Olefin polymerization Ziegler-Natta process

Under the reaction conditions employed, the oligomerization is living the aluminium is removed from the chain in a separate process step [2]. Further research on the Aufbau reaction led to the discovery of transition metal catalyzed olefin polymerization (Ziegler-Natta catalysis) [3]. 

The coordination polymerization of ethylene and a-olefins with Ziegler-Natta catalysts involves, in general, many elementary reactions, such as initiation (formation of active centers), chain propagation, chain transfers and chain terminations. The length of growing polyolefin chains is limited by the chain-terminating processes, as schematically represented (for ethylene) by 21,49 51)... 

Olig omerization and Polymerization. Siace an aHyl radical is stable, linear a-olefins are not readily polymerized by free-radical processes such as those employed ia the polymerization of styrene. However, ia the presence of Ziegler-Natta catalysts, these a-olefins can be smoothly converted to copolymers of various descriptions. Addition of higher olefins during polymerization of ethylene is commonly practiced to yield finished polymers with improved physical characteristics. 

Ziegler-Natta polymerization is used extensively for the polymerization of simple olefins (such as ethylene, propene, and 1-butene) and is the focus of much academic attention, as even small improvements to a commercial process operated on... 

The study of catalytic polymerization of olefins performed up to the present time is certain to hold a particular influence over the progress of the concepts of the coordination mechanism of heterogeneous catalysis. With such an approach the elementary acts of catalytic reaction are considered to proceed in the coordination sphere of one ion of the transition element and, to a first approximation, the collective features of solids are not taken into account. It is not surprising that polymerization by Ziegler-Natta catalysts is often considered together with the processes of homogeneous catalysis. 

In the propagation process of Ziegler-Natta polymerization, the insertion of olefin into a metal-carbon bond is the most important basic step, but many questions concerning to this process remained unanswered for a long time. 

Natta A process for polymerizing propylene and other higher olefins, catalyzed by crystalline titanium trichloride and an alkyl aluminum compound such as triethyl aluminum. The polymer can exhibit various types of stereoregularity, depending on the catalyst and the conditions. Invented in 1954 by G. Natta at the Istituto de Chimica Industrial del Politecnico di Milano, Italy, and commercialized in 1957. Now used widely, worldwide. See also Ziegler, Ziegler-Natta. 

Ziegler-Natta Also called Z-N. A general name for the family of olefin polymerization processes invented by K. Ziegler and G. Natta in the 1950s. Ziegler and Natta were jointly awarded the Nobel Prize for Chemistry in 1963 for their discoveries. See Natta, Ziegler (1). 

Brookhart and coworkers [1] have recently developed Ni(II) and Pd(II) bis-imine based catalysts of the type (ArN=C(R)-C(R)=NAr)M-CH3+ (la of Figure 1) that are promising alternatives to both Ziegler-Natta systems and metallocene catalysts for olefin polymerization. Traditionally, such late metal catalysts are found to produce dimers or extremely low molecular weight oligomers due to the favorability of the P-elimination chain termination process [2],... 

In the Unipol process of olefine polymerization 0.1 ixm particles of Ziegler Natta catalyst are... 

The polymerization of a-olefins, promoted by homogeneous Ziegler-Natta catalysts based on bis(cyclopentadienyl)titanium(IV) or analogous zirconium compounds and aluminum alkyls, occurs simultaneously with a series of other reactions that greatly complicate the kinetic interpretation of the polymerization process (see Scheme 3). 

---