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diaminopyridine derivatives or biologically important groups such as biotin, adenine,
and so forth using ring-opening methathesis polymerization (ROMP). Sleiman's
group then investigated their self-assembly into nanostructures (such as star micelles)
using hydrogen bonding moieties to control the formation of the three-dimensional
structures (Bazzi et al. 2003; Chen et al. 2005).
Carroll and colleagues (2003) carried out postpolymerization functionalization of
polystyrene copolymers containing randomly dispersed chloromethylstyrene func-
tional groups with 2,4-diaminotriazine or 2,6-diaminopyridine derivatives, yielding
polystyrene copolymers with terminal hydrogen bonding recognition moieties
along the side chains. These scaffolds were then functionalized noncovalently
using hydrogen bonding with a variety of small molecules, including sesquiloxane,
to form inorganic-organic hybrid materials (Carroll et al. 2003). Such a strategy
of obtaining a host of different materials from the same parent polymeric scaffold
just by varying the anchoring moieties was named “plug and play” polymers by
the Rotello group (Carroll et al. 2003).
5.2.2. Side Chain Functionalization Using Metal Coordination
The second major class of noncovalent interactions that has been employed exten-
sively for polymeric functionalization is metal coordination. Side chain metal func-
tionalized polymers possess the characteristic properties of both the metal and the
polymer components, giving rise to a variety of hybrid materials thereby exhibiting
metal-specific properties such as conductivity and magnetism while maintaining
the benefit of solubility and processability because of the polymer backbone.
These metal-ligand interactions are fairly temperature insensitive compared to
hydrogen bonding interactions. However, they are highly sensitive to ligand displace-
ment reactions and are therefore considered to be chemoresponsive. Advantages of
metal complexes include their highly controlled synthesis; the formation of strong
noncovalent bonds in noncompeting solvents; and the potential application of
metal containing polymers in areas such as supported catalysis (Yu et al. 2005),
electro-optical materials (Long 1995), and chemically responsive gels (Hofmeier
and Schubert 2003).
Side chain metal functionalized polymers fall into two classes according to the
position of the metal complex with respect to the polymer backbone. In the first
class, the metal is covalently tethered to the polymer backbone, whereas the comp-
lementary component, the ligand, is coordinated to the “polymeric scaffold.” In
the second class of side chain metal functionalized polymers, the ligand is covalently
attached to the polymer backbone to form a “polymeric ligand species,” often called a
macroligand, whereas the metal center is then subsequently complexed onto the
polymer. In both cases, the resultant polymers may possess identical structures and
the choice of the synthetic strategy is dependent on the ease of the synthetic
method: the synthesis of polymeric ligand scaffolds is more synthetically accessible
compared to the polymerization of a metal containing monomer because of the
limited number of polymerization methods as a result of the metal intolerance of
most polymerization techniques. Although many examples of side chain metal
