Chemistry Reference
In-Depth Information
5.1.1. Supramolecular Polymers
Supramolecular polymers can be defined as “the formation of polymeric materials via
noncovalent interactions using self-assembly” and can be categorized into main and
side chain supramolecular polymers (Bosman et al. 2003). The vast majority of
reports in the literature focus on main chain supramolecular polymers, materials
that are held together by noncovalent interactions such as hydrogen bonding, metal
coordination, or coulombic interactions (Brunsveld et al. 2001). Because the
degree of polymerization and ultimately the stability of the polymer backbone
are dependent upon the strength of the noncovalent interaction, main chain
supramolecular polymers often utilize recognition motifs that have very strong
binding efficiencies.
In contrast, side chain supramolecular polymers are polymers in which the
polymer backbone is based on covalent bonds but the side chains of the polymers
are noncovalently functionalized (Pollino and Weck 2005; Weck 2007). The
unique advantage of noncovalent side chain functionalization is that it combines
the robustness of the covalent main chain polymer with the reversibility
and flexibility of noncovalent interactions; hence, it has been used in synthesizing
“tailor-made” materials with controlled architectures and properties. Furthermore,
because the degree of polymerization and the stability of the polymer backbone
are independent of the strength of the noncovalent interaction, a vast variety
of interactions ranging from weak to the strongest noncovalent interactions
can be utilized in these systems. Hydrogen bonding, metal coordination,
coulombic interactions, and dipole-dipole interactions are some of the most
extensively employed noncovalent interactions used for side chain functionalization
of polymers.
By choosing the appropriate noncovalent interaction, quantitative functiona-
lization of polymer scaffolds can be obtained. Such a strategy offers an important
advantage in the field of material design, because by simply varying the desired non-
covalent functionality self-assembled along a polymeric scaffold, a single parent
polymer scaffold can be transformed into a family of functionalized polymers with
very different and tunable physical and chemical properties. Therefore, this strategy
is capable of circumventing lengthy sequential synthetic steps based on covalent
chemistry and thus has the potential to allow for easier, faster, and more efficient
materials optimization.
Depending on the desired application, appropriate polymeric scaffolds can be
synthesized depending upon the synthetic feasibility of the covalent scaffolds. For
example, copolymers such as random, alternating, diblock, and triblock copolymers,
as well as cross-linked polymeric networks, hyperbranched polymers, dendrimers,
and graft polymers have been employed as polymeric scaffolds for side chain
functionalization. Furthermore, functional polymer backbones such as liquid
crystalline polymers (Kato et al. 1996) and biodegradable polymers (Dankers et al.
2006), in addition to polymeric macrostructures such as vesicles, aggregates,
networks, and inorganic materials (such as nanoparticles) have been utilized
(Carroll et al. 2002).
