Chemistry Reference
In-Depth Information
5.4. APPLICATIONS OF NONCOVALENTLY FUNCTIONALIZED
SIDE CHAIN COPOLYMERS
Having discussed self-assembly strategies toward noncovalently functionalized
side chain supramolecular polymers as well as studies toward the orthogonality of
using multiple noncovalent interactions in the same system, this section presents
some of the potential applications of these systems as reported in the literature.
The applications based on these systems can be broadly classified into two
areas: 1) self-assembled functional materials and 2)
functionalized reversible
network formation.
5.4.1. Self-Assembled Functional Materials
The majority of applications of side chain functionalized supramolecular polymers
reported in the literature can be classified as self-assembled functional materials.
This strategy involves the noncovalent anchoring of functional moieties such as
mesogens, fluorescent tags, bioactive molecules, metal centers, and so forth to a
polymeric scaffold, resulting in the introduction of function along the polymer and
the formation of self-assembled functionalized materials. Highly recognition group
specific and well-defined assembly is key to this strategy, because nonspecific
side chain functionalization would result in the formation of ill-defined materials.
We will discuss two widely encountered self-assembled functional materials:
supramolecular side chain liquid crystalline polymers (SSCLCPs) and self-assembled
macrostructures.
SSCLCPs.
Over a decade ago, Kumar and coworkers (1992) reported the first
application of hydrogen bonded side chain functionalized polymers. Hydrogen
bonding interactions were used to noncovalently attach mesogens onto polysiloxanes
and polyacrylate's thereby forming thermally reversible side chain liquid crystalline
polymers (Fig. 5.9, SSCLCPs 6 and 7). They reported a variety of liquid crystalline
mesophases including smectic and nematic ones through small variations of the
mesogen and/or the polymeric backbone. These studies were key to the field of
side chain supramolecular polymers because they demonstrated for the first time
the applicability of the noncovalent functionalization strategy in materials science.
Although the majority of the SSCLCPs reported in the literature are based on a
single type of noncovalent interaction, Bazuin and Sallenave (2007) reported the
application of multiple noncovalent interactions in side chain supramolecular poly-
mers to form functional materials. They used poly(pyridylpyridinium dodecyl metha-
crylate) bromide with terminal pyridyl groups along the side chains as hydrogen
bond acceptors that were proximal to an ion pair at the polymeric scaffold to
anchor a series of phenolic mesogens to the scaffold by using single-point hydrogen
bonding interactions (Fig. 5.9, SSCLCP 8). Bazuin and Sallenave showed that the
hydrogen bond complexation of the mesogens onto the polymer scaffold was suc-
cessful, leading to the formation of SSLCPs that exhibited well-defined thermotropic
