Biomedical Engineering Reference
In-Depth Information
H
C
H
2
C
OH
R
O
R
O
O
OH
HO
R
¢
C
O
OH
C
OH
O
O
R
¢
R
¢
O
CH
2
C
OH
O
O
*
R
*
C
H
n
(a)
CH
2
O
R
¢
O
C
H
2
O
(CH
2
)
3
R
O
O
O
(CH
2
)
4
*
C
H
*
OH
OH
n
O
R
OH
O
O
H
2
O
(CH
2
)
3
O
OH
R
(CH
2
)
3
OH
OH
OH
O
(CH
2
)
3
R
OH
OH
OH
(b)
1.14
POE
III
: (a) synthesis and (b) hydrolysis.
because of hydrolysis for POe iii polymers. However, the synthesis presents
some problems such as long reflux times and ethanol removal in order to
obtain high molecular weight. It is difficult to obtain reproducible results
and a control on molecular weight, and thus POe iii were discarded, even
if they had shown a very good ocular compatibility.
Synthesis of POE IV materials is similar to POE II reaction, but mono/
dilactide or mono/diglycolide are included in the backbone (Fig. 1.15). These
fragments can be considered as 'latent acids' because hydrolysis of POe iV
polymers produces lactic acid or glycolic acid which act as catalysts for the
hydrolysis of ortho ester linkages. The advantage of these polymers is the
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