[andy719]

Hi all,

I have done an experiment of cationic polymerization of styrene by using CH2Cl2 as the initiator.
However, I am quite confused about the mechamisn of the use of CH2Cl2. Have I made mistake in the first step? Also, does the polystyrene carry chloride atoms in this situation? Thank you so much.

[kriggy]

Isnt it just a solvent?

[orgopete]

I don't think the CH2Cl2-AlCl3 complex will disassociate as shown in your scheme. AlCl3 itself can associate with double bond of styrene and catalyze the polymerization. You may then find its addition might be reversed so aluminum is not part of the product.

[andy719]

I think it is a little bit strange too but I have only added styrene, dichloromethane and AlCl3 as the reagents. So CH2Cl2 should be the reagent to form a cationic species for the polymerization.

In addition, the experiment said it is a cationic polymerization of styrene and if CH3Cl is used, the mechanism is sensible.
But I am not pretty sure how CH2Cl2 can form a cation with AlCl3.

[kriggy]

No its solvent. The raction goes like this IMO: (the charges are just for ilustration, I cant draw better )

[orgopete]

I did mean to have a bond to the aluminum. That would give a tetravalent aluminum, which would accomplish the same reaction. You might consider what happens to the aluminum if treated with water or acid. Here, the negative charge is a hint.

[andy719]

So based on the above replies, is this scheme correct? Thanks again for answering so many questions.