Polymer grafting via ATRP initiated from macroinitiator synthesized on surface.

Macromolecular anchoring layer approach was used for preparation of an effective macroinitiator for the synthesis of grafted polymer layers by atom transfer radical polymerization (ATRP) initiated from the surface. For the initial surface modification, a thin layer of poly(glycidyl methacrylate) (PGMA) was deposited on the surface of a silicon wafer. The ATRP macroinitiator was synthesized on the substrate surface by the reaction between epoxy groups of PGMA and carboxy functionality of bromoacetic acid (BAA). Variation of the time and temperature of the BAA deposition as well as PGMA layer thickness allowed control over the amount of BAA attached to the surface. The PGMA anchoring layer allowed the achievement of initiator surface density significantly higher than that reported for a self-assembled monolayer of ATRP initiators. Polymer brushes were synthesized on the PGMA/BAA-modified substrates by ATRP. Different surface concentrations of BAA were used in our grafting experiments to acquire knowledge about the relationship between the amount of initiator anchored to the surface through PGMA and the rate of the grafted layer formation. The increase in the surface density of the initiating moieties led to the increase in the grafting rate. However, a cutoff initiator concentration beyond which no increase of the thickness of the grafted layer was observed. From comparison between the surface densities of the initiator and the attached polymer it was determined that the efficiency of the initiation from the surface was on the level of 5-15%.