EndGroups of Functionalized Siloxane Oligomers Direct Block-Copolymericor Liquid-Crystalline Self-Assembly Behavior

摘要

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 moreclassically liquid-crystalline self-assembly behavior where the lamellarbilayer thickness is determined by the siloxane midblock. Here thelamellar nanostructure is tolerant to molecular polydispersity. Weshow the importance of end groups in high χ–low N block molecules, where block-copolymer-like self-assemblyin our UPy-functionalized oligodimethylsiloxanes relies upon the dominanceof phase separation effects over directional end group aggregation.