Biodegradable Polymers Composed of Naturally Occurring- Amino Acids - Biodegradable Polymers - page 111

- alkylene diols [8 - 17, 21, 24, 27 - 35] , dianhydrohexitols [25,
26], and di-, tri, and tetraethylene glycols [35, 36] were used by different authors
for synthesizing TAADs.
The obtained di- or tetra-TAADs are stable compounds. The most of these
monomers were purifi ed by recrystallizing from water or organic solvents. The
yields of pure, polycondensation grade products ranged within 60-90%.

Various aliphatic α , ω

5.2.1.2 Bis - Electrophiles
For successful synthesis of AABBPs with tailored architecture, the selection of
suitable bis - electrophilic monomer(s) is also important - counterpartners of
TAADs. The syntheses of various bis-electrophiles are discussed below as detailed
as possible within the bounds of this chapter.
Dicarboxylic acids HO - CO - A - CO - OH can be incorporated into the PEA back-
bones by means of either dichlorides Cl- CO - A - CO - Cl (dicarboxylic acid dichlo-
ride, DDC) or active diesters R 1 - CO - A - CO - R 1 (dicarboxylic acid active diester, DAD)
as bis-electrophilic monomers (for A and R 1 , see Scheme 5.2 ).
Many DDCs are commercial products. DADs are obtained using three synthetic
methods: (i) by interaction of DDCs with various hydroxyl compounds HOR 1
(activating agents), Scheme 5.2 [14, 15, 20, 24, 25], or by direct interaction of
dicarboxylic acids (ii) with HOR 1 in the presence of various condensing (coupling)
agents, Figure 5.4 [15, 21, 37], or (iii) with various trans - esterifying agents that are
derivatives of HOR 1 , Scheme 5.3 [37] .
All three methods give DADs in a good yield ranged from 60% to 90%.
Monomers for synthesizing PEURs. The third building block of PEURs - carbonic
acid - can be incorporated into the polymeric backbones by means of either bis-
chloroformates Cl - CO - O - D 1 - O - CO - Cl (diol bis - chloroformate, BCF) or active bis -
carbonates R 1 - CO - O - D 1 - O - CO - R 1 (DBCs) as bis-electrophilic monomers (D 1 can
be the same as D in Scheme 5.1).
Diol bis -carbonates (DBCs) can be obtained using two synthetic methods: (i) by
interaction of BCFs with hydroxyl compounds HOR 1 , Scheme 5.4 [38] , or (ii) by
interaction of diols with mono-chloroformates of hydroxyl compounds Cl-CO-
O - R 1 , Scheme 5.5 [39] .
The building block for PEUs, carbonic acid, can be incorporated into the poly-
meric backbones by means of polycondensation using either phosgene (deriva-
tives), or active carbonates (AC) obtained according to Scheme 5.6 or related
compounds [40] .

5.2.2
AABBP s ' Synthesis Methods

PEAs. The synthesis of PEAs on the basis of TAADs can be carried out at a low
temperature via interfacial polycondensation (IP) and solution polycondensation
(SP). The IP and SP reactions proceed according to Figure 5.5 in the presence of
acid acceptor (HCl and/or TosOH).
The selection of the polycondensation method depends on the nature of bis-
electrophilic monomer. The IP is suitable method when DDCs are used.