Hongbing Pan

Synthesis and sub-10 nm supramolecular self-assembly of a nanohybrid with a polynorbornene main chain and side-chain POSS moieties

A polynorbornene-based mesogen-jacketed liquid crystalline polymer (MJLCP) containing polyhedral oligomeric silsesquioxane (POSS) in the side chain, PNb10POSS, was synthesized through ring-opening metathesis polymerization. The chemical structure of the monomer was confirmed by 1H/13C NMR, high-resolution mass spectrometry, and elemental analysis. Molecular characterizations on the polymer were performed with 1H NMR, gel permeation chromatography, and thermogravimetric analysis. The phase behavior of this new organic–inorganic hybrid polymer was investigated by differential scanning calorimetry, polarized light microscopy, one-dimensional wide-angle X-ray scattering, synchrotron-radiation small-angle X-ray scattering (SAXS), two-dimensional wide-angle X-ray diffraction, and high-resolution transmission electron microscopy. With the competitive self-assemblies of the two covalently connected building blocks, namely MJLCP and POSS moieties, PNb10POSS shows various phase structures including an angstrom POSS crystal (Cr), a hexagonal columnar (Colh) phase and the Cr coexisting, and the Colh phase at different temperatures. The POSS crystal has a tremendous effect on the liquid crystalline (LC) behavior of the MJLCP. The results show that the competition between the crystallization of POSS and the LC formation of the polymer as a whole results in the complex phase behavior of the MJLCP-based nanohybrid. The polymer self-assembles into an organic–inorganic hybrid inclusion complex on the sub-10 nm scale. This work provides a new approach for the design and synthesis of ordered structures constructed by self-assembly on the sub-10 nm scale.

Bulk self-assembly and ionic conductivity of a block copolymer containing an azobenzene-based liquid crystalline polymer and a poly(ionic liquid)

By combining nitroxide-mediated block copolymerization with post functionalization and ion exchange, a series of block copolymers (BCPs) containing an azobenzene-based side-chain liquid crystalline (LC) polymer and an imidazolium-containing poly(ionic liquid) (PIL) were synthesized. The LC block of the BCPs studied herein is poly(4-[12-(4-butyl-4′-oxy-azobenzene)dodecyl]oxycarbonylstyrene) (PAzo), while the PIL block is poly(4-vinylbenzylhexylimidazoliumbis(trifluoromethanesulfonyl)imide) (PIL(TFSI)). As far as we know, this is the first series of BCPs having both PIL and LC polymer blocks. In this series of BCPs, the PIL(TFSI) blocks are totally ionized, while the polymer compositions are varied. When the weight fraction of PIL(TFSI) is 29.7%, the BCP self-assembles into a hexagonally packed cylindrical (HEX) structure. For the BCP with 56.5 wt% PIL(TFSI), it self-assembles into a lamellar (LAM) structure when the PAzo block is LC; and it changes into a HEX structure when the PAzo block enters into the isotropic state, which is attributed to the more flexible interface between PIL(TFSI) and PAzo at temperatures above the clearing temperature of PAzo. When the weight fraction of PIL(TFSI) is 65.3%, the nanostructure of the BCP remains LAM during heating. The ionic conductivities of the BCP with 65.3 wt% PIL(TFSI) at 40 and 140 °C are 4.45 × 10−5 and 5.81 × 10−4 S cm−1, respectively, which indicates that the BCP can be used as a solid polymer electrolyte.

Self-Assembly and Properties of Block Copolymers Containing Mesogen-Jacketed Liquid Crystalline Polymers as Rod Blocks

Mesogen-jacketed liquid crystalline polymer (MJLCP) has attracted great attention because of its rigid conformation, facile synthesis, and structural controllability. In this feature article, the self-assembly of MJLCP-based block copolymers (BCPs) is briefly reviewed, especially the nanostructures of rod-coil diblock copolymers (diBCPs), rod-rod diBCPs, and triblock copolymers. In addition, the properties of the self-assembled BCPs are also summarized, including their applications as liquid crystalline thermoplastic elastomers and solid polymer electrolytes. The article also discusses the major challenges and future directions in the study of MJLCP-based BCPs.

Hierarchically ordered structures of disk-cube triads containing hexa-peri-hexabenzocoronene and polyhedral oligomeric silsesquioxane

Obtaining nanoscale-ordered structures is important for the development of nanotechnology. We designed and synthesized a series of disk-cube triads containing one hexa-peri-hexabenzocoronene (HBC) and two polyhedral oligomeric silsesquioxane (POSS) moieties, HBC-2POSS. The two POSS units were linked via ester or amide bonds. With the amide linkage used, the hydrogen bonding that was introduced affected the balance between the π-π interaction of HBC cores and crystallization interaction of POSS units. Hierarchically ordered structures were obtained from HBC-2POSS triads owing to the synergistic effect of multiple secondary interactions: π-π interaction, hydrogen bonding, and crystallization interaction. As organic-inorganic hybrid materials, these HBC-2POSS triads are promising candidates for templates <10 nm.

Head–Tail Asymmetry as the Determining Factor in the Formation of Polymer Cubosomes or Hexasomes in a Rod–Coil Amphiphilic Block Copolymer

The self-assembly of a rod-coil amphiphilic block copolymer (ABCP) led to Im3‾ m and Pn3‾ m polymer cubosomes and p6mm polymer hexasomes. This is the first time that these structures are observed in a rod-coil system. By varying the hydrophobic chain length, the initial concentration of the polymer solution, or the solubility parameter of the mixed solvent, head-tail asymmetry is adjusted to control the formation of polymer cubosomes or hexasomes. The formation mechanism of the polymer cubosomes was also studied. This research opens up a new way for further study of the bicontinuous and inverse phases in different ABCP systems.