Chemistry Reference
In-Depth Information
Figure 5.18 Cross-linking profile of poly-CA using the triazine-based cross-linking agent.
Filled symbols denote the elastic modulus (G
0
) whereas empty symbols denote the loss
modulus (G
00
) at a strain value of 0.1. The percentage of the triazine-based cross-linking
agent is based on the cyanuric acid groups attached to the polymer.
bonding interactions with the cyanuric acid groups; thus, each cross-linking agent is
able to bind more than two cyanuric acid groups. However, the wedge-based cross-
linking agent is able to connect only two cyanuric acid groups and forms no true
three-dimensional network, having a continuum. As a result, the network microstruc-
tures of the two polymer networks are markedly different. Hence, when using comp-
lementary hydrogen bonding networks, by choosing the appropriate cross-linking
agent we can obtain a high degree of control over important network parameters
such as the cross-linking density, strength of the cross-links, network microstructure,
and extent of polymer cross-linking.
Polymer Networks Based on Polymer Blends.
The physical combination of two
or more chemically different polymers to yield a hybrid material possessing the desir-
able properties of all the combined polymers is a well-established part of materials
science. However, serious challenges, such as the inherent immiscibility of different
polymers leading to phase separated materials, have to be overcome for materials
applications. Many strategies have been used to minimize interfacial energy and to
reduce the propensity for phase separation, including the use of compatibilizers
and introduction of reactive groups to covalently connect individual polymers
within the blend. One strategy to overcome microphase separation is the use of hydro-
gen bonding interactions. The polymers that need to be blended can be functionalized
with complementary hydrogen bonding functional groups and, when blended either
in solution or the melt, can undergo interchain hydrogen bonding interactions
between the two inherently immiscible polymers, thereby suppressing phase separ-
ation and forming a homogeneous polymer blend (Fig. 5.14c).
Most systems described in the literature rely on fairly weak hydrogen bonding
complexes based mainly on one- or two-point
interactions between functional
