Crown Ether-Based Supramolecular Polymers: From Synthesis to Self-Assembly

Supramolecular polymers not only possess many advantages of traditional polymers, but also have many unique characteristics. Supramolecular polymers can be constructed by self-assembly of various noncovalent interactions. Host-guest interaction, as one important type of noncovalent interactions, has been widely applied to construct supramolecular polymers. From the perspective of classification of the recognition system motifs, host-guest recognition motifs mainly include crown ether, cyclodextrin, calixarene, cucurbituril, and pillararene-based host-guest recognition pairs. Crown ethers, as the first-generation macrocyclic hosts, have played a very important part in the development of supramolecular chemistry. Due to the easy modification of crown ethers, various crown ether derivatives have been prepared by attaching some functional groups to the edges of crown ethers, which endowed them with some interesting properties and made them ideal candidates for the fabrication of supramolecular polymers. This review gives a review of the preparation of crown ether-based supramolecular polymers (CSPs) and summarizes crown ether-based recognition pairs, organization methods, topological structures, stimuli-responsiveness, and functional characteristics.

A dual redox-responsive supramolecular amphiphile fabricated by selenium-containing pillar[6]arene-based molecular recognition

A dual redox-responsive pillar[6]arene-based supramolecular amphiphile was fabricated in water. The self-assembly behavior of this supramolecular amphiphile in response to dual redox stimuli was investigated.

Supramolecular Graft Copolymerization of a Polyester by Guest-Selective Encapsulation of a Self-Assembled Capsule

Repeating guest units of polyesters poly-(R)-2 were selectively encapsulated by capsule 1(BF₄ )₄ to produce supramolecular graft polymers. The encapsulation of the guest units was confirmed by ¹ H NMR spectroscopy. The graft polymer structures were confirmed by the increase in the hydrodynamic radii and the solution viscosities of the polyesters upon complexation of the capsule. After the capsule was formed, atomic force microscopy showed extension of the polyester chains. The introduction of the graft chains onto poly-(R)-2 resulted in the main chain of the polymer having an M-helical morphology. The complexation of copolymers poly-[(R)-2-co-(S)-2] by the capsule gave rise to the unique chiral amplification known as the majority-rules effect.

Fabrication of Dual-Redox Responsive Supramolecular Copolymers Using a Reducible β-Cyclodextran-Ferrocene Double-Head Unit

Self-assembly of amphiphilic block copolymers into well-defined nanostructures as drug delivery systems for the treatment of cancer has been a hot subject of research. However, sequential polymerizations synthesized amphiphilic block copolymers with covalent links suffered mainly from multistep synthesis and purification procedures as well as repeated optimization of polymer composition to form aggregates with well-defined structures. To overcome these drawbacks, supramolecular amphiphilic block copolymers with noncovalent links were developed to provide simplicity as required. Herein, we designed and prepared a reducible β-cyclodextran (β-CD)-ferrocene (Fc) double-head unit from which a dual-redox responsive supramolecular amphiphilic copolymer was fabricated together with a traditional polymer block through supramolecular induced polymerization. Typically, well-defined supramolecular micelles and vesicles were fabricated, respectively. Due to the integration of oxidation-sensitive noncovalent β-CD/Fc connections and reduction-sensitive covalent disulfide bridges in the polymer backbone, the resulting supramolecular micelles and vesicles showed structural deformation and accelerated drug release in response to both intracellular reducing and oxidizing environments, thus, presenting a new platform for both reactive oxygen species (ROS) and glutathione (GSH)-triggered anticancer drug delivery.

Amphiphilic Graft Copolymer Nanospheres: From Colloidal Self-Assembly to CO2 Capture Membranes

Colloidal nanosphere self-assembly effectively generates ordered nanostructures, prompting tremendous interest in many applications such as photonic crystals and templates for inverse opal fabrication. Here we report the self-assembly of low-cost, graft copolymer nanospheres for CO2 capture membranes. Specifically, poly(dimethylsiloxane)-graft-poly(4-vinylpyridine) (PDMS-g-P4VP) is synthesized via one-pot, free radical dispersion polymerization to give discrete monodisperse nanospheres. These nanospheres comprise a surface-anchored highly permeable PDMS layer and internal CO2-philic P4VP spherical core. Their diameter is controllable below the submicrometer range by varying grafting ratios. The colloidal dispersion forms a long-range, close-packed hexagonal array on a substrate by inclined deposition and convective assembly. The array shows dispersion medium-dependent packing characteristics. A thermodynamic correlation is determined using different solvents to obtain stable PDMS-g-P4VP dispersions and interpreted in terms of Flory-Huggins interaction parameter. As a proof-of-concept, the implementation of these nanospheres into membranes simultaneously enhances the CO2 permeability and CO2/N2 selectivity of PDMS-based transport matrixes. Upon physical aging of the solution, the CO2/N2 selectivity is improved up to 26, one of the highest values for highly permeable PDMS-based polymeric membranes.

Facile construction of fluorescent polymeric aggregates with various morphologies by self-assembly of supramolecular amphiphilic graft copolymers

Facile construction of fluorescent polymeric aggregates with various morphologies was realized by self-assembly of supramolecular amphiphilic graft copolymers.

Supramolecular nanoparticles constructed by balancing the forces between attractive host–guest and repulsive electrostatic interactions in two positively charged polymers

A novel type of supramolecular nanoparticle (SNP) was self-assembled based on the balance of forces including attractive supramolecular host–guest interactions and repulsive electrostatic interactions between the host and the guest polymers.