ligand(s) and the corresponding metal ion, thermodynamical stable polymers are
formed. The physics and properties of these polymers are comparable to classical
covalent polymers (Staudinger-like polymers). For a low binding constant, polymeric assemblies only form in the solid state, not in solution (classical inorganic
coordination polymers). In contrast, medium binding constants also enable the
formation of macromolecular assemblies in solution. The binding constant
K depends on several external parameters like pH value, temperature, and solvent
polarity as well as on the ligand design and the corresponding metal ion. K can be
increased by multiple interacting binding sites, like chelating ligands or multivalent
metal ions. Accordingly, for every metal–ligand pair, a detailed investigation of the
thermodynamic and kinetic properties is required when a suitable metal–ligand
combination is chosen [43].
Kinetically labile metal–ligand interactions open a field for materials with
remarkable properties by assembling, disassembling, and reconstructing in a
dynamic way. These weak interactions are particularly utilized in materials that
have the ability to self-repair [44], self-anneal, and self-correct under certain
conditions [45]. Most metallopolymers contain ionic metal complexes. The combination of these positively charged moieties and the corresponding counterions can
lead to interesting properties. The melt morphology of diblock copolymers with
central metal complexes as linking unit strongly depends on the type and size of the
counterions. The groups of Schubert and Gohy investigated the self-assembly of
systems having ruthenium ions as the metal, complexed with terpyridine ligands
attached to polystyrene (PS) and poly(ethylene oxide) (PEO) [46]. In bulk, the
electrostatic interactions between the metal–ligand complex ions and their counterions drive them to form aggregates [47]. This leads to morphologies that are
different to their covalent counterpart. Al-Hussein et al. reported highly ordered
lamellar structures in the melt of a PS 20 -[Ru]-PEO 70 diblock copolymer when bulky
counterions were used. Thereby, the metal–ligand complex acting as ionomer is
responsible for triggering the microphase separation. This observation can be used
to tune the morphology of the metallo(supramolecular) copolymers [48]. The
electrostatic interaction between the metal–ligand ions and their associated counterions drives them to form aggregates.
2 Ionomers
The described morphological features for metallopolymers show some parallels
with the situation in common ionomers, in which the presence of ionic clusters
contributes strongly to the healing process. This has also to be considered for selfhealing metallopolymers featuring (ionic) clusters, comparably to ionomers. These
latter materials were defined by Tant and Wilkes as a class of ion-containing
copolymers. Thereby, the maximum ion group content is about 15 mol% [49]. To
distinguish these systems from polyelectrolytes, Eisenberg and Rinaudo further
developed the definition, so that ionomer bulk properties are organized by ionic
242
B. Sandmann et al.
formed. The physics and properties of these polymers are comparable to classical
covalent polymers (Staudinger-like polymers). For a low binding constant, polymeric assemblies only form in the solid state, not in solution (classical inorganic
coordination polymers). In contrast, medium binding constants also enable the
formation of macromolecular assemblies in solution. The binding constant
K depends on several external parameters like pH value, temperature, and solvent
polarity as well as on the ligand design and the corresponding metal ion. K can be
increased by multiple interacting binding sites, like chelating ligands or multivalent
metal ions. Accordingly, for every metal–ligand pair, a detailed investigation of the
thermodynamic and kinetic properties is required when a suitable metal–ligand
combination is chosen [43].
Kinetically labile metal–ligand interactions open a field for materials with
remarkable properties by assembling, disassembling, and reconstructing in a
dynamic way. These weak interactions are particularly utilized in materials that
have the ability to self-repair [44], self-anneal, and self-correct under certain
conditions [45]. Most metallopolymers contain ionic metal complexes. The combination of these positively charged moieties and the corresponding counterions can
lead to interesting properties. The melt morphology of diblock copolymers with
central metal complexes as linking unit strongly depends on the type and size of the
counterions. The groups of Schubert and Gohy investigated the self-assembly of
systems having ruthenium ions as the metal, complexed with terpyridine ligands
attached to polystyrene (PS) and poly(ethylene oxide) (PEO) [46]. In bulk, the
electrostatic interactions between the metal–ligand complex ions and their counterions drive them to form aggregates [47]. This leads to morphologies that are
different to their covalent counterpart. Al-Hussein et al. reported highly ordered
lamellar structures in the melt of a PS 20 -[Ru]-PEO 70 diblock copolymer when bulky
counterions were used. Thereby, the metal–ligand complex acting as ionomer is
responsible for triggering the microphase separation. This observation can be used
to tune the morphology of the metallo(supramolecular) copolymers [48]. The
electrostatic interaction between the metal–ligand ions and their associated counterions drives them to form aggregates.
2 Ionomers
The described morphological features for metallopolymers show some parallels
with the situation in common ionomers, in which the presence of ionic clusters
contributes strongly to the healing process. This has also to be considered for selfhealing metallopolymers featuring (ionic) clusters, comparably to ionomers. These
latter materials were defined by Tant and Wilkes as a class of ion-containing
copolymers. Thereby, the maximum ion group content is about 15 mol% [49]. To
distinguish these systems from polyelectrolytes, Eisenberg and Rinaudo further
developed the definition, so that ionomer bulk properties are organized by ionic
242
B. Sandmann et al.