[Machuu]

Hi,

I read recently about the synthesis of star polymers using macromonomers like poly(butyl acrylate) and small amount of initiator and divinyl crosslinker. After that I started to wonder how it's possible to initiate a polymerization. How generated radical (for example from EBiB) can react with poly(BA)? Does poly(BA) have double bonds as terminal groups? Till today I was thinking that polymerization of butyl acrylate ends by combination of two macroradicals and only small % of macroradicals ends by disproportionation producing an unsaturaded group.

[wildfyr]

Using Ethyl bromoisobutyrate is indicative of a polymerization done using ATRP to make the macromonomer. In a normal free radical polymerization the terminal atom is almost always hydrogen, taken either by disproportionation, backbiting or stolen from the solvent. However in a controlled ATRP polymerization, the terminal atom on a linear polymer is a chlorine or bromine. This can be leveraged as a reactive handle to make a star polymer. If you want to share the paper I can confirm my thoughts, since I'm just guessing. It's also possible that a macromonomer was made by RAFT.

[Machuu]

My post refers to this publication : https://pubs.acs.org/doi/10.1021/ja066964t

Scheme 1 shows a macromonomer with terminal double bond that's why I started to wonder. This publication clearly distinguishes macroinitiators method and macromonomers method.

[wildfyr]

Ok, its a Matyjaszewski paper, so it definitely includes ATRP! I think the Figure 1 you are referring to is kind of misleading, it doesn't differentiate between individual reaction steps, and concepts that are happening within a single pot.

So I think I was essentially right. What they do is make a macroinitiator with ATRP of polyBA, it has a terminal bromine (polyBA-Br). Then they take that purified polymer and put it in an ATRP reaction with divinyl benzene. The divinyl benzene will react a little with itself, and also with the polyBA-Br. This creates a sort of hairy looking star polymer, with some of the vinyls from the divinyl benzene and some ethyl benzene with terminal Brs present because they stop it before full conversion.

The one using the PEGMA (aka PEO methacrylate) macromonomer is simply a monomer that has a polymeric side chain. Its made by esterifying methacrylic acid (or methacryloyl chloride) with OH terminated PEG. Figure 1 bottom half actually has a mistake, they don't use divinyl benzene, they use EDGMA (a bis-methacrylate). This time its just ATRP of a large monomer methacrylate with a bis functional methacrylate. Calling PEGMA a macromonomer is a little cheap, you can buy decent MW PEGMA off the shelf. They should have at least drawn it as a methacrylate, not just a terminal alkene.

The supporting info often contains this kind of nitty gritty, its where I went to figure this out.