Macromolecular ligands have been widely used in the past two decades with the objective of preparing structurally defined heterogeneous catalysts from soluble organometallic complexes. This activity has been largely reconsidered and focused on few specific systems. In this connection the present paper reviews recent data concerning the preparation of macromolecular metal complexes derived from transition metals which can produce active catalytic complexes for olefin polymerization and oligomerization and comparison is made about the suitability of both organic resins (crosslinked polystyrene) and inorganic materials (silica, alumina and zeolites).
The recovery of plastic waste may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins with copolymer additives to improve the mechanical properties and increase the useful life of the blends. The values obtained for the mechanical and thermal properties for polypropylene (PP) with recycled high density polyethylene (HDPE) show that it is possible to use recycled HDPE up to 30% w/w. The properties and applications are similar to those obtained with PP alone, thereby reducing the cost of the raw material. The addition of the compatibilizer at 5% represents the optimal concentration for improving the final properties of the finished product. Analysis of the mechanical and thermal behavior of the low density polyethylene (LDPE) with recycled HDPE blends lead us to conclude that it is possible to use recycled HDPE because the properties of the finished product are thereby enhanced.
This paper investigates the homo- and copolymerization of styrene with p-methylstyrene, m-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene and 2,4,6-trimethylstyrene using a Cp*TiCl3 (Cp: cyclopentadienyl) semimetallocene catalyst activated with methylaluminoxane. Syndiotactic homo- and copolymers were obtained only for the monosubstituted monomers. For the di- or trisubstituted monomers, reduced reactivities, stereoregularities, and degrees of polymerization were obtained with respect to the monosubstituted monomers. More specifically, the homopolymerization of 2,5-dimethylstyrene and 2,4,6-trimethylstyrene and their copolymerization with styrene was inhibited. The reason for this are combined steric and inductive effects. The presence of methyl groups in para position seems to inhibit crystallization of the syndiotactic polymers. In contrast, crystallinity was evidenced in the materials produced in the presence of m-methyl substituted monomers.
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