1. Chemical and crystal structure of aromatic PCLs

As we have seen, PCL molecules like CLs must contain rigid segments longer than 20 Å (2 nm) [1] .

In PCL, these segments are themselves made up of rigid subunits (monomers) connected by rigid bonds.

The most common subunits (monomers) are aromatic, like benzene or naphthalene, with para-oriented 1.4 bonds for benzene and 1.4 and 2.6 bonds for naphthalene.

Although equally rigid, 1,4-parasubstituted cyclohexane is not used due to its thermal instability. Many rigid bonds are possible to link benzene or naphthalene rings together.

The main monomers used in the manufacture of liquid crystal polyesters are shown in figure