How do alkenes react to form polymers in polymerisation?

1 Answer
Feb 4, 2017

Typically ethylene inserts into a ""^(+)M-R bond, where the R group starts as methyl.......

Explanation:

The typical olefin polymerization reaction starts with a metal dimethyl species, L_2M(CH_3)_2, where (i) M is a metal such as titanium or zirconium, and (ii) L is some ligand that stabilizes and solubilizes the metal centre.

Addition of a Lewis acid abstracts one of the methyl groups to yield a species conceived to be L_2M^(+)(CH_3):

L_2M(CH_3)_2 + "aluminum reagent"rarrL_2M^(+)(CH_3) + "methylated aluminium reagent"

Ethylene can bind to the cationic metal centre:

L_2M^(+)(CH_3)+H_2"C=C"H_2rarrL_2M^(+)(CH_3)(eta^2-H_2"C=C"H_2)

The methyl group bound to the metal centre can migrate to the eta^2-"bound" olefin to give a propyl group. And such insertion generates an open coordination site on the metal centre, to which another ethylene can bind, and this reinserts into the M-"alkyl" residue. Long chain alkyl residues, polyethylenes, can be built up this way.

This will be much better explained in your given text.