Comparison of the properties of thermotropic liquid crystalline copolyesters containing different disymmetrical units

Abstract

SynopsisThe effect of dissymetrical units on the properties of thermotropic liquid crystalline copolyesters based on hydroxyhenzoic acid (HBA) , terephthalic acid (TPA) , and poly (ethylene terephthalate) (PET) units was examined. The dissymmetrical units employed included 2,7-&hydroxynaphthalene (2,7-DHN), 1,4-dihydroxynaphthalene ( 1,4-DHN), and bromo-hydroquinone (Br-HQ). All of these polymers exhibited turbid melts. The flexible PET units lower the melting and/or stick temperature, and between 10 to 20 mol 9% is a critical level to achieve values in the range of 250°C or lower. The copolyesters based on 2,7-DHN have the highest glass transition temperatures and maintain stiffness to the highest temperatures. The properties of each series of copolyesters are discussed in terms of the efficiency of molecular packing. The effects of chemical and physical inhomogeneity are emphasized.