The new C 1-symmetric complexes rac-[1-(9-η5-fluorenyl)-2-(2-methylbenz[e]-1-η5-indenyl)ethane]zirconium dichloride (14a), rac-[1-(9-η5-fluorenyl)-2-(4,5-cyclohexa-2-methyl-1-η5-indenyl)ethane]zirconium dichloride (14b), and rac-[1-(9-η5-fluorenyl)-2-(5,6-cyclopenta-2-methyl-1-η5-indenyl)ethane]zirconium dichloride (15) were prepared in up to 93% yield. These compounds, activated with methyl aluminoxane, exhibit high active propene polymerization rates which remain constant over hours, even at elevated polymerization temperatures of 50 and 70 °C. The two different coordination sites of these “dual-side” catalysts lead to isotactic polypropenes with variable amounts of stereoerrors, depending on the monomer concentration. The 2-methyl substituent of the indenyl ligands results, at the same time, in significantly increased molecular weights of the polymer products (up to 2.3 × 105 g mol-1), the bulk properties of which can be adjusted from flexible, semicrystalline thermoplastic to excellent thermoplastic elastic.

No abstract

SUMMARY: The polymerization behavior of three linear asymmetrically substituted dienes, i.e. 6-phenyl-1 ,5-hexadiene (A), 7-methyl-1,6-octadiene (B) and R(+)-5,7-dimethyl-1,6-0ctadiene (isocitronellene, C) is reported in order to study the effect of substitution at one vinylic group. Homopolymerization of these monomers with the catalyst system rac-Et[Ind]2ZrC12/MA0 resulted in no reaction products in the case of monomer A and in polymers with % , = 3.5 kg/mol and % = 14.0 kg/mol with the monomers B and C, respectively. According to NMR analysis, the vinylene end group of isocitronellene remained untouched during polymerization, which excludes the possibility of cyclopolymerization or crosslinking. Copolymerization of isocitronellene with propene resulted in incorporation of the diene (15.6 mol-%) equal to the stoichiometric ratio in the monomer feed, with a relatively high catalyst activity. The degree of incorporated isocitronellene is inversely related to the polymerization temperature, providing control over crystallinity (isotacticity) and molecular weight of the copolymer. The isocitronellene homo-and copolymers could be epoxidized quantitatively and brominated to an extent of 90%. Perfluorohexyl iodide was grafted onto the isocitronellene/propene copolymer by radical reaction (conversion 80%), yielding a poly(a-olefin) with fluorinated side chains.

Propene and 7-methyl-1,6-octadiene (MOD) were copolymerized with the catalyst system rac-Et[Ind]2ZrCl2/MAO in semibatch reactions and under constant comonomer concentrations using an autoclave setup that is equipped with an ATR-FTIR sensor coupled with a dosage system for the liquid MOD comonomer. The concentration of the monomer propene is regulated precisely in both types of polymerization by a gas flow controller. This setup enables to monitor the MOD concentration on-line and in real-time during the reaction by following characteristic bands arising from the double bonds. Copolymers with poorly defined incorporation data and thermal properties were obtained without control of the MOD concentration in time. This is caused by a nonuniform distribution of the MOD units over the polymer chains due to a relatively large shift of the MOD concentration during the copolymerization reaction. By means of solvent extraction fractionation experiments, these copolymers could be fractionated into three fractions with different amounts of incorporated MOD, varying from 11.5 to 7.2 mol %. Functional copolymers with uniform architectures (up to 30.5 mol % incorporated MOD) were prepared by using the on-line ATR-FTIR data to control the MOD concentration during the copolymerization reactions.

It is well known that the mechanical properties of highly isotactic polypropene depend on the crystalline structure of the material. Up to now, the polymer properties were modified by varying either the processing conditions—e.g., extrusion, annealing etc.—or the composition—e.g., blending, nucleation. Highly active ethylene bridged C1-symmetric zirconocene catalysts can be used to design the material properties by varying the crystallinity of thermoplastic (elastic) polypropenes. With the new unsymmetric catalyst rac−dichloro[1−(9−fluorenyl)−2−(R,S)−(5,6−cyclopenta−2−methylinden−1−η5−yl)ethane]zirconium (IV)/MAO (1) polypropenes of variable isotacticities are accessible. The variable and thus defined use of two different sides of the catalytically active species allows the placement of single, cumulated and consecutive [rr]-triads within an isotactic polymer chain. The formation of these stereoerrors is adjusted in an arbitrary manner by the polymerization conditions temperature and monomer concentration. The mechanical properties of polypropenes produced with 1/MAO vary from tough thermoplastic to excellent elastic. Stress—strain behavior of these physically crosslinked elastomers can be designed similar to the ones of polyisoprene or partly crosslinked natural rubber.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.