Grafting of Homo- and Block Co-polypeptides on Solid Substrates by an Improved Surface-Initiated Vapor Deposition Polymerization

Abstract

Grafting of poly(γ-benzyl l-glutamate) (PBLG) on silicon native oxide surfaces by the surface-initiated vapor deposition polymerization (SI-VDP) method was first demonstrated by Chang and Frank (Langmuir 1998, 14, 326). In the current study, we have further improved this method by redesigning the reaction chamber and optimizing the reaction parameters, including monomer concentration, substrate temperature, and reaction time. Through the process optimization, we can fabricate end-grafted α-helical PBLG films with tunable thicknesses from a few nanometers to hundreds of nanometers in less than 1 h of reaction time. For example, a 187 nm PBLG grafted film was synthesized at 95 °C monomer evaporating temperature, 75 °C substrate temperature, and 0.1 Pa in 30 min. In this study, the SI-VDP process was also applied to synthesize other homo-polypeptide and block co-polypeptide thin film systems. The successful syntheses of poly(γ-methyl l-glutamate) (PMLG), poly-l-phenylalanine (PLPA), poly(β-benzyl l-aspartate) (PBLA), poly(Nε-carbobenzyloxy l-lysine) (PCBL), PLPA-b-PBLG, and PBLG-b-PCBL grafted films were demonstrated. Their chemical compositions, secondary structures, thicknesses, refractive indices, and water contact angles were characterized by Fourier transform infrared spectroscopy (FTIR), ellipsometry, and contact angle goniometry, respectively.