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Grafting through: Mostly grafting to with a little extra spin

Polymers are made from monomers. If some of the monomers are attached to a surface these monomers may be incorporated during chain growth. This will tether this chain to the surface. The strategy is known for decades but the mechanism and the influence of selected reaction parameters remained less well understood. We found that the reaction has some rather interesting features. One of them can be summarized with five words: You know what you get.

The process in general has two steps: A growing chain must capture the immobilized double bond - which basically is a grafting-to step - and then the chain continues growth away from the surface. Our lab slang called that "grafting in between" because of this mixed status. We found that it is not so "in between" as this simple thought suggests. The overall reaction is much closer to grafting to because it becomes harder and harder for new growing chains to get to the surface. Still the layers do get a bit thicker and growth never really levels off because small chains may still diffuse to the surface and bind at later stages.

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Nevertheless, the process is mostly self-limiting and as such not very sensitive to batch-to-batch variations or errors. You more or less get the same layer thickness, regardless of reaction parameters like temperature, concentrations, solvents and even reaction time. You know what you get.

Michael Henze, Daniel Mädge, Oswald Prucker, and Jürgen Rühe
“Grafting Through”: Mechanistic Aspects of Radical Polymerization Reactions with Surface-Attached Monomers
Macromolecules 2014, 47 (ASAP publication)
DOI: 10.1021/ma402607d

 

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