title: End Groups of Functionalized Siloxane Oligomers Direct Block-Copolymeric or Liquid-Crystalline Self-Assembly Behavior.
abstract: Monodisperse oligodimethylsiloxanes end-functionalized with the hydrogen-bonding ureidopyrimidinone (UPy) motif undergo phase separation between their aromatic end groups and dimethylsiloxane midblocks to form ordered nanostructures with domain spacings of <5 nm. The self-assembly behavior of these well-defined oligomers resembles that of high degree of polymerization (N)-high block interaction parameter (χ) linear diblock copolymers despite their small size. Specifically, the phase morphology varies from lamellar to hexagonal to body-centered cubic with increasing asymmetry in molecular volume fraction. Mixing molecules with different molecular weights to give dispersity >1.13 results in disorder, showing importance of molecular monodispersity for ultrasmall ordered phase separation. In contrast, oligodimethylsiloxanes end-functionalized with an O-benzylated UPy derivative self-assemble into lamellar nanostructures regardless of volume fraction because of the strong preference of the end groups to aggregate in a planar geometry. Thus, these molecules display more classically liquid-crystalline self-assembly behavior where the lamellar bilayer thickness is determined by the siloxane midblock. Here the lamellar nanostructure is tolerant to molecular polydispersity. We show the importance of end groups in high χ-low N block molecules, where block-copolymer-like self-assembly in our UPy-functionalized oligodimethylsiloxanes relies upon the dominance of phase separation effects over directional end group aggregation.
authors.affiliation: Institute for Complex Molecular Systems and Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology , 5600 MB Eindhoven, The Netherlands.
authors.forename: R Helen
authors.initials: RH
authors.lastname: Zha
authors.affiliation: Institute for Complex Molecular Systems and Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology , 5600 MB Eindhoven, The Netherlands.
authors.forename: Bas F M
authors.initials: BF
authors.lastname: de Waal
authors.affiliation: Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University , 3584 CH Utrecht, The Netherlands.
authors.forename: Martin
authors.initials: M
authors.lastname: Lutz
authors.affiliation: Institute for Complex Molecular Systems and Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology , 5600 MB Eindhoven, The Netherlands.
authors.forename: Abraham J P
authors.initials: AJ
authors.lastname: Teunissen
authors.affiliation: Institute for Complex Molecular Systems and Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology , 5600 MB Eindhoven, The Netherlands.
authors.forename: E W
authors.initials: EW
authors.lastname: Meijer