Effect of solvents and temperature on the conformation of poly(beta-benzyl-L-aspartate) brushes

We report on the synthesis and characterization of end-tethering polypeptide monolayers based on poly(beta-benzyl-L-aspartate) (PBLA) homopolymer and PBLA-b-poly(gamma-benzyl-L-glutamate) block copolymer. The homopolypeptide and copolypeptide brushes were fabricated by the sequential, surface-initiated vapor deposition polymerization of the N-carboxyanhydride of beta-benzyl-L-aspartate or gamma-benzyl-L-glutamate, yielding 80-nm-thick, chemically grafted films after 30 min of reaction time. Both Fourier transform infrared spectrometry and circular dichroism showed that the polypeptide brushes could be reversibly and repeatedly switched between left-handed and right-handed alpha-helical structures in response to solvent vapor exposure or permanently converted to a beta-sheet structure when heated to 160 degrees C in air. The facile, in vacuo manufacturability and the robustness of the films of PBLA-based brushes could allow them to be incorporated as active components for biosensing and nanofabricated devices.