Chemistry Reference
In-Depth Information
replication and transcription in DNA and reactions in enzymes and it is integral to
many molecular recognition events in living organisms. One goal of modern
science is to incorporate such functionality and dynamics into synthetic materials.
In the case of DNA, hydrogen bonding performs in concert with numerous other
noncovalent interactions such as electrostatic interactions and p-p stacking
(Vanommeslaeghe et al. 2006) to yield the double helix structure and to give DNA
its dynamic properties.
Numerous analytical tools are useful in the study of hydrogen bonding phenom-
enon. Fourier transform IR (FTIR; Kyogoku et al. 1967b) and NMR (Fielding
2000) techniques as well as UV visible (Lutz, Thunemann, Rurack 2005) are
useful for determining association constants or observing association phenomena.
Advanced techniques are necessary for the measurement of very high association
constant systems (S¨ntjens et al. 2000). Rheology (M¨ ller et al. 1996; Yamauchi,
Lizotte, Hercules, et al. 2002) and mechanical analysis (Reith et al. 2001) are
useful for determining the influence of hydrogen bonding interactions on thermal
and mechanical properties, whereas microscopy [transmission electron microscopy
(TEM), atomic force microscopy (AFM)] is primarily useful for studying changes
in morphology. Solution rheology is a particularly useful tool for hydrogen
bonded systems because of the ability to introduce solvents of varying dielectric con-
stants and to study the hydrogen bonding interaction as a function of concentration
(Sijbesma et al. 1997; McKee et al. 2004). Light scattering techniques (dynamic
light scattering, static light scattering) are often used to characterize micellar or aggre-
gate structures resulting from hydrogen bonding associations in solution (Liu and
Jiang 1995; Liu and Zhou 2003).
4.2.2. Performance Advantages of Hydrogen Bond
Containing Polymers
Reversibility of the hydrogen bond confers unique properties to polymeric and supra-
molecular materials. In supramolecular science, reversible bonding is important
because it allows the self-assembly process to occur. Molecular recognition and
self-organization are hailed as the mechanisms of supramolecular growth (Kato
1996). Controlled geometric placement of hydrogen bonding groups leads to efficient
molecular recognition, which is optimized through self-organization. Furthermore,
the directionality of the hydrogen bond assists in the construction of supramolecular
structures because random orientations of hydrogen bonding associations leading to
disordered networks are not favored. In the field of polymer processing, thermorever-
sibility is of interest because of the promise for lower melt viscosities of hydrogen
bond containing polymers. Thus, a lower molecular weight hydrogen bonding
polymer could potentially afford mechanical properties approaching those of a
higher molecular weight nonfunctional polymer over a short time scale and yet
exhibit lower melt viscosity when heated above the dissociation temperature of the
hydrogen bonding groups (Yamauchi, Lizotte, Hercules, et al. 2002; Yamauchi
et al. 2004). The hydrogen bonding polymer would exhibit a higher apparent molecu-
lar weight at room temperature than it actually possessed.
