Propylene Homopolymerization Research Articles

Synthesis and characterization of branched polypropenes obtained by metallocene catalysis

The homopolymerization of propene, 4-methyl-1-pentene, 1-octene and the copolymerization of propene with 4-methyl-1-pentene and 1-octene, respectively, was carried out with the isospecific metallocene catalyst system rac-[(dimethylsilylene)bis(2-methylbenzo(e)indenyl)]zirconium dichloride/methylaluminoxane at 30°C in toluene. By variation of the monomer ratio, it is possible to produce copolymers in the entire composition range. The activity, the amount of comonomer insertion, and the molecular masses obtained in the propene/1-octene copolymerization are significantly higher compared to the respective values of the system propene/4-methyl-1-pentene. It is possible to synthesize polymers with glass transition temperatures ranging from −65 up to 26°C. Whereas the incorporation of more than 20 mol-% 1-octene leads to amorphous polymers, the propene/4-methyl-1-pentene copolymers with less than 15 and more than 60 mol-% 4-methyl-1-pentene are semicrystalline. All melting points vary in the range from 50 to 225°C. Wide angle X-ray scattering measurements indicate an increase of the γ-modification compared to the γ-modification with increasing comonomer content and crystallization temperature. Typical supermolecular morphologies different from spherulites and known for the γ-phase of the isotactic polypropene homopolymer are observed for the copolymers by polarized light microscopy.

Metallocene dichlorides bearing acenaphthyl substituted cyclopentadienyl rings: preparation and polymerization behavior

The unbridged complex [bis( η 5-7,9-diphenylcyclopenta[ a]acenaphthadienyl)] zirconium dichloride ( 8) and two asymmetric ethylene bridged metallocenes {bis[1,2-( η 5-7,9-diphenylcyclopenta[ a]acenaphthadienyl)-1-phenyl] ethane} zirconium dichloride ( 9) and {[1-( η 5-7,9-diphenylcyclopenta[ a]acenaphthadienyl)-2-phenyl-2-( η 5-9-fluorenyl)] ethane} zirconium dichloride ( 10) were prepared and used as catalysts for ethene and propene homopolymerization after activation with MAO. Whereas zirconocenes 8 and 9, that bear two acenaphthyl substituted Cp-rings, have only moderate activity, 10 produces polyethene with high activity and high molecular weight. In propene polymerization only atactic polymer was formed and the chain termination occurred mainly via β-methyl elimination. The solid state structures of compounds 8, 9 and 10 were determined by means of X-ray diffraction analysis.

Homogeneous Binary Zirconocenium Catalyst Systems for Propylene Polymerization. 1. Isotactic/Atactic Interfacial Compatibilized Polymers Having Thermoplastic Elastomeric Properties

Polypropylene with thermoplastic elastomeric properties was synthesized by homopolymerization of propylene using two metallocene catalysts of different stereospecificities: rac-ethylenebis(1-η5-indenyl)zirconium dichloride or rac-dimethylsilylenebis(1-η5-indenyl)zirconium dichloride as isospecific catalyst precursors and ethylenebis(9-η5-fluorenyl)zirconium dichloride as an aspecific precursor. The catalysts formed by activation of the precursors with triphenylcarbenium tetrakis(pentafluorophenyl)borate and triisobutylaluminum exhibit a very high activity of 5 × 107 g of PP/([Zr][C3H6] h). Products ranging from tough plastomers to weak elastomers were obtained by varying the ratio of the two types of precursors. The polymers containing less than half of the isotactic fraction display excellent thermoplastic elastomeric properties, which is attributable to an interconnected crystalline superstructure in an amorphous continuum compatibilized and bound together by a stereoblock copolymer at the interface against macrophase separation. Materials exhibiting elastic recoveries of 97−98%, which are relatively independent of elongation up to 500%, were obtained.

Syndiotactic‐specific polymerization of propene with a Ni‐based catalyst

AbstractPolymerization of propene at −78°C in the presence of a homogeneous catalytic system based on a Ni(II) diimine derivative and methylaluminoxane affords prevailingly syndiotactic crystalline poly(propylene) (rr triad content ≈80%). 13C NMR analysis of the polymer microstructure indicates that the stereochemistry of the monomer insertion is controlled by the configuration of the methine carbon of the growing chain end (unlike‐1,3 asymmetric induction). This is the first example of stereospecific homopolymerization of propene promoted by a late transition metal catalyst.

Preparation of soluble TiCl 4 catalyst modified with some metal chlorides and its use for ethylene and propylene homopolymerization

Polymerizations of ethylene or propylene were conducted in toluene employing the soluble catalytic system TiCl 4. THF/AlCl 2(C 2H 5)/Al(i-C 4H 9) 3 combined with different metal chlorides (CoCl 2,MgCl 2 or ZnCl 2) complexed with tetrahydrofuran (THF). The catalyst activity was strongly dependent upon the metal chloride used as modifier. A clear increase of catalyst activity in ethylene polymerization was observed when the Co/Ti or Mg/Ti mole ratio was increased up to 2 and then decreased markedly. In a similar way, the catalyst activity in propylene polymerization was strongly dependent upon the amount and kind of metal chloride used as modifier.

Polymerization of ethylene and propylene with homogeneous titanocene catalysts modified by trimethylsilanol

Polymerizations of ethylene and propylene were conducted with catalysts based on titanium compounds (TiCl 4 or CpTiCl 3) modified by trimethylsilanol (TMS). The convenient conditions of catalyst preparation and polymerization were investigated such as ageing time, Si/Ti mole ratio, catalyst concentration, type of alkylaluminum compound used as cocatalyst and Al/Ti mole ratio. The influence of these parameters on the homopolymerization of ethylene and propylene is then described in detail. The polymerization activities were found to be strongly dependent upon catalyst preparation and polymerization conditions. Electron paramagnetic resonance (EPR) analyses were conducted with different Al/Ti mole ratios for elucidating the influence of the Ti oxidation state on the catalyst properties. This work reports a plausible mechanism for the polymerization on the basis of these results.

Elementarprozesse der Ziegler‐Katalyse, 6 Ethylen‐ und propenhomopolymerisation mit den stereorigiden katalysatorsystemen iPr[FluCp]ZrCl2/MAO und Me2Si[Ind]2ZrCl2/MAO

AbstractThe ethylene and propene homopolymerization was investigated by means of the Cs‐symmetric [2,4‐cyclopentadien‐1‐ylidene(isopropylidene)fluoren‐9‐ylidene]zirconium dichloride/methylaluminoxane (iPr[FluCp]ZrCl2/MAO) and the C2‐symmetric [(dimethylsilylene)bis(η5‐inden‐1‐ylidene)]zirconium dichloride/methylaluminoxane (Me2Si[Ind]2ZrCl2/MAO) catalyst systems in toluene. Surprisingly, the Cs‐symmetric catalyst polymerizes propene faster than ethylene. The main results of the kinetic analysis are a first‐order dependence on the concentration of Zr but a bell‐shape in the plot of the polymerization rate versus log([Al]: [Zr]). This is true for both catalyst systems. Furthermore with increasing [Al]:[Zr] ratio the fraction of rmrr pentads is decreased continuously with the Cs‐symmetric catalyst; in the same direction the molecular weights are decreased. On the contrary with the C2‐symmetric catalyst the stereospecificity and the molecular weights remain constant. The kinetic results reflect the complex role of the MAO, i.e. the existence of sterically more and more tight contact species between metallocene and MAO components with increasing [Al]: [Zr] ratio. The different behaviour of the two catalyst systems concerning stereospecificity and molecular weights of the polymers are due to different symmetry and different size of the angle between the planes of the π‐ligand systems.

Influence of the monomer nature on the activity of the supported titanium catalyst of polymerization of α-olefins

The paper is based on a kinetic analysis of the copolymerization and sequential homopolymerization of ethylene and propylene with a supported titanium-magnesium catalyst in the gas phase and in the presence of a solvent. The specific rate of polymerization and the reactivity constants of the monomers were calculated, using found values of the solubility constants for ethylene and propylene in the polymer matrix. It was found that with propylene enrichment of the monomer mixture the copolymerization rate is increased, and the activation of ethylene polymerization after the polymerization of propylene is unrelated to modification of active centres. It is proposed that an increase in the amorphous phase content in the nascent polymer product makes for facilitated access of monomer throughout the polymer film to active centres on the catalyst surface, and leads to an increase in the specific activity of the catalyst system.

Propene polymerization with MgCl2 supported Ziegler catalysts: Activation by hydrogen and ethylene

AbstractComplementary experiments confirm the recent findings that the rate of propene polymerization is temporary enhanced if a small amount of ethylene is introduced during the polymerization, normalizing after consumption of ethylene by copolymerization. In addition, the study of the sequence distribution of propene monomeric units in the copolymerization carried out under various conditions revealed that the activation by ethylene does not involve the propagation steps, but the re‐initiation after deactivation. A similar temporary activation effect was observed after the addition of small amounts of hydrogen. In this case, however, hydrogen is not consumed. Thus, the deactivation observed after the initial rate enhancement is due to another reason. The deactivation could be shown to be reversible after removal of the adsorbed hydrogen when either ethylene or hydrogen was added again to allow re‐initiation of the polymerization. One of the important reasons of the continuous decrease of the propene homopolymerization rate may be due to the fact, that, after a transfer step, the re‐initiation of polymerization does not take place spontaneously. Small amounts of ethylene or hydrogen allow the reinitiation to take place, at least for some kind of active sites.

Copolymerization of propylene with a small amount of ethylene using a MgCl2/TiCl4 and a TiCl3 catalyst system

Copolymerization of propylene with a small amount of ethylene and homopolymerization of propylene were performed using a highly active MgCl2/TiCl4-Et3Al/ethyl benzoate(EB) and a conventional TiCl3-Et2AlCl catalyst systems. The obtained polymers were fractionated into n-decane (C10) soluble and insoluble portions. In all homopolymer fractions with the investigated catalyst systems and copolymer fractions with TiCl3 catalyst system, the inversion of the direction of arrangement of the propylene unit was not observed by 13C-NMR analysis. On the other hand, in C10 soluble fractions of copolymer using MgCl2/TiCl4 catalyst system, regardless of the presence of EB, a significant amount of the inversion unit was detected.

The catalytic activity of Ti IV and Ti III compounds in copolymerization of butadiene and propylene

The catalytic activity of tetramethylsilylmethyl derivatives of Ti III and T IV compounds in copolymerization of butadiene and propylene has been studied. It is shown that individual Ti IV compounds do not initiate homo- or copolymerization of these monomers in the temperature range of −30°C to +20°C. Alkyl derivatives of Ti III polymerize butadiene, forming polybutadiene-1,2 and are inactive with respect to propylene. In combination with Lewis acids silylmethyl derivatives of Ti III initiate polymerization of propylene and butadiene. The reaction of (CH 3) 3SiCH 2TiCl 3 with C 2H 5Li, and of TiCl 4 with (CH 3) 3SiCH 2Li at low temperatures was studied. It is shown that haloalkyl Ti III derivatives are formed under these conditions, and that the latter initiate copolymerization, including alternating copolymerization, and homopolymerization of butadiene and propylene.

Mechanism of Ziegler‐Natta polymerization of propylene and α‐d‐propylene

AbstractRates of propylene homopolymerization and α‐d‐propylene‐propylene copolymerization were determined by using constant‐pressure polymerization conditions. It could be demonstrated that the rate of propylene homopolymerization was constant under the conditions used. However, the initial rate of copolymerization was faster and decreased with time to the rate obtained for propylene homopolymerizations. The higher initial copolymerization rate was attributed to the stabilization of potentially active centers in solution when the deuterated monomer was present. These active centers are assumed to be formed by reactions of tetravalent titanium with monomer. These active centers, which are formed in solution, are said to be destroyed by isotopically controlled reactions, i. e., abstraction of the hydrogen or the α‐deuterium atom from these monomer‐alkylated species in solution or at the interface. These active centers are believed to be adsorbed and/or chemisorbed onto the precipitated catalyst surface and to be responsible for a polymer of considerably lower steric order. This scheme predicts a stereoregular polymer of high molecular weight produced by polymerization on a Ti(III) surface and a largely amorphous polymer of lower molecular weight produced by adsorbed and/or chemisorbed species. This prediction was verified by fractionation of the deuterated polymers into crystalline and amorphous portions.

Kinetics of the ethylene‐propylene copolymerization

AbstractThe results obtained from a systematic kinetic study of ethylene‐propylene copolymerization in the presence of catalysts prepared from Al(C6H13)3 and VCl4, already reported are briefly summarized.The considerable increase of the overall copolymerization rate, observed with the increase of the ratio of ethylene to propylene in the reacting liquid phase, cannot be explained only on the basis of the values of the kinetic constants of propagation, but it is also necessary to admit a variation in the concentration of the number of growing chains. Some experimental evidences are indicated proving this hypothesis.This result cannot be extended to the ethylene‐propylene copolymerization in the presence of other catalytic systems acting through an anionic co‐ordinated mechanism, for which the ratio between the rates of ethylene and propylene homopolymerization is very close to the value of the reactivity ratio of ethylene.Finally, an equation is proposed which interprets, to a good approximation, the values of the overall rate of the copolymerization process in the presence of the catalytic system Al(C6H13)3—VCl4.