Chemistry Reference
In-Depth Information
oxide) with acylated adenine and cytosine nucleobases. The film forming, solidlike
properties of the films were attributed to the weak self-association of the adenine
and cytosine groups (,5M
21
), in concert with phase separation, which increased
the hydrogen bonding association via concentration of the hydrogen bonding units.
Rheological and X-ray scattering data studies on the adenine-functionalized
polymer indicated the formation of stacks of the benzyl protected adenine units
showing the presence of p stacking, which diminished on heating above 70 8C.
Blockage of the hydrogen bonding properties via alkyl substitution at the hydrogen
bonding (NH) protons resulted in reversion of the functional polymer to a liquid
state. The protected cytosine containing polymers did not exhibit p-stacking
interactions, which were likely due to the bulky aliphatic tert-butyl containing acyl
group, but they exhibited gel-like behavior in rheological studies.
Binder et al. (2005) compatibilized blends of polyisobutylene and a bisphenol A
containing poly(ether ketone) using telechelic complementary hydrogen bonding.
A thymine and diaminopyridine hydrogen bonding pair with an association constant
near 800 M
21
was employed. This resulted in microphase separation as observed
from TEM and SAXS. From variable temperature SAXS studies, the blend was
stable up to 250 8C, at which point the poly(ether ketone) phase reached the T
g
and macrophase separation occurred. A stronger Janus wedge and barbituric acid
hydrogen bonding pair with an association constant near 10
4
210
6
M
21
resulted in
stability of the blend to nearly 80 8C above the poly(ether ketone) glass transition
(Fig. 4.13).
Castellano and coworkers (2000) developed a calixarene with four terminal
urea groups in a radial, cone-shaped geometry (Fig. 4.14). The self-complementarity
of this hydrogen bonding calixarene exhibited association constants of 10
6
210
8
M
21
and required a central solvent molecule as a space filling guest (either o-
dichlorobenzene or chloroform). The strong hydrogen bonding of ditopic calixarenes
Figure 4.13 Compatibilization of poly(ether ketone) with poly(isobutylene) using Janus
wedge hydrogen bonding (Binder et al. 2005).
