304 HIGH PERFORMANCE POLYMERS
Partially aromatic PAs can be prepared from t he
acid, instead of the acid chloride in a multi-step pro-
cess. The first steps are conducted as a solid state
polymerization with increasing temperature steps, and
optionally feeding monomers after each reaction step.
The final steps are proceeding as a melt condensation
reaction [8].
Alternatively, instead of the acids, the correspond-
ing esters can be used as starting materials [20].
Esterification of the dicarboxylic acid advantageously
lowers its melting point to a temperature that allows
melting of the acid while minimizing the thermal
degradation. The admixture of the dicarboxylic acid
component and the diamine component in the form of
a melt is thereby facilitated.
Further ...