Biomedical Engineering Reference
In-Depth Information
O
O
O
O
O
O
O
O
Reflux at 150
o
/30 min
±Coordination Catalyst
HO
C
R
C
OH
+
H
3
CC
O
C
CH
3
H
3
CC
OC
R
C
O
C
CH
3
m
O
O
O
O
180
o
C/<1mmHg
~90 min
H
3
CC
OC
R
C
O
C
CH
3
n
O
O
O
O
O
O
O
O
Et
3
N/O
0
C
x
HO
C
R
C
OH
+
y
Cl
C
R'
C
Cl
CH
2
Cl
2
CR
C
O
C
R'
C
O
+Et
3
N:HCl
y
x
O
O
O
O
Hexane.DMF
or CH
2
Cl
2
Cl
C
R'
C
Cl
n/2 H
2
O
+
C
R'
C
O
+nHCl
n
O
O
O
O
Dehydration agents
Hexane-DMF or CH
2
Cl
2
HO
C
R
C
OH
C
R'
C
O
n
AC
2
O
(CH
2
)
4
HOOC
COOH
H
3
COC
O
CO
(CH
2
)
4
CO
O
COCH
3
O
CO
(CH
2
)
4
CO
CH
3
COOZn.2H
2
O
O
CO
(CH
2
)
4
CO
n
O
O
O
Scheme 3.1
General synthesis schemes for polyanhydrides.
polymerization in general yielded low molecular weight polymers. A variety of
catalysts have been used in the synthesis of a range of polyanhydrides by melt
condensation. Particularly, coordination catalysts facilitate anhydride interchange
in the polymerization and enhance the nucleophilicity of the carbonyl carbon.
Signifi cantly higher molecular weights in shorter reaction time were achieved by
utilizing cadmium acetate, earth metal oxides, and ZnEt
2
· H
2
O. Except for calcium
carbonate, which is a safe natural material, the use of these catalysts for the pro-
duction of medical grade polymers is limited due to their potential toxicity [7].
Since melt condensation occurs at high temperatures, it is not suitable for
heat-sensitive monomers, which require milder reaction conditions. A variety of
solution polymerizations at ambient temperature have been reported [65, 67].
Polyanhydride formation can be effected at room temperature by dehydrochlo-
rination between a diacid chloride and a dicarboxylic acid. In an attempt to
