Chemistry Reference
In-Depth Information
PANI can be obtained. Tiwari et al. [
203
] prepared an electrical conducting guar
gum-based polymer through the graft copolymerization reaction of guar gum with
aniline using APS as the initiator. The features of gum were kept and an electrical
conductivity of 1.6
10
2
S/cm was reached at room temperature. This work
group also synthesized AG-g-PANI copolymer, and its cyclic voltammogram
showed three anodic peaks at 0.20 V, 0.58 V, and 0.64 V along with two cathodic
peaks at 0.50 V and 0.40 V, and the electrical conductivity is dependent on the ratio
of aniline to AG, temperature, and pH value. Besides, the other monomer such as
pyrrole was also grafted onto biopolymer collagen and shows better electrical
properties [
204
,
205
], but rare research is regarded on its graft reaction with gum.
5.6.8 Stimuli-Responsive Property
Many natural gums, such as PSY and XG, have stimuli-responsive capability when
it suffers external stimuli such as pH value and electrolyte because they have
functional groups -COOH or -SO
3
2
. The responsive mechanism is the transform
between -COOH and -COO
groups with the change of external pH values. When
the pH value is lower (acidic condition), the -COO
was changed as -COOH
groups, and the gum may generate volume change and a responsive behavior
occurred. Based on these characters, many stimuli-responsive materials were
designed, such as cross-linked XG [
206
,
207
], PSY [
208
], CG [
209
], and SA
[
210
]. But the stimuli-responsive capacity is weak because of the limited functional
groups. The graft copolymerization of gum may introduce various types and
numbers of functional groups, and the intrinsic responsive property can be
enhanced or new responsive properties were introduced. For example, the intro-
duction of temperature-sensitive groups such as isopropyl acrylamide, dimethyl
formamide may bring the gum with temperature-responsive properties.
5.7 Applications of Gum-g-Copolymers
Graft copolymerization of gums with vinyl monomers or other functional
monomers may introduce new groups on the gum backbone to form a comb-type
structure or form a three-dimensional network structure by adding slight cross-
linker. The introduced groups or branch chains on the gum backbone may alter its
charges, mobility, flexibility, hydrophilic or hydrophobic properties, molecular
weight, and so on, and thus, the colloidal properties, complexing capacity for
metal ions, and water absorbing were obviously improved, or the new function
derived from the grafted chains was presented.
