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Author: Subject: Bromination of polystyrene
steadyhand
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[*] posted on 29-4-2022 at 12:57
Bromination of polystyrene


I'd like to place active sites on a polystyrene substrate, preferably para to the backbone. My idea is to form a polystyrene as a thin film onto a physical carrier that I've previously activated in some manner. Then I want a controllable percentage of sites on the exposed aryls to get a functional group I can tack things on to. Br comes to mind.

This would most likely stack up as a glass base, a lipid layer about 1um thick, then polystyrene somewhat thinner than that with the aryls exposed and activated. The lipid layer might be tacked to the glass by esters (stearic acid comes to mind), and to the polystyrene the same way. This stackup allows me to work in polar media on the chemistry side with a protected, flexible lipid layer over a sensor covered by a glass plate.

I got the idea from a paper on making magnetic particles shrouded in polystyrene with halogen sites they then used to attach their particular junk onto. In their case they used pre-halogenated styrene and then polymerized PVA, some cross-linker, styrene monomer, and the desired proportion of 4-chlorostyrene. Problem is, that 4-cs is 'spensive, and probably a pain to procure. Also, I think the PVA leaves a lot of -OH groups?

I would like: components of a polymer system including PVA-ish chains, cross-linking agents, and styrene monomer, all readily available. Anyone know of a good source for the amateur?

THEN, I would like a means to add a functional group para to the backbone. My first thought is the NBS I made (yay, no more dealing with Br2!). As I read it, I need a weak Lewis acid since a strong one (AlCl3?) would attack the backbone. A paper I read on this mentions Antimony trichloride, but is there something cheaper or makeable? Having trouble determining what makes for a good weak Lewis acid.

magnetic polystyrene: https://www.researchgate.net/publication/331752620_Highly_Ma...

NBS-polystyrene:
https://data.epo.org/publication-server/document?iDocId=3555...
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aab18011
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[*] posted on 29-4-2022 at 22:38


Correct me if im wrong, but wont NBS brominate the alkyl group of the benzene? The hydrogen of the -CH2- in the PhCH2-R would get attacked. Or thats what I thought.



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alchemizt
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[*] posted on 30-4-2022 at 10:11


Quote: Originally posted by aab18011  
Correct me if im wrong, but wont NBS brominate the alkyl group of the benzene? The hydrogen of the -CH2- in the PhCH2-R would get attacked. Or thats what I thought.


You can make it more selective towards aryl bromination by doing the reaction in the dark. I beleive its because the benzylic brominations happens through a free radical intermediary
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steadyhand
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[*] posted on 30-4-2022 at 10:26


From what I've read, using an oxidizer such as benzoyl peroxide and NBS will attack the benzylic carbons of the backbone as you point out. (BTW, I think you mean ArCH2-R since there's no hydroxyl)
But with a Lewis acid NBS can brominate activated aromatics. In this case the -R substituent is a mild activator? I read this on https://www.masterorganicchemistry.com/2011/06/10/reagent-fr...

From the second doc, "The catalyst is a weak Lewis acid halogenation catalyst, preferably antimony trichloride or antimony tribromide. By "weak" it is understood to mean that the catalyst is incapable of catalyzing a Friedel-Crafts alkylation reaction or, in this specific system, the reaction of a halogenated hydrocarbon with an aromatic substrate such as polystyrene. In the case of a polyhalogenated solvent such a reaction would result in an undesirable crosslinking reaction."
They are using BrCl or Br2 as the agent.

OTOH, In looking at https://www.organic-chemistry.org/chemicals/oxidations/n-bro...
I find several Ar-X methods using NBS with a) a weak Lewis acid, b) TBAB, c) H2SO4. In cases a) and b) it is for activated aryls, c) is for de-activated aryls.

There is the possibility of brominating the ring of styrene before forming the plastic, but I haven't found a method.

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