Supramolecular Synthesis of Star Polymers.

Invited for this month's cover are the collaborating groups of Prof. Dr Takeharu Haino at Hiroshima University (Japan) and Dr Natsumi Nitta at the University of Chicago (USA). The cover picture shows cartoons of miktoarm A8Bn star and graft copolymers formed by molecular recognition of a self-assembled capsule possessing eight polymer chains and guest-terminated and guest-centered polymers. Read the full text of the review at 10.1002/cplu.20240014.

Supramolecular Synthesis of Star Polymers.

Supramolecular polymers, in which monomers are assembled via intermolecular interactions, have been extensively studied. The fusion of supramolecular polymers with conventional polymers has attracted the attention of many researchers. In this review article, the recent progress in the construction of supramolecular star polymers, including regular star polymers and miktoarm star polymers, is discussed. The initial sections briefly provide an overview of the conventional classification and synthesis methods for star polymers. Coordination-driven self-assembly was investigated for the supramolecular synthesis of star polymers. Star polymers with multiple polymer chains radiating from metal-organic polyhedra (MOPs) have also been described. Particular focus has been placed on the synthesis of star polymers featuring supramolecular cores formed through hydrogen-bonding-directed self-assembly. After describing the synthesis of star polymers based on host-guest complexes, the construction of miktoarm star polymers based on the molecular recognition of coordination capsules is detailed.

Vinylogous Urea-Urethane Vitrimers: Accelerating and Inhibiting Network Dynamics through Hydrogen Bonding.

Vinylogous urethane (VUO ) based polymer networks are widely used as catalyst-free vitrimers that show rapid covalent bond exchange at elevated temperatures. In solution, vinylogous ureas (VUN ) undergo much faster bond exchange than VUO and are highly dynamic at room temperature. However, this difference in reactivity is not observed in their respective dynamic polymer networks, as VUO and VUN vitrimers prepared herein with very similar macromolecular architectures show comparable stress relaxation and creep behavior. However, by using mixtures of VUO and VUN linkages within the same network, the dynamic reactions can be accelerated by an order of magnitude. The results can be rationalized by the effect of intermolecular hydrogen bonding, which is absent in VUO vitrimers, but is very pronounced for vinylogous urea moieties. At low concentrations of VUN , these hydrogen bonds act as catalysts for covalent bond exchange, while at high concentration, they provide a pervasive vinylogous urea - urethane (VU) network of strong non-covalent interactions, giving rise to phase separation and inhibiting polymer chain dynamics. This offers a straightforward design principle for dynamic polymer materials, showing at the same time the possible additive and synergistic effects of supramolecular and dynamic covalent polymer networks.

Synthesis of Supramolecular A8 Bn Miktoarm Star Copolymers by Host-Guest Complexation.

We report a new synthetic method to construct supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers by host-guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size-exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in the bulk. The micro-Brownian motion of the A8 B4 structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.

Self-Healing Supramolecular Materials Constructed by Copolymerization via Molecular Recognition of Cavitand-Based Coordination Capsules.

The repeating guest units of poly-(R)-2 were selectively encapsulated by the self-assembled capsule poly-1 possessing eight polymer side chains to form the supramolecular graft polymer (poly-1)n ⋅poly-(R)-2. The encapsulation of the guest units was confirmed by 1 H NMR spectroscopy and the DOSY technique. The hydrodynamic radius of the graft polymer structure was greatly increased upon the complexation of poly-1. The supramolecular graft polymer (poly-1)n ⋅poly-(R)-2 was stably formed in the 1:1 host-guest ratio, which increased the glass transition temperature by more than 10 °C compared to that of poly-1. AFM visualized that (poly-1)n ⋅poly-(R)-2 formed the networked structure on mica. The (poly-1)n ⋅poly-(R)-2 gelled in 1,1,2,2-tetrachloroethane, which led to fabrication of distinct viscoelastic materials that demonstrated self-healing behavior in a tensile test.

Facile Synthesis of an Eight-Armed Star-Shaped Polymer via Coordination-Driven Self-Assembly of a Four-Armed Cavitand.

The polystyrene chains were installed at the lower rim of a resorcinarene-based cavitand via reversible addition-fragmentation (RAFT) polymerization to form a four-armed star-shaped polymer. A star-shaped polystyrene-functionalized supramolecular capsule was prepared through the coordination-driven self-assembly of the four-armed start-shaped polymer with silver ions. The eight-armed start-shaped supramolecular capsule encapsulated 4,4'-diacetoxybiphenyl as did a cavitand-based self-assembled capsule. A DOSY measurement indicated that the eight-armed star-shaped polymer was twice as large as the four-armed star-shaped polymer. The solution behaviors of these compounds resulted in a difference in their zero-shear viscosities.