Effects of monomer structures on the evolution of liquid-crystal texture and crystallization during thin-film polymerization

We investigated in situ the effects of monomer structures on the formation and evolution of liquid-crystal texture and crystallization during thin-fil m polymerization of a series of liquid-crystalline and crystalline polymers . The monomers used in this study consisted of 2,6-acetoxynaphthoic acid (A NA), p-acetoxybenzoic acid (ABA), acetoxy acetanilide (AAA), and isophthali c acid (IA). The polycondensation reactions were conducted on the heating s tage of a polarizing microscope. The formation of liquid crystallinity was found to be strongly dependent on the straight-monomer structures of ANA an d ABA and their percentages as well as the reaction temperature. For the AN A/AAA/IA and ABA/AAA/IA reaction systems, the critical straight-monomer con tent (ANA or ABA) existed to form the liquid-crystalline (LC) state. Intere stingly, the critical content to form liquid crystallinity decreased with a n increase in the reaction temperature. Above the critical content, the app earance of a defective LC phase and the annihilation of disclinations were observed during the polycondensation reactions. The number of defects decre ased with increasing reaction time through annihilation. The annihilation r ate increased whereas the defect density decreased with increasing straight -monomer content. For the same molar ratio, the reaction system containing ANA had a faster annihilation rate than that containing ABA. Below the crit ical content, crystalline polymers were formed. Nucleation and crystal grow th were observed during the reactions, and the rate of crystal growth decre ased with increasing ANA or ABA content. For the systems having the same mo lar ratio of ANA or ABA, the ANA/AAA/IA system had a higher tendency to yie ld the LC phase than the ABA/AAA/IA system because ANA has a longer mesogen ic unit. (C) 1999 John Wiley & Sons, Inc.