Industrial polyolefin processes

Since their discovery over a decade ago, late transition metal a-diimine polymerization catalysts have offered new opportunities in the development of novel materials. The Ni(II) catalysts are highly active and attractive for industrial polyolefin production, while the Pd(II) catalysts exhibit unparalleled functional group tolerance and a propensity to form unusually branched polymers from simple monomers. Much of the success of these catalysts derives from the properties of the a-diimine ligands, whose steric bulk is necessary to accelerate the insertion process and inhibit chain transfer. 

Although much work on the development of transition metal catalysts for the co-polymerization of hydrocarbon and polar monomers has been reported (particularly in the patent literature), so far no effective means seems to exist for directly incorporating functionality into a polyolefin chain by using an industrially feasible process. With respect to polar monomer co-polymerization, Jordan et and Boone et al thoroughly investigated ethylene and vinyl... 

A considerable number of reports regarding the formation of compounds that may represent a health hazard are related to the formation of polycyclic aromatic hydrocarbons (PAHs) during industrial pyrolysis processes (recycling of waste, incineration, etc.). This interest is particularly geared toward the study of polyolefins pyrolysis and synthetic and natural rubber pyrolysis. The formation of PAHs during polyethylene pyrolysis has been reported frequently in literature [6, 12] and is further discussed in Section 6.1. The formation of PAHs during tire pyrolysis is also of considerable concern. The concentrations of some components in the oils generated from the pyrolysis of used tires as a function of temperature are indicated in Table 5.3 1 [13]. 

Rubber matrices have commonly been used as a second phase to improve the toughness of brittle thermoplastic materials, such as polypropylene and polyethylene. These systems, commonly referred to as polyolefin thermoplastic elastomers (TPOs), are a special class of thermoplastic elastomers that combine the processing characteristic of plastics at elevated temperatures with the physical properties of conventional elastomers at service temperature, playing an increasingly important role in the polymer material industry. Polyolefin blends attract additional interest due to the possibility of recycling plastic wastes, avoiding the complex and expensive processes of separation of the different components. 

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.

Melt Intercalation Environmentally benign use of polymers not suited for other processes compatible with industrial polymer processes. Limited applications to polyolefins, who represent the majority of used polymers. 

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