Alternating Gyroid Network Structure in an ABC Miktoarm Terpolymer Comprised of Polystyrene and Two Polydienes

Supertwisted Chiral Gyroid Mesophase in Chiral Rod-Like Compounds

Among the intriguing bicontinuous self-assembled structures, the gyroid cubic is the most ubiquitous. It is found in block and star polymers, surfactants with or without solvent, in thermotropic liquid crystals with end- or side-chains, and in biosystems providing structural color and modelling cell mitosis. It contains two interpenetrating networks of opposite chirality and is thus achiral if, as usual, the content of the two nets is the same. However, we now find that this is not the case for strongly chiral compounds. While achiral molecules follow the opposite twists of nets 1 and 2, molecules with a chiral center in their rod-like core fail to follow the 70° twist between junctions in net 2 and instead wind against it by -110° to still match the junction orientation. The metastable chiral gyroid is a high-entropy high-heat-capacity mesophase. The homochirality of its nets makes the CD signal of the thienofluorenone compounds close to that in the stable I23 phase with 3 isochiral nets.

Quo Vadis Carbanionic Polymerization?

Living anionic polymerization will soon celebrate 70 years of existence. This living polymerization is considered the mother of all living and controlled/living polymerizations since it paved the way for their discovery. It provides methodologies for synthesizing polymers with absolute control of the essential parameters that affect polymer properties, including molecular weight, molecular weight distribution, composition and microstructure, chain-end/in-chain functionality, and architecture. This precise control of living anionic polymerization generated tremendous fundamental and industrial research activities, developing numerous important commodity and specialty polymers. In this Perspective, we present the high importance of living anionic polymerization of vinyl monomers by providing some examples of its significant achievements, presenting its current status, giving several insights into where it is going (Quo Vadis) and what the future holds for this powerful synthetic method. Furthermore, we attempt to explore its advantages and disadvantages compared to controlled/living radical polymerizations, the main competitors of living carbanionic polymerization.

Synthesis, Characterization and Structure Properties of Biobased Hybrid Copolymers Consisting of Polydiene and Polypeptide Segments

Novel hybrid materials of the PB-b-P(o-Bn-L-Tyr) and PI-b-P(o-Bn-L-Tyr) type (where PB: 1,4/1,2-poly(butadiene), PI: 3,4/1,2/1,4-poly(isoprene) and P(o-Bn-L-Tyr): poly(ortho-benzyl-L-tyrosine)) were synthesized through anionic and ring-opening polymerization under high-vacuum techniques. All final materials were molecularly characterized through infrared spectroscopy (IR) and proton and carbon nuclear magnetic resonance (1H-NMR, 13C-NMR) in order to confirm the successful synthesis and the polydiene microstructure content. The stereochemical behavior of secondary structures (α-helices and β-sheets) of the polypeptide segments combined with the different polydiene microstructures was also studied. The influence of the α-helices and β-sheets, as well as the polydiene chain conformations on the thermal properties (glass transition temperatures, thermal stability, α- and β-relaxation) of the present biobased hybrid copolymers, was investigated through differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dielectric spectroscopy (DS). The obtained morphologies in thin films for all the synthesized materials via atomic force microscopy (AFM) indicated the formation of polypeptide fibrils in the polydiene matrix.

Bicontinuous Gyroid Phase of a Water-Swollen Wedge-Shaped Amphiphile: Studies with In-Situ Grazing-Incidence X-ray Scattering and Atomic Force Microscopy

We report on formation of a bicontinuous double gyroid phase by a wedge-shaped amphiphilic mesogen, pyridinium 4′-[3″,4″,5″-tris-(octyloxy)benzoyloxy]azobenzene-4-sulfonate. It is found that this compound can self-organize in zeolite-like structures adaptive to environmental conditions (e.g., temperature, humidity, solvent vapors). Depending on the type of the phase, the structure contains 1D, 2D, or 3D networks of nanometer-sized ion channels. Of particular interest are bicontinuous phases, such as the double gyroid phase, as they hold promise for applications in separation and energy. Specially designed environmental cells compatible with grazing-incidence X-ray scattering and atomic force microscopy enable simultaneous measurements of structural parameters/morphology during vapor-annealing treatment at different temperatures. Such in-situ approach allows finding the environmental conditions at which the double gyroid phase can be formed and provide insights on the supramolecular structure of thin films at different spatial levels.

Synthesis, characterization and self-assembly of linear and miktoarm star copolymers of exclusively immiscible polydienes

Model linear PB_1,4-b-PI_3,4 and the corresponding miktoarm star copolymers PB_1,4(PI_3,4)_n=2,3 were synthesized by anionic polymerization/selective chlorosilane chemistry, molecularly characterized and the morphological/thermal properties were reported.

New complexes of liquid crystal discotic triphenylenes: induction of the double gyroid phase

Electron donor-acceptor liquid crystals have been attracting considerable attention due to possible applications in optoelectronics and photonics. The creation of such charge transfer complexes is a powerful and flexible instrument for modifying the structures and properties compared to those of the initial components. In the present work, such an approach is exemplified on new complexes formed via non-covalent interactions of triphenylene discotics, namely, 2,3,6,7,10,11-hexakis(pentyloxy) triphenylene (H5T) and 2-(acryloyloxypropyloxy)-3,6,7,10,11-pentapentylox-triphenylene (TPh-3A), with an electron acceptor, β-(2,4,7-trinitro-9-fluorenylideneaminooxy) propionic acid (TNF-carb). The structure of thin supported films of H5T, TPh-3A and their blends with TNF-carb was investigated by grazing-incidence wide-angle X-ray scattering using a synchrotron source. At room temperature, the pristine discotics crystallize in orthorhombic unit cells whereas the self-assembly of H5T and TPh-3A with TNF-carb results in a double gyroid and hexagonal phases, respectively. Formation of the double gyroid phase with the lattice parameter of 36.5 Å is driven by phase separation between the aromatic and alkyl regions of the system. It is supposed that the TNF-carb molecules of the complex are positioned in the nodes of the structure while the H5T molecules are located in the struts adjoining the nodes via triple junctions. For the hexagonal crystal of the TPh-3A/TNF-carb complex, the acceptor molecules are likely located in the interstices between the neighboring supramolecular columns of TPh-3A. The molecular structures of the blends were also explored by means of FTIR spectroscopy. A detailed FTIR spectra analysis illustrates fine changes in inter-molecular bonds. For example, the initially dimerized acceptor molecules totally disappear in the complex structures whereas in TPh-3A/TNF-carb additional H-bonds between the carboxylate group in TNF-carb and the ester group of TPh-3A form. The experimental data allows putting forward possible molecular models of the complex structures.

Dendrons and Dendritic Terpolymers: Synthesis, Characterization and Self-Assembly Comparison

To the best of our knowledge, this is the very first time that a thorough study of the synthetic procedures, molecular and thermal characterization, followed by structure/properties relationship for symmetric and non-symmetric second generation (2-G) dendritic terpolymers is reported. Actually, the synthesis of the non-symmetric materials is reported for the first time in the literature. Anionic polymerization enables the synthesis of well-defined polymers that, despite the architecture complexity, absolute control over the average molecular weight, as well as block composition, is achieved. The dendritic type macromolecular architecture affects the microphase separation, because different morphologies are obtained, which do not exhibit long range order, and various defects or dislocations are evident attributed to the increased number of junction points of the final material despite the satisfactory thermal annealing at temperatures above the highest glass transition temperature of all blocks. For comparison reasons, the initial dendrons (miktoarm star terpolymer precursors) which are connected to each other in order to synthesize the final dendritic terpolymers are characterized in solution and in bulk and their self-assembly is also studied. A major conclusion is that specific structures are adopted which depend on the type of the core connection between the ligand and the active sites of the dendrons.

Self-Assembly of Low-Molecular-Weight Asymmetric Linear Triblock Terpolymers: How Low Can We Go?

The synthesis of two (2) novel triblock terpolymers of the ABC type and one (1) of the BAC type, where A, B and C are chemically different segments, such as polystyrene (PS), poly(butadiene) (PB1,4) and poly(dimethylsiloxane) (PDMS), is reported; moreover, their corresponding molecular and bulk characterizations were performed. Very low dimensions are evident from the characterization in bulk from transmission electron microscopy studies, verified by small-angle X-ray data, since sub-16 nm domains are evident in all three cases. The self-assembly results justify the assumptions that the high Flory-Huggins parameter, χ, even in low molecular weights, leads to significantly well-ordered structures, despite the complexity of the systems studied. Furthermore, it is the first time that a structure/properties relationship was studied for such systems in bulk, potentially leading to prominent applications in nanotechnology and nanopatterning, for as low as sub-10 nm thin-film manipulations.