Synthesis and characterization of butadiene-1,3 and octene-1 copolymer prepared by a Ziegler-Natta catalyst based on neodymium
The aim of this work is to evaluate the influence of octene-1 incorporation in the polybutadiene chain on the polymerization reaction and polymer characteristics. Thus, copolymerization of butadiene-1,3 with octene-1 using a Ziegler-Natta ternary catalyst based on neodymium was performed. The weight ratios of butadiene-1,3/α-olefin 100/0, 99/1, 97/3, 95/5, 90/10, 80/20 and 70/30 were evaluated. The copolymers were characterized by size exclusion chromatography (SEC), infrared spectroscopy (FTIR) and thermogravimetric analysis (TG). The results showed that the degradation temperature (Tmax) was not affected by the addition of alpha-olefin, while the thermal behavior has undergone significant changes. The polymer microstructure was not influenced by the increasing of octene-1 content. However, a tendency to molecular mass increase was observed with the increasing of octene-1 content. It was also observed a trend in reduction of the polymerization conversion as the octene-1 content increased.
The effect of the comonomer on the copolymerization of ethylene with long chain α-olefins using Ziegler–Natta catalysts supported on MgCl2(THF)2
Abstract The effect of the type of the comonomer (1-pentene, 1-hexene, 1-octene, 1-decene and 1-dodecene) on the copolymerization of ethylene with α-olefin over vanadium (VOCl3 and VCl4) and titanium (TiCl4) catalysts supported on MgCl2(THF)2 and activated by Et2AlCl was studied. The results show that the introduction of a longer α-olefin in the ethylene polymerization feed depresses the catalytic activity of all investigated catalysts. The catalyst activity does not depend on the type of the comonomer applied but changes with the comonomer concentration in the feed. The incorporation of α-olefin in the polymer chain was found to be dependent on the type and concentration of the comonomer in the feed as well as the type of catalyst. The incorporation of α-olefin increases with the increase of the comonomer concentration in the polymerization feed and the comonomer reactivity decreases with the increase of the size of the α-olefin chain, especially in the case of comonomers longer than octene. It should be stressed, however, that both vanadium catalysts clearly demonstrate higher activity in the copolymerization process than their titanium counterpart and also produce copolymers with higher comonomer content. The density, crystallinity and melting temperature of the copolymers decrease with increase of the amount of the comonomer incorporated, but the type of the comonomer does not have a strong influence on these properties.
Crystal structure of the trigonal form of isotactic polypropylene as an example of density-driven polymer structure.
Propene-hexene copolymers crystallize in a new polymorphic form of isotactic polypropylene when the concentration of hexene is higher than nearly 10-15 mol %. The hexene units are included in the crystals, inducing an increase of density that allows crystallization of 3-fold helical chains in a trigonal unit cell according to the space group R3c or Rc, where the helical symmetry of the chains is maintained in the crystal lattice. The structure of this new form is similar to those of isotactic polybutene and polystyrene and does not crystallize in polypropylene homopolymer because it would have too low density. The crystal structure of isotactic polypropylene is therefore no longer an exception to the principles of polymer crystallography, but the new structure represents the fulfillment of these principles and indicates that the packing of polymer molecules is mainly driven by density.