Biomedical Engineering Reference
In-Depth Information
S
2
O
2-
+ HSO
-
SO
2-
+ ∗ SO
-
+ ∗ HSO
3
∗ SO
-
+ HSO
-
SO
2-
+ ∗ HSO
3
∗ HSO
3
+ Chitosan
Chitosan ∗ + H
2
SO
3
Chitosan ∗ + M
Chitosan - M ∗
∗ HSO
3
+ M
HSO
3
- M ∗
Figure 1.22
Oxidation-reduction initiating reaction mechanism by persulfate.
of chitosan and methyl methylacrylate in water solution [93]. The mechanism is probably as
in Figure 1.23. The reaction is graft polymerization of chitosan with free radicals and
monomers.
A research paper published in 1979 claimed that tributylborane can be used as an initia-
tor for the graft polymerization of chitin [94]. The mechanism includes the following steps:
first, water diffuses into the main chain of chitin to solvate chitin; second, solvated chitin
forms a complex with tributylborane; and third, monomer diffuses into chitin and reacts
with the complex to generate macromolecular free radicals for initiating graft polymeriza-
tion. Tributylborane is not a universal initiator.
Azodiisobutyronitrile is a common initiator for free radical polymerization and can also
be used for initiating graft polymerization of chitosan and an alkyl monomer [95]. In a het-
erogeneous reaction, acrylonitrile and methyl methylacrylate can only graft aminos of
chitosan if the initiator is azodiisobutyronitrile, and the product is insoluble in dilute acid.
Only if the monomer is ethenyl ethanoate, graft polymerization will occur at sites other
than amino and the product is soluble in 2% acetic acid. In a homogeneous reaction, ethenyl
ethanoate can only graft aminos, and the solubility of the product in dilute acid is limited.
Radiation is also used for initiating graft polymerization. To date, only γ-rays of
60
Co can
be used for graft polymerization of chitin and chitosan.
Maximal percentage conversion and percentage grafting can be obtained when chitin
and styrene are irradiated by γ-rays at 30°C in water. This proves that water can permeate
into chitin for solvating, which damages the hydrogen bonds between chitin molecules
and increases the diffusivity of styrene, so that the reaction becomes easier [96]. High
percentage grafting of chitosan powder and styrene can be obtained when styrene is
turned into a 50% water solution. Differently, chitosan film can be grafted without solvent,
H
2
O
2
+ Fe
2+
∗ OH
+ OH
-
+ Fe
3+
∗ OH
+ Fe
2+
OH
-
+ Fe
3+
H
2
O
+ ∗ OOH
∗ OH
+ H
2
O
2
∗ OOH
+ H
2
O
2
∗ OH
+ Chitosan
∗ OH
+ O
2
+ H
2
O
Chitosan ∗ + H
2
O
Figure 1.23
Oxidation-reduction initiating reaction mechanism by the H
2
O
2
-Fe system.
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