Metallocene-based polyolefin processes

Knuuttila H, Lehtinen A, Salminen H (2000) Metallocene catalyst technology in a bimodal polymerization process. In Scheirs J, Kaminsky W (eds) Metallocene-based polyolefins. Wiley, Hoboken, pp 365-378... 

Metallocene-based polyolefin alloys, blends and compounds, an emerging class of novel plastic products, offer an unique combination of performance properties. In polymer blending and/or alloying, often dissimilar polymers are physically mixed (com-patibilized) and/or chemically reacted (reactive extrusion processing). 

Metallocene-based polyolefins blends can be developed which combine the performance characteristics of rubber, while maintaining a plastic s inherent ease of processibility. The extremely narrow molecular weight distributions and uniform comonomer composition result in improved and consistent physical properties. 

As a result of the controlled long-chain branching in otherwise linear polymers, the processability of these resins is claimed to be significantly enhanced compared to the standard LLDPE and EP rubber materials. Envircmmental stress crack resistance of metallocene polyolefin is also claimed to be significantly better. A wide range of densities (0.86-0.93), flexural modulus (10-100 MPa), melting points (60-120 °C), and melt flow index (0.5-125) is available in the commercial metallocene-based ethylene copolymers. 

Figure 6. The spectrum of iPP shows only one methyl group signal typical for the meso (mmmm) pentad, whereas the racemic (rrrr) pentad is typical for syndiotactic polypropylene (sPP). The remarkable history of polyolefins and the development of the stereoselective 1-olefin polymerization is described in reviews by Pino and Miilhaupt [5], covering the first 25 years, and by Brintzinger et al. [6, 7], covering modem aspects of metallocene-based propylene polymerizations. PP technology is the subject of several books [8-11] including the chapter Industrial polymerization processes in this book.

Metallocene/MAO and other single-site catalysts allow the synthesis of tailored polyolefin structures in a way that was impossible in previous years. The known dependence of the kind of metallocene-based polymer on the catalyst structure allows the modeling of the reaction kinetics and the polymerization process... 

Cocatalysts for metallocene-based olefin polymerization catalyst systems Metallocenes supported on ion exchange resins Olefin polymerization catalysts Process and a catalyst for preventing reactor fouling Supported metallocene catalysts for the production of polyolefins... 

With the exception of LDPE, polyolefins like other polyethylenes and polypropylene, which represent the largest amount of vinyl-type polymers produced in the world, are neither synthesized by radical nor by classical ionic polymerisation processes. Different types of polymerisation catalysts are in use for these purposes. The Cr-based Phillips catalyst, Ziegler-Natta type catalysts, metallocene or other more recently discovered catalysts, including late transition metal catalysts, are all characterized by their propagation step where the olefin monomer inserts into a carbon-transition metal link. ... 

Based on an early process discovered by Natta in the 1950s, soluble transition metal catalysts like metallocenes were developed mainly in the 1950s as initiators for polyolefin syntheses. Others are still now under investigation, like the so-called LTM (for "late transition metal") catalysts. Metallocenes seem... 

A review is presented of the nitrogen autoclave process for the manufacture of crosslinked polyolefin foams. Process and product developments over the last few years are summarised and future possibilities are described. Process developments include use of higher temperatures and pressures to produce foams having densities as low as 10 kg/cub.m. Product developments include foams based on HDPE/LDPE blends, propylene copolymers and metallocene-catalysed ethylene copolymers. The structure and properties of these foams are compared with those of foams produced by alternative processes. 5 refs. 

Symyx-Dow A process for making polyolefins using a hafnium-based metallocene catalyst that had been identified by the Symyx combinatorial method. Not commercialized in 2003. 

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