Question

Ziegler – Natta catalyst is:
(A) \[Ni + TiC{l_4}\]
(B) \[RLi + SnC{l_2}\]
(C) \[{({C_2}{H_5})_3}Al + TiC{l_4}\]
(D) \[{({C_2}{H_5})_3}Al + SnC{l_4}\]

Answer 1

Hint: To answer this question, we must recall the concept of polymerization. Olefins are polymerized efficiently with high linearity and stereoselectivity in presence of Ziegler Natta catalysts.

Complete step by step solution:
We should try to remember that a typical Ziegler – Natta catalyst comprises a transition metal and an organoaluminium compound. The Ziegler-Natta catalysts include many mixtures of halides of transition metals, especially titanium, chromium, vanadium, and zirconium and also with organic derivatives of non transition metals, specifically alkyl aluminum compounds.
Traditionally this polymerization was done by radical polymerization but the problem with this technique was that the formation of undesired allylic radicals led to branched polymers. Also, radical polymerization has no control over stereochemistry. Linear unbranched polyethylene and stereo regulated polypropylene could not be produced by free radical polymerization. Thus, the invention of Ziegler – Natta catalyst successfully addressed these two problems.

Hence, the correct answer is Option (C) \[{({C_2}{H_5})_3}Al + TiC{l_4}\].

Additional information:
Among the polyethylene produced by Ziegler – Natta catalyst, there are three major classes: high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and ultra-high molecular weight polyethylene (UHMWPE). HDPE, a linear homopolymer, is widely applied in garbage containers, detergent bottles and water pipes due to its high tensile strength.

Note: We should note, Ziegler – Natta catalysts are effective for polymerization of ethylene and propylene but not in case of disubstituted double bonds. They also do not work when the substrate is acrylate.