¿Qué me indica el número atómico (Z)?

It refers to the category of catalyst that are used in the polymerization of ole-fins (alkenes ) . It is actually a mixture of titanium tetra chloride chloride and alkyl derivative of Aluminium .

Explanation:

Polymerization : The process by which small units unite to form a giant molecule that is a polymer .

The chemical reactions often takes place in presence of catalyst .Catalyst is the substance that affects the rate of reaction without undergoing any change in itself .It might be rate enhancer or inhibitor .But mostly they are employed to increase the rate of reaction like Ziegler catalyst is used in polymerization of ethene .

The ethene is polymerized as shown :

C₂H₄ > --{---CH-CH- }n

   ( Zeigler Nata catalyst )