Jürgen Suhm

Influence of metallocene structures on ethene copolymerization with 1-butene and 1-octene

Abstract Ethene/1-octene and ethene/1-butene copolymerization using various methylaluminoxane-activated metallocene catalysts, e.g. silylene-bridged substituted bisindenyl zirconocene systems and halfsandwich titanocene, was performed at 40°C in toluene. The influence of the ligand substitution on comonomer incorporation, catalyst activity, molar mass, molar mass distribution, degree of polymerization and copolymerization parameters was investigated in ethene/1-octene copolymerization at constant comonomer ratio and in ethene/1-butene copolymerization as a function of varying ethene/1-butene feed mass ratios. In ethene/1-octene copolymerization the highest comonomer incorporation was achieved with MAO-activated Me 2 Si(Me 4 Cp)( N - tert -butyl)TiCl 2 catalyst. Best performance in terms of comonomer incorporation combined with high catalyst activity and molar mass was found for silylene-bridged bisindenylzirconocenes, where 2-methyl substitution promoted high degree of polymerization and benzannelation accounted for improved catalyst activity, comonomer incorporation and randomness of comonomer incorporation. In ethene/1-butene copolymerization at high 1-butene feed content silylene-bridged substituted bisindenyl systems showed polymerization characteristics similar to that of ethene/1-octene copolymerization. The influence of 2-methyl substitution on activity and comonomer incorporation was significant only at low 1-butene feed content. Storage moduli and glass transition temperature of the poly(ethene-co-1-butene) copolymers decreased with increasing 1-butene content.

Temperature dependence of copolymerization parameters in ethene/1‐octene copolymerization using homogeneous rac‐Me2Si(2‐MeBenz[e]Ind)2ZrCl2/MAO catalyst

Ethene was copolymerized with 1-octene using homogeneous MAO-activated rac-Me2Si(2-MeBenz[e]Ind) 2 ZrCl 2 at constant ethene concentration with temperature varying between 0 and 60°C to determine a temperature dependence of copolymerization parameters. At constant 1-octene and ethene concentration (constant ethene/1-octene feed molar ratio) 1-octene incorporation decreased with increasing temperature. Furthermore, when ethene/1-octene molar ratio was varied by varying the temperature keeping 1-octene concentration and ethene pressure constant, increasing temperature accounted for lower molecular masses without affecting 1-octene incorporation. An explanation for the observed temperature dependence of the copolymerization parameters is presented, considering the solution-enthalpy of the gaseous ethene in the solvent. In all cases amorphous poly(ethene-co-1-octene) with 1-octene content varying between 20 and 40 mol % was obtained.

Short and long chain branching of polyethene prepared by means of ethene copolymerization with 1-eicosene using MAO activated Me2Si(Me4Cp)(NtBu)TiCl2

Ethene copolymers with 1-eicosene were prepared using the methylaluminoxane (MAO) activated dimethylsilanediyl (tetracyclopentadienyl) (ter-butylamido)- titanium dichloride (Me 2 Si(Me 4 Cp)(N t Bu)TiC1 2 , CBT) catalyst system in slurry polymerizations. The thermal behavior of the polymers was studied by differential scanning calorimetric (DSC) measurements in order to investigate the influence of long alkyl-branches on polyethene crystallinity, Upon increasing the incorporation of 1-eicosene from 0 to 50 wt.-%, the melting temperature decreased from 135°C to 35°C. The presence of a second peak in the DSC curves of ethene/1-eicosene copolymers with an incorporation of 1-eincosene exceeding 39 wt.-% was attributed to side chain crystallization. CBT is well known for introducing long chain branches (LCB) into polythene. Accordingly, the presence of additional long hain branches (with a chain length of more than 100 carbon atoms) was detected using rheological measurements. In oscillatory and creep tests, samples with low incorporation of 1-eicosene showed a behavior typical of long chain branched polymers. Poly (ethene-co-1-eicosene)s with high incorporation of 1-eicosene behaved like linear polymers, whereas ethene homopolymers contained less LCB. A long chain branching index (BI) was defined using terminal relaxation times. A correlation between BI and 1-eicosene content in the feed, as well as the number of long chain branches was established.

Influence of comonomer incorporation on morphology and thermal and mechanical properties of blends based upon isotactic metallocene-polypropene and random ethene/1-butene copolymers

Blends of isotactic polypropene (i-PP) with random ethene/1-butene (EB) copolymers containing 10, 24, 48, 58, 62, 82, and 90 wt % 1-butene were prepared in order to examine the influence of the EB molecular architecture on the morphology development as well as on the thermal and mechanical properties. Compatibility between i-PP and EB increased with increasing 1-butene content in EB to afford single-phase blends at a 1-butene content exceeding 82 wt %. The morphology was investigated using AFM and TEM. Improved compatibility accounted for enhanced EB dispersion and interfacial adhesion. Highly flexible as well as stiff blends with improved toughness were obtained.

Propene polymerization with rac-Me2Si(2-Me-Benz[e]Ind)2ZrX2 [X = Cl, Me] using different cation-generating reagents

Propene was polymerized with methylaluminoxane (MAO) and cationic activated ruc-dimethylsilylene-2-methyIbenz[e]indenylzirconocene [MBI-CI2] and [MBI-Me2]. For cationic activation of the MBI-Me2 system tris(pentafluoropheny1)borane [I], N,N-dimethylanilinium tetra(pentafluoropheny1)borate [11] or trityl tetra(pentafluoropheny1)borate [111] were used. The MAO-activated dimethyl complex showed higher activity with respect to the dichloride system using high catalyst concentrations and [Al]/[Zr] ratios. Most effective cationic activator for MBI-Me2 was N,N-dimethylanilinium tetra(pentafluoropheny1)borate [11] in combination with Al(i-Bu3). Using tris(pentafluoropheny1)borane [I] at different polymerization conditions or N,N-dimethylanilinium tetra(pentafluoropheny1)borate [11] in combination with Al(Et)3 no propene polymerization was observed due to the occurrence of reduction of the catalytically active site.

New molecular and supermolecular polymer architecturesvia transition metal catalyzed alkene polymerization

Superstructure formation during crystallization has been examined as a function of isotactic poly(propene) and poly(ethene) molecular architectures, tailored by means of metallocene catalyzed propene polymerization, metallocene catalyzed ethene/alk-1-ene copolymerization, and nickel-catalyzed migratory insertion polymerization of ethene to afford methyl-branched poly(ethene) without using comonomers. The role of steric irregularities in the chain resulting from false insertion in stereoselective polymerization or from short chain branching, respectively, was investigated. Randomly distributed regio- and stereo-regularities in isotactic poly(propene) chains and variation of crystallization temperature were the key to controlled poly(propene) crystallization and predominant formation of the γ-modification. Poly(propene) melting temperature increased with increasing isotactic segment length between stereo- and regio-irregularities. Superstructures of isotactic γ-poly(propene) were analyzed by means of light and atomic force microscopy. Both types of short-chain branched poly(ethene)s, prepared by ethene/oct-1-ene copolymerization and migratory insertion homopolymerization, showed similar dependence of melting temperature on the degree of branching, calculated as the number of branching carbon atoms per 1000 carbon atoms. Phase transitions were monitored by means of wide angle X-ray scattering and pressure–volume–temperature measurements. Atomic force microscopy was applied to image both lamella- and fringed micelle-type superstructures as a function of the degree of branching.

Microstructure and pressure—volume—temperature properties of ethene/1-octene random copolymers

Copolymers of ethene and 1-octene were synthesized covering the entire composition range by means of the methylalumoxane activated rac-Me 2 Si(2-MeBenz[e]Ind) 2 ZrCl 2 catalyst. 13 C-NMR spcctroscopy revealed first-order Markov statistics to be reasonably suited for the description of the copolymer sequence distribution. Characteristic parameters of ethene/1-octene copolymers were obtained by evaluation of pressure-volume-temperature data using the Flory-Orwoll-Vrij equation-of-state theory. The characteristic pressure could not be correlated with 1-octene comonomer incorporation when assuming validity of the mixing rules known for homopolymer blends, whereas the characteristic specific volume and characteristic temperature are independent of copolymer composition within experimental errors. A possible explanation is presented for why the attempts to predict the characteristic pressure of ethene/1-octene copolymers from the corresponding homopolymer parameters fail using Florys mixing rules.

Branched Polyethenes Prepared via Olefin Copolymerization and Migratory Insertion

Branched polyethenes with variable alkyl side chains were prepared via three routes: (1) metallocene-catalyzed copolymerization of ethene with propene, 1-octene, 1-eicosene, (2) simultaneous ethene polymerization and copolymerization of in-situ formed 1-alkenes resulting from ethene oligomerization, using a blend of Ni- and Ti-based catalysts (“hybrid catalysts”), and (3) Ni- and Pd-catalyzed ethene homopolymerization with branching occurring due to migratory insertion. The resulting families of materials included high density, low and ultralow density semierystalline polyethenes as well as highly flexible and elastomeric polyethenes. The degree of branching (DB), as measured by the number of branched C/1000 C, was correlated with comonomer incorporation, catalyst structure, polymerization conditions, polyethene melting temperature and melting enthalpy. Polyethenes prepared by ethene/1-olefin copolymerization were compared with branched ethene homopolymers. Linear low density polyethenes with DB<50, produced with Ni-catalysts, resembled poly(ethene-co-propene). Highly branched polyethene elastomers were applied as toughening agents and blend components of isotactic polypropene in order to improve polypropene’s impact resistance.