Self-Assembly of Stereoblock Copolymers Driven by the Chain Folding of Discrete Poly(d-lactic acid-b-l-lactic acid) via Intramolecular Stereocomplexation

Chiral Communication between Enantiomeric Sergeants and Achiral Soldiers in Racemic Triblock Copolymers with Heterochiral Cores for Triggering Multiple Helicity Inversions

Amplification of asymmetry in complex supramolecular/polymer system results from the delicate interplay of chiral and achiral structures. Here, a novel approach to the racemic sergeants and soldiers (S&S) effect, using enantiomeric sergeants (Sgt.) and achiral soldiers (Sold.), achieves unique precise control over both intensity and sign of global chirality. Chiroptical assemblies of different dimensions in racemic S&S copolymers can be constructed in situ via polymerization-induced chiral self-assembly (PICSA). We systemically investigated chiral communication pathways between chiral-chiral, chiral-achiral, and two oppositely configured azobenzene (Azo) segments, which robustly affect the global chiroptical activity of the racemic S&S assemblies. Chain length-, Sgt./Sold. ratios-, and temperature-dependent CD/UV/Vis, small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results provided insights into the kinetics for chiroptical inversions. LC phase transitions, the helical preferences of the Sgt. and Sold. units, and the stability of the "chiral core" allow racemic S&S copolymer assemblies to exhibit chiral conflict between heterochiral blocks in an enantioselective fashion.

Self-Assembly of Amorphous 2D Polymer Nanodiscs with Tuneable Size, pH-Responsive Degradation and Controlled Drug Release

Amphiphilic bottlebrush block copolymers (BBCs) with tadpole-like, coil-rod architecture can be used to self-assemble into functional polymer nanodiscs directly in water. The hydrophobic segments of the BBC were tuned via the ratio of ethoxy-ethyl glycidyl ether (EE) to tetrahydropyranyl glycidyl ether (TP) within the grafted polymer sidechains. In turn, this variation controlled the sizes, pH-responsiveness, and drug loading capacity of the self-assembled nanodiscs. Notably, as EE exhibited faster hydrolysis than TP, the nanodiscs featured variable degradation rates under mild acidic conditions, aiding small molecule release and time-dependent and complete degradation of discs into fully water-soluble copolymers. The nanodiscs demonstrated biocompatibility and cellular uptake by breast cancer cells, underscoring their potential development into drug delivery systems.

Dynamically Switchable Global Chirality in Racemic Polymer Systems

Any polymers composed of racemic segments are obviously optically inactive and lack any chiroptical applications. Here, we present an intriguing method for precisely generating global chirality in racemic copolymer assemblies without any external asymmetrical intervention via step-wise polymerization-induced chiral self-assembly (PICSA). Global supramolecular chirality of the nanoaggregates could be dynamically switched by the two diametrically opposed chiral conflict effects: "first come, first serve" effect and "late-comer lives above" effect, which can be controlled by the precisely specified the number and sequence of enantiomeric segments. Significantly, the supramolecular stacking manners of the racemic mesogenic building units as well as the liquid crystallinity of the solvophobic core play a crucial role for the chiral communication pathway of enantiomeric mesogens. Furthermore, such switchable global chirality in racemic polymers is broadly applicable and well regulable. We propose that this research may challenge the notion that racemic systems lack optical activity while highlighting their potential applications in functional racemic polymer materials and providing insights into the evolution of racemates towards homochirality on early Earth.

Chain Shuttling Enantioselective Polymerization: An Effective Strategy for Synthesizing Stereoblock Polythioethers

Herein, we propose to synthesize stereoblock polythioethers through the chain shuttling enantioselective ring-opening polymerization (ROP) of thiiranes. The use of diastereoisomeric dinuclear Cr complexes with optimized steric hindrance allowed the production of polythioethers with both a head-to-tail content and isotacticity of >99%. In particular, the introduction of dithiols enabled the synthesis of stereoblock polythioethers via a chain shuttling process, thus producing sulfhydryl-telechelic polythioethers with tunable thermal properties. Experimental results and density functional theory calculations indicate that the configuration of the chiral axle of the dinuclear Cr complex determines the enantioselectivity of the asymmetric ROP of thiiranes.

Nanoscale polymer discs, toroids and platelets: a survey of their syntheses and potential applications

Polymer self-assembly has become a reliable and versatile workhorse to produce polymeric nanomaterials. With appropriate polymer design and monomer selection, polymers can assemble into shapes and morphologies beyond well-studied spherical and cylindrical micellar structures. Steadfast access to anisotropic polymer nanoparticles has meant that the fabrication and application of 2D soft matter has received increasing attention in recent years. In this review, we focus on nanoscale polymer discs, toroids, and platelets: three morphologies that are often interrelated and made from similar starting materials or common intermediates. For each morphology, we illustrate design rules, and group and discuss commonly used self-assembly strategies. We further highlight polymer compositions, fundamental principles and self-assembly conditions that enable precision in bottom-up fabrication strategies. Finally, we summarise potential applications of such nanomaterials, especially in the context of biomedical research and template chemistry and elaborate on future endeavours in this space.

Precision Sequence-Defined Polymers: From Sequencing to Biological Functions

Precise sequence-defined polymers (SDPs) with uniform chain-to-chain structure including chain length, unit sequence, and end functionalities represent the pinnacle of sophistication in the realm of polymer science. For example, the absolute control over the unit sequence of SDPs allows for the bottom-up design of polymers with hierarchical microstructures and functions. Accompanied with the development of synthetic techniques towards precision SDPs, the decoding of SDP sequences and construction of advanced functions irreplaceable by other synthetic materials is of central importance. In this Minireview, we focus on recent advances in SDP sequencing techniques including tandem mass spectrometry (MS), chemically assisted primary MS, as well as other non-destructive sequencing methods such as nuclear magnetic resonance (NMR) spectroscopy, circular dichroism (CD), and nanopore sequencing. Additionally, we delve into the promising prospects of SDP functions in the area of cutting-edge biological research. Topics of exploration include gene delivery systems, the development of hybrid materials combining SDPs and nucleic acids, protein recognition and regulation, as well as the interplay between chirality and biological functions. A brief outlook towards the future directions of SDPs is also presented.

Unraveling Dynamic Helicity Inversion and Chirality Transfer through the Synthesis of Discrete Azobenzene Oligomers by an Iterative Exponential Growth Strategy

Unraveling the chirality transfer mechanism of polymer assemblies and controlling their handedness is beneficial for exploring the origin of hierarchical chirality and developing smart materials with desired chiroptical activities. However, polydisperse polymers often lead to an ambiguous or statistical evaluation of the structure-property relationship, and it remains unclear how the iterative number of repeating units function in the helicity inversion of polymer assemblies. Herein, we report the macroscopic helicity and dynamic manipulation of the chiroptical activity of supramolecular assemblies from discrete azobenzene-containing oligomers (azooligomers), together with the helicity inversion and morphological transition achieved solely by changing the iterative chain lengths. The corresponding assemblies also differ from their polydisperse counterparts in terms of thermodynamic properties, chiroptical activities, and morphological control.

Cascade Energy Transfer and White-Light Emission in Chirality-Controlled Crystallization-Driven Two-Dimensional Co-assemblies from Donor and Acceptor Dye-Conjugated Polylactides

Achieving predictable and programmable two-dimensional (2D) structures with specific functions from exclusively organic soft materials remains a scientific challenge. This article unravels stereocomplex crystallization-driven self-assembly as a facile method for producing thermally robust discrete 2D-platelets of diamond shape from biodegradable semicrystalline polylactide (PLA) scaffolds. The method involves co-assembling two PLA stereoisomers, namely, PY-PDLA and NMI-PLLA, which form stereocomplex (SC)-crystals in isopropanol. By conjugating a well-known Förster resonance energy transfer (FRET) donor and acceptor dye, namely, pyrene (PY) and naphthalene monoimide (NMI), respectively, to the chain termini of these two interacting stereoisomers, a thermally robust FRET process can be stimulated from the 2D array of the co-assembled dyes on the thermally resilient SC-PLA crystal surfaces. Uniquely, by decorating the surface of the SC-PLA crystals with an externally immobilized guest dye, Rhodamine-B, similar diamond-shaped structures could be produced that exhibit pure white-light emission through a surface-induced two-step cascade energy transfer process. The FRET response in these systems displays remarkable dependence on the intrinsic crystalline packing, which could be modulated by the chirality of the co-assembling PLA chains. This is supported by comparing the properties of similar 2D platelets generated from two homochiral PLLAs (PY-PLLA and NMI-PLLA) labeled with the same FRET pair.