ABSTRACT
An enormous interest in the synthesis of polyolefins has been created in recent years due to the discovery of a new class of catalysts called metallocenes [1-3] . These catalysts produce new polymers, such as syndiotactic polypropylene, and cycloolefin copolymers, or can be used in the field of already existing polyolefins, such as linear low-density polyethylene (LLDPE), high-density polyethylene, isotactic polypropylene, and ethylenepropylene rubber. The most remarkable feature of these emerging catalyst systems is the fact that all metallocene sites produce polymer chains with virtually the same architecture (Fig. 1) as compared with the different structures of polymer chains obtained with traditional multiple site heterogeneous catalysts. This characteristic opens up many possibilities for producing tailored polyolefin materials with controlled molecular weights, consistent comonomer contents, desired molecular weight and chain branching distribution, and control tacticity pattern, etc. New molecular architecture of homogeneous polymer molecules coupled with the compatability of metallocene systems with existing polyolefin production processes has led to faster commercialization of metallocene-based polyolefins (Table 1) [4] . To date, most efforts have been devoted to catalyst dev~l opment and their evaluation for polyolefin synthesis. Presently, attention has also been focused on other aspects of the new generation ofpolyolefin materials, such as processability and additive package for various end use applications [5] . Most early applications have been in speciality polymer markets where value-added and higher priced new polyolefins can compete. The met~llo cene-based polyolefins are expected to compete m a
broader thermoplastic market as more understanding of the different commercially significant aspects are realized.
