[Meloentje]

Hi, does anyone of you have soms experience with a RAFT-polymerisation? Could someone please explain me how this reaction ensures polymers with a very small PDI? i don't quiz understand how all the growing chains can react at the same speed, which leads to polymers of the same length.

[Hunter2]

http://en.wikipedia.org/wiki/Reversible_addition%E2%88%92fragmentation_chain-transfer_polymerization

http://www.google.fr/search?q=RAFT+polymerisation&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

[Meloentje]

http://en.wikipedia.org/wiki/Reversible_addition%E2%88%92fragmentation_chain-transfer_polymerization

http://www.google.fr/search?q=RAFT+polymerisation&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

Still not clear...

[opsomath]

Why don't you start by asking a specific question?

[Meloentje]

Why don't you start by asking a specific question?

Well, this is how I see it. At a certain temperature all the initiator molecules fall apart and become radicals. The radicals just react with 1 monomer? Why not directly 2 or 3 or more? Becausenthe RAFT agent stabilizes them or what? And why does the R group come free instead of the growing chain just added to the RAFT?

I don't understand how all growing chains react at the Same speed giving chains with equal length eventually...

[opsomath]

RAFT is a specific example of a controlled radical polymerization. Others are NMP (nitroxide mediated radical pzn) and ATRP (atom transfer radical polymerization).

All of them have one thing in common: the radical is formed in an equilibrium which is very unfavorable, producing only tiny concentrations of radical at a time. This is in contrast to, for instance, the pzn of polystyrene by a peroxide, where radicals form fast and uncontrolled.

The higher the concentration of radicals, the greater the chance that two of them will react with each other (coupling termination) or with some contaminant or the side of the vessel, rather than with a molecule of monomer. (propagation).

So the short version is that RAFT works by keeping the concentration of radicals very low so that the main thing that happens is propagation, and termination or other reactions are suppressed.