Tunable Surface Properties from Sequence-Specific Polypeptoid-Polystyrene Block Copolymer Thin Films

Tunability of polymer surface properties depends crucially on both the chemical composition of the polymer and the physics of the chains (e.g., surface segregation, chain shape, etc.). Polypeptoids, which are non-natural biomimetic polymers based on an N-substituted glycine backbone, provide a flexible model system in which monomer sequence, chain shape, and self-assembled structure can easily be controlled to understand their influence on surface properties. We demonstrate the influence of the amount and sequence of hydrophobic monomers in a predominantly hydrophilic peptoid chain on the surface properties of a hybrid block copolymer, poly(peptoid-b-styrene). Just three fluorinated groups in peptoid sequences consisting of up to 45 hydrophilic monomers in length were needed to lower the surface energy of the peptoid and allow for its maximal surface segregation. Positioning these fluorinated groups in the middle of a chain as opposed to the chain ends resulted in a change in chain conformation at the surface as evidenced by near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Surface reconstruction of polymers containing only three fluorinated monomers occurred within seconds but could be slowed by an order of magnitude when five fluorinated monomers were incorporated.