title: Elucidation of the structure of poly(γ-benzyl-l-glutamate) nanofibers and gel networks in a helicogenic solvent.
abstract: The synthesis, characterization, self-assembly, and gel formation of poly(γ-benzyl-l-glutamate) (PBLG) in a molecular weight range from ca. 7,000-100,000 g/mol and with narrow molecular weight distribution are described. The PBLG is synthesized by the nickel-mediated ring-opening polymerization and is characterized by size-exclusion chromatography coupled with multiple-angle laser light scattering, NMR, and Fourier transform infrared spectroscopy. The self-assembly and thermoreversible gel formation in the helicogenic solvent toluene is investigated by transmission electron microscopy, atomic force microscopy, small-angle X-ray scattering, and synchrotron powder X-ray diffraction. At concentrations significantly below the minimum gelation concentration, spherical aggregates are observed. At higher concentrations, gels are formed, which show a 3D network structure composed of nanofibers. The proposed self-assembly mechanism is based on a distorted hexagonal packing of PBLG helices parallel to the axis of the nanofiber. The gel network forms due to branching and rejoining of bundles of PBLG nanofibers. The network exhibits uniform domains with a length of 200 ± 42 nm composed of densely packed PBLG helices.
authors.affiliation: Institute for Technical Chemistry, Braunschweig University of Technology, Hans-Sommer-Straße 10, 38106 Braunschweig, Germany.
authors.forename: Ansgar
authors.initials: A
authors.lastname: Niehoff
authors.forename: Alexandre
authors.initials: A
authors.lastname: Mantion
authors.forename: Richard
authors.initials: R
authors.lastname: McAloney
authors.forename: Alexandra
authors.initials: A
authors.lastname: Huber
authors.forename: Jana
authors.initials: J
authors.lastname: Falkenhagen
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: Goh
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Thünemann
authors.forename: Mitchell A
authors.initials: MA
authors.lastname: Winnik
authors.forename: Henning
authors.initials: H
authors.lastname: Menzel
keywords: Nanofiber; Nickel-mediated NCA polymerization; Physical/supramolecular organogel; Poly(γ-benzyl-l-glutamate) (PBLG); Self-assembly; Thermoreversible gel formation; α-Helix