Synthesis of functionalized polymer brushes part III: amino brushes

摘要

Surface-attached polymer monolayers with controlled structures and thicknesses are accessible via surface-initiated polymerization using monolayers of azo-initiators. We have also shown that a two step strategy for the preparation of such functional surface architectures that stars out with the decoration of the surfaces with brushes carrying so-called active ester moieties [e.g. N-hydroxysuccinimide (NHS) groups] which can subsequently the transformed to the desired function via aminolysis reactions offers some advantages especially if functional monomers are not available in sufficient amounts or are not compatible with the radical nature of the polymerization. Even though this approach proved to be successful for the generation of functional polymer brushes it is limited to those molecules that are available as amines. Especially among the biologically relevant functions like for example biotin and biotin-derived species that one might want to introduce many of the molecules that would have to be used are more readily available as acids (or active esters) rather than amines or offer both functions like peptides. From this point of view it appears to be desirable to also star out with polymer brushes that carry amino functions to which then functional molecules with NHS anchors can be attached. Amino functionalized polymer brushes prepared by our approach, however, are not directly accessible because the amino groups would undergo electron transfer reactions with the growing chain ends rendering a successful radical polymerization impossible. Due to this problem we decided to investigate as to whether amino functional polymer brushes can be synthesized from protected monomers that deliver the amino function after a subsequent deprotection step. The focus of the work described in this contribution was put on a thorough investigation of the surface-initiated polymerization and the subsequent deprotection step because these two processes need to be well controllable if the resulting monolayers are to be used for a final incorporation of functional groups into the system.