2. Synthesis and processing of aromatic PCL

• Summary

  Aromatic liquid-crystalline polyesters cannot be synthesized in the same way as PET and PEN.

  This is because hydroxyl groups are not reactive enough to guarantee a high conversion rate to ester bonds during direct polycondensation of diacids, dialcohols and hydroxyacids with one another.

First, the hydroxyl groups are reacted with acetic anhydride to form acetate and acetic acid, which is then removed (figure 4 a). The acetate thus formed is then reacted with the carboxyl groups under atmospheric pressure, in the presence of a neutral gas, and at increasing temperature up to around 320 C. This produces a low-molecular-weight oligomer (M _n " 2,000)....