CRYSTALLIZATION AND MELTING BEHAVIOR OF SEGMENTED THERMOTROPIC POLYMERS .3. ANALYSIS OF 2 POLYESTERS BASED ON 4,4'-(ALKANEDIOYLDIOXY)DIBENZOYL DICHLORIDES AND HYDROQUINONES

A differential scanning calorimeter has been used to investigate the c rystallization and melting behaviour of two segmented nematic polyeste rs based on 4,4'-(alkanedioyldioxy)dibenzoyl dichlorides and hydroquin ones. Isothermal crystallizations from the nematic melt have been carr ied out on both samples. The results are discussed in terms of variati on of the successive melting profiles as a function of various paramet ers, such as the crystallization temperature and time and, in more det ail, the conditions of the preliminary treatment in the nematic state. The complex melting behaviour evidenced by the polyesters can be just ified on the basis of a new scheme, introduced in our previous paper, which accounts for the slow evolution of the nematic melt towards its thermodynamic equilibrium. Above the crystal-nematic transition a cert ain registry of neighbouring chains persists in the melt, which become s poorer and poorer upon increasing temperature and time and eventuall y disappears when equilibrium is attained. These results raise some fu ndamental questions on the ability of thermotropic polymers to crystal lize from the nematic melt and underline that a careful adjustment of the process parameters must be achieved to obtain reproducible results and to control the final properties of the material.