Biomedical Engineering Reference
In-Depth Information
and exposure time on graft copolymerization were studied. Grafting was found to increase
with an increase in the initial concentration of monomer. Grafting was also found to
increase up to 80% microwave power and thereafter decrease. Grafted chitosan showed
good solubility at higher pH than chitosan.
2.11.3 Copolymerization via Polycondensation
Condensation polymerization has not been widely used for preparing graft copolymers
of polysaccharides, usually due to susceptibility of the saccharide backbone to high tem-
perature and harsh conditions of the typical polycondensation reactions. However, lactic
acid (LA) was successfully graft copolymerized onto chitosan through condensation
polymerization of d,l-lactic acid in the absence of a catalyst [274,297], which forms a pH-
sensitive hydrogel (
Figure 2.32)
.
The condensation of polylactide has also been achieved
by using the catalyst 4-dimethylaminopyridine, where polylactide was grafted through
the hydroxyl groups phthaloylchitosan. A carbodiimide process of condensation too is
used to link the amino group of chitosan to polylactic acid surface or to a peptide to
improve cell compatibility and adhesion [298] and support the proliferation of human
endothelial cells [274,299].
2.11.4 Cationic graft Polymerization
Some years ago, Yoshikawa et al. [300] showed that grafting reactions onto chitosan can
also be performed by using living cationic polymerization. These authors grafted chitosan
with living poly(isobutylvinyl ether) and poly(2-methyl-2-oxazoline) cation with controlled
molecular weight distribution. In this study, the effect of the molecular weight of living
polymer cation on the mole number of grafted polymer was analyzed. The mole number
of grafted polymer chains was found to decrease with increasing molecular weight of
OH
OH
OH
H
O
O
O
HO
COOH
O
O
O
O
80°C
-H
2
O
O
O
HO
Me
HO
NH
HO
NH
3
+
NH
2
D,L Lactic acid
H
Me
O
HO
COO-
Chitosan
O
O
H
Me
Me
O
n
Phthaloylation
O
OPLLA
O
OPLLA
O
OH
OH
O
O
O
O
O
ALLPO
O
DMSO, Dimetylaminopyridine
O
HO
O
O
O
O
NHCOCH
3
HO
PLLAO
NHCOCH
3
NHPhth
NHPhth
PHC-g-PLLA
Phthaloylchitosan (PHC)
O
O
O
OH
PLLA =
CH
3
n
CH
3
Figure 2.32
Grafting of LA on chitosan.
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