃-AlEt₃ catalyst yielded a high-molecular-weight polymer with M_w = ca. 3 × 10⁶. © 1993 John Wiley & Sons, Inc.     

New Ziegler–Natta polymerization catalysts and new polymers

Models for the explanation of the stereospecific behaviour of Ziegler-Natta catalysts, homogeneous and heterogeneous, are discussed. Structural data on new types of stereoregular polymers, obtained with homogeneous catalysts, are reported.     

Control of composition in ethylene copolymerizations using magnesium chloride supported Ziegler–Natta catalysts

Incorporation of a sterically hindered phenol (2,6-di-tert-butyl-4-methylphenol) during the preparation of MgCl₂-supported titanium catalysts coupled with the use of an aluminum alkyl activator modified with the same phenol and an electron donor such as ethyl benzoate allows the systematic modification of the reactivity ratios of ethylene and 1-olefin copolymerizations. The polymers obtained tend to be largely random with a tendency toward alternating at high comonomer incorporation. Very low density LLDPE copolymers have been prepared in stable slurry polymerizations. The same catalysts allow the preparation of copolymers with dienes.     

Synthesis of polypropylene-co-p-methylstyrene copolymers by metallocene and Ziegler–Natta catalysts

This paper discusses the copolymerization reaction of propylene and p-methylstyrene (p-MS) via four of the best-known isospecific catalysts, including two homogeneous metallocene catalysts, namely, {SiMe₂[2-Me-4-Ph(Ind)]₂}ZrCl₂ and Et(Ind)₂ZrCl₂, and two heterogeneous Ziegler–Natta catalysts, namely, MgCl₂/TiCl₄/electron donor (ED)/AlEt₃ and TiCl₃. AA/Et₂AlCl. By comparing the experimental results, metallocene catalysts show no advantage over Ziegler–Natta catalysts. The combination of steric jamming during the consective insertion of 2,1-inserted p-MS and 1,2-inserted propylene (k₂₁ reaction) and the lack of p-MS homopolymerization (k₂₂ reaction) in the metallocene coordination mechanism drastically reduces catalyst activity and polymer molecular weight. On the other hand, the Ziegler–Natta heterogeneous catalyst proceeding with 1,2-specific insertion manner for both monomers shows no retardation because of the p-MS comonomer. Specifically, the supported MgCl₂/TiCl₄/ED/AlEt₃ catalyst, which contains an internal ED, produces copolymers with high molecular weight, high melting point, and no p-MS homopolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2795–2802, 1999     

Ziegler–Natta catalysts on silica for ethylene polymerization

The amount of dibutylmagnesium (DBM) or triethylaluminum (TEAL) that reacted with silica at 55–60°C depended on the silica calcining temperature. Lower silica calcining temperatures resulted in more Mg or Al fixed to the silica surface, indicating greater amounts of DBM or TEAL reacting with the silica. The amount of the metal alkyls butyl(octyl) magnesium ethoxide, ethylaluminum dichloride, tri-n-hexylaluminum, and diethyl(ethyldimethylsilanolato) aluminum that reacted with 600°C calcined silica was also determined. The metal alkyl can react with the silica at two sites, a surface hydroxyl group and a siloxane group. The silica surface hydroxyl groups can be chemically converted to trimethylsilyl groups so that only the siloxane groups are available for attack. After the metal alkyl was reacted with silica, the resulting intermediate was treated with titanium tetrachloride to yield an ethylene polymerization catalyst in the presence of TEAL. When no metal alkyl was employed, titanium tetrachloride reacted only with the silica surface hydroxyl groups to yield a weakly active ethylene polymerization catalyst.     

A kinetic method of reactivity ratio measurement in olefin copolymerization with Ziegler–Natta catalysts

An efficient kinetic method of reactivity ratio measurement for binary copolymerization of gaseous monomers⁴ that does not require the measurement of copolymer composition and can be applied to the data obtained in a single copolymerization run was modified and applied to olefin copolymerization with heterogeneous Ziegler–Natta catalysts. Estimated r₁ and r₂ values for pairs like ethylene-propylene and propylene-1-butene agree favorably with published data.     

Ethylene–propylene copolymerization initiated with solubilized Ziegler–Natta macromolecular complexes. I. Determination of kinetic parameters

Copolymerization of ethylene with propylene (E–P) was initiated with soluble polystyrene –butadiene–Li/TiCl₄ complexes in toluene leading to vinylic-olefinic based block copolymers. The activity of the system was measured at a constant ratio r = Li/Ti for different feed compositions. From measurements of the amount of copolymers produced, a direct determination of the efficiency of the catalytic system was made. This efficiency was found to be close to that obtained for homopolymerizations of C₂H₄ and C₃H₆ initiated with the same catalytic complex (? 80% with respect to the concentration of “carbon-titanium” bonds). Both the measured values of the efficiency and the determination of the molar masses of the polyolefinic block are consistent with a living character of the system involved in the E–P copolymerization. In such conditions well-defined linear [styrene]-b-[ethylene-co-propylene] copolymers were obtained. Furthermore, ¹³C NMR analyses allowed determination of the comonomer reactivity ratios, the values of which indicate an E–P random copolymerization. From both these values and those of the absolute rate constants of propagation determined for the homopolymerization of C₂H₄ and C₃H₆ initiated with the same catalytic system, the absolute rate constants of cross-propagation were deduced.     

Organic nanoparticles as fragmentable support for Ziegler–Natta catalysts

A fragmentable support material for Ziegler–Natta catalysts is presented based on micrometer‐sized aggregates of polystyrene nanoparticles. Hydroxyl anchoring groups are introduced by copolymerization of hydroxymethylstyrene in emulsion process to immobilize the catalysts. The catalytic activity in ethylene slurry polymerizations is found to be directly correlated to the hydroxyl group content of the supports. Furthermore, the fragmentation behavior of dye‐labeled support aggregates into the initial nanoparticles is demonstrated using laser scanning confocal fluorescence microscopy as a nondestructive method. These supported catalysts fulfill two important design criteria, high fragmentability and high catalyst loading, and produce high‐density polyethylene with medium molecular weight distributions (MWDs = 3–4). These values lie between those obtained using single‐site metallocene‐based (narrow MWD < 3) or inorganic supported multi‐site Ziegler–Natta‐based (broad MWD = 4–12) polymerizations without the need of blending. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 15–22     

Reduced titanium dioxide as support for Ziegler–Natta catalysts

Titanium tetrachloride heterogenized on reduced TiO₂ has been studied as a catalyst for ethylene polymerization. The catalyst has good storage stability and exhibits good activity for ethylene polymerization. The polymer chains grow linearly during ca. 1 h, giving an average molecular weight of up to 2.5 × 10⁶ which indicates that practically no β-elimination occurs. The activity of the catalyst at 50°C, based on Ti(III), is 7.6 × 10⁶ PE/mol Ti h bar and based on the quantity of polyethylene formed it is 1.25 × 10⁶ g PE/mol Ti h bar. The molecular weight of the polymer can be controlled with the addition of hydrogen, under 0.5 bar hydrogen, polyethylene with a molecular weight of 411,000 and a relatively low polydispersity index of 2.2 is obtained. The catalyst shows good thermal stability; the Arrhenius activation energy is 31.8 kJ/mol for the polymerization. The catalyst is also active for propylene polymerization, giving 3 × 10⁶ g PP/mol Ti h bar with the high isotacticity of 93%. © 1994 John Wiley & Sons, Inc.     

Crown ethers as ligands for stereospecific polymerization by Ziegler–Natta catalysts

Some new TiCl₄/Crown ether complexes were synthesized and used as polymerization catalysts with AlEt₃ or AlEt₂Cl as cocatalyst for the stereospecific polymerization of 1,3-butadiene. As with most of the nucleophilic ligands the addition of crown ethers to Ziegler–Natta catalytic systems results in a decrease of the polymer conversion. But the Al/Ti molar ratio appears to be less critical for the complexed systems than for the uncomplexed ones. The presence of the crown ether in the surroundings of the catalytic sites presumably protects them from an excess of the organoaluminum cocatalyst. The side groups of the crown ether do not influence the microstructure of the polybutadiene obtained but they change the activity of the catalytic systems. Thus, the electron-donating effect of the macrocyclic ligands seems to be less important than the sterical effect due to the rigidity and to the hole size of the crown ether.     

Ethylene–styrene thermoplastic copolymers prepared with supported Ziegler–Natta catalysts

The magnesium chloride supported Ziegler–Natta catalysts are able to copolymerize ethylene and styrene in conditions of high activity. Different parameters, including catalyst type, monomer ratio, temperature and Lewis bases, allow variation of the activity and reactivity ratio. The incorporation of styrene in the copolymer remains always rather limited in moles. The products obtained contain less than 20% styrene in weight, and seem very similar in structure to linear low-density polyethylenes (LLDPE) obtained with the same catalyst: the melting temperature is only about 5°C lower than that of pure polyethylene. The polymer can be fractionated by solvents in a similar manner to LLDPE, and contains a styrene-enriched fraction, but homopolystyrene production has never been observed.     

High activity magnesium chloride supported catalysts for olefin polymerization. XXIX. Molecular basis of hydrogen activation of magnesium chloride supported Ziegler–Natta catalysts

Hydrogen (pH₂ = 72 torr) increases the rate of propylene polymerization by a MgCl₂/ethyl benzoate/p-cresol/AlEt₃/TiCl₄-AlEt₃/methyl-p-toluate catalyst (CW-catalyst) by two-to three-fold which corresponds closely with the increase in the number of active sites as counted by radiolabeling with tritiated methanol. The oxidation states of titanium in decene polymerizations by the CW-catalyst were determined as a function of time of polymerization (t_p). In the absence of H₂, all [Ti⁺ⁿ] for n = 2, 3, 4 remain constant during a batch polymerization. In the presence of H₂ and within 5 min of t_p, [Ti⁺²] decreases by an amount, corresponding to 15% of the total titanium and [Ti⁺³] increases by the same amount, while [Ti⁺⁴] is not changed. Therefore, three-fourths of the H₂ activation result from oxidative addition processes. The remaining one-fourth of the H₂ activation may be attributed to the activation of previously deactivated Ti⁺³ ions by hydrogenolysis. Monomer converts some of the EPR silent Ti⁺³ sites to EPR observable species resulting in their activation.