Supramolecular Star-Shaped Poly(ethylene glycol) Based on a [2 × 2] Grid-Like Metal Complex

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.

[2 × 2] metallo-supramolecular grids based on 4,6-bis((1H-1,2,3-triazol-4-yl)-pyridin-2-yl)-2-phenylpyrimidine ligands: from discrete [2 × 2] grid structures to star-shaped supramolecular polymeric architectures

The self-assembly of bis-tridentate ligands leads to the spontaneous formation of [2 × 2] grid-like metal complexes. However, the synthesis of such ligands is rather cumbersome. In the work, we demonstrate a straightforward synthesis route to prepare bis-tridentate 4,6-bis((1H-1,2,3-triazol-4-yl)-pyridin-2-yl)-2-phenylpyrimidine ligands through double CuAAC click chemistry with 4,6-bis(6-ethynylpyridin-2-yl)-2-phenylpyrimidine as well as their self-assembly into [2 × 2] grid-like metal complexes. In addition, four macromolecular ligands were synthesized starting from azido-end-functionalized poly(2-ethyl-2-oxazoline) (PEtOx) or poly(ethylene glycol) (PEG). These macromolecular ligands were used in the construction of star-shaped supramolecular polymers through complexation with transition metal ions (e.g., Fe2+ or Zn2+). The successful fabrication of complexes and star-shaped polymers was confirmed by UV-vis titration measurements and MALDI-TOF mass spectrometry. However, the chemical structure of the polymer was found to have a strong influence on the [2 × 2] grid formation, which was successful with the PEG-ligands but not with the PEtOx-ligands, while the molecular weight of the PEG did not interfere with grid formation.

Synthetic methodologies and spatial organization of metal chelate dendrimers and star and hyperbranched polymers

The synthetic methodologies, physico-chemical peculiarities, properties, and structure of metal chelate dendrimers and star and hyperbranched polymers are considered.

A supramolecular miktoarm star polymer based on porphyrin metal complexation in water

A novel strategy is reported for preparing a supramolecular miktostar polymer based on complexation of a metalloporphyrin based four-arm star polymer and a pyridine functionalized polymer.

Metallo/clusto hybridized supramolecular polymers

The introduction of metal centers to a supramolecular polymer system is an important approach to fabricate hybrid supramolecular polymers with synergistic properties between their inorganic and organic components, which is mainly realized through two strategies: one is the embedment of metal ions through metal-ligand coordination to form metallo-supramolecular polymers (MSPs); the other is using metal-containing clusters as hybrid building blocks to prepare clusto-supramolecular polymers (CSPs). The available paradigms of MSPs and CSPs not only exhibit the unique functions of metal centers but also hold the good processing ability and the stimuli-responsibility of dynamically bonded polymeric structures, thus representing a new class of hybrid soft materials. In this review, the development and recent progress of MSPs and CSPs are discussed in detail, including their structure design, synthetic procedures and related properties. Finally, challenges and potential areas in metal-containing supramolecular polymers are outlooked.