3 Dynamers: Constitutional Dynamic Polymers
3.1 Supramolecular Non-covalent Dynamers
As pointed out above, numerous studies have been devoted to the chemistry of
supramolecular polymers, based on various types of more or less directive
non-covalent interactions of various strengths. These interactions can range from
the organic type [8–21, 44–52], such as hydrogen bonding, to the inorganic type
involving metal ion binding in metallosupramolecular coordination polymers
[22–28, 53–55].
The progressive generation of entities of increasing complexity by hierarchical
build-up at the supramolecular level is a process of major significance for the emergence of complex matter and is subject to active investigation. As an illustration, one
may consider the very first case of a main-chain supramolecular polymer [4–6]. Their
formation and behavior may be dissected into a three-stage conditional process,
starting from complementary molecular components that form supramolecular main
chains through hydrogen bonding. These chains, in turn, assemble into cylindrical
triple-helical columns that finally yield helical fibrils by side-chain entanglement
(Fig. 2). This type of one-dimensional (1D) supramolecular polymer has been visualized by scanning tunneling microscopy (STM), thus confirming the supramolecular
chain-type structure proposed earlier [56].
A two-dimensional (2D) supramolecular polymer array can be generated for
instance from ditopic monomers containing two terminal guanine residues, which
form potassium cation-stabilized supramolecular macrocyclic guanine quartets
(Fig. 3) [57, 58]. A hydrogel is obtained that is reversibly switchable between gel
and sol states through binding and release of the metal cations by a pH-modulated
cryptand ligand. On the other hand, covalent polymers incorporating tris-urea
motifs, derived from carbohydrazide and isocyanate components, establish a 2D
pattern in which one direction (that of the covalent chain) is molecular and the
orthogonal direction (that of the hydrogen bonding between the urea subunits) is
supramolecular [59].
A different approach to the generation of supramolecular polymers resides in first
generating supramolecular monomers and subsequently connecting them through
covalent bonds. Such a process has been realized in oxidative polymerization by
formation of C–C links between ditopic supramolecular building blocks, which
yields supramolecular microcapsules on deposition on a surface (the three steps
are shown in Fig. 4) [60].
3.2 Molecular Covalent Dynamers
Dynamic covalent polymers have been generated by using various reversible
chemical reactions for linking monomers ([61–75] for an early implementation of
Dynamers: From Supramolecular Polymers to Adaptive Dynamic Polymers
159
3.1 Supramolecular Non-covalent Dynamers
As pointed out above, numerous studies have been devoted to the chemistry of
supramolecular polymers, based on various types of more or less directive
non-covalent interactions of various strengths. These interactions can range from
the organic type [8–21, 44–52], such as hydrogen bonding, to the inorganic type
involving metal ion binding in metallosupramolecular coordination polymers
[22–28, 53–55].
The progressive generation of entities of increasing complexity by hierarchical
build-up at the supramolecular level is a process of major significance for the emergence of complex matter and is subject to active investigation. As an illustration, one
may consider the very first case of a main-chain supramolecular polymer [4–6]. Their
formation and behavior may be dissected into a three-stage conditional process,
starting from complementary molecular components that form supramolecular main
chains through hydrogen bonding. These chains, in turn, assemble into cylindrical
triple-helical columns that finally yield helical fibrils by side-chain entanglement
(Fig. 2). This type of one-dimensional (1D) supramolecular polymer has been visualized by scanning tunneling microscopy (STM), thus confirming the supramolecular
chain-type structure proposed earlier [56].
A two-dimensional (2D) supramolecular polymer array can be generated for
instance from ditopic monomers containing two terminal guanine residues, which
form potassium cation-stabilized supramolecular macrocyclic guanine quartets
(Fig. 3) [57, 58]. A hydrogel is obtained that is reversibly switchable between gel
and sol states through binding and release of the metal cations by a pH-modulated
cryptand ligand. On the other hand, covalent polymers incorporating tris-urea
motifs, derived from carbohydrazide and isocyanate components, establish a 2D
pattern in which one direction (that of the covalent chain) is molecular and the
orthogonal direction (that of the hydrogen bonding between the urea subunits) is
supramolecular [59].
A different approach to the generation of supramolecular polymers resides in first
generating supramolecular monomers and subsequently connecting them through
covalent bonds. Such a process has been realized in oxidative polymerization by
formation of C–C links between ditopic supramolecular building blocks, which
yields supramolecular microcapsules on deposition on a surface (the three steps
are shown in Fig. 4) [60].
3.2 Molecular Covalent Dynamers
Dynamic covalent polymers have been generated by using various reversible
chemical reactions for linking monomers ([61–75] for an early implementation of
Dynamers: From Supramolecular Polymers to Adaptive Dynamic Polymers
159