New polymer syntheses. 102. Aspirin‐modified LC polyesters based on PET and 4‐hydroxybenzoic acid

Abstract

Four series of liquid-crystalline copolyesters were prepared by the transesterification of poly(ethylene terephthalate) (PET) with 4-acetoxybenzoic acid (4-ABA) or mixtures of 4-ABA and acetylsalicylic acid (ASA). Two series consisted of 30 mol % PET, and the other two series consisted of 40 mol % PET. The molar ratio of 4-HBA and ASA was varied in all four series from 0 to 25 mol %. One 30% PET series and one 40% PET series were prepared with the addition of acetic acid, which caused a more perfect randomization of the sequence but yielded slightly lower molecular weights. The incorporation of ASA reduced the crystallinity, which vanished completely at a salicylic acid (SA) content greater than 10 mol %. SA also reduced the stability of the nematic phase, but all the copolyesters were thermotropic up to a 20 mol % SA content. Furthermore, the molecular weights decreased with the increasing incorporation of ASA. Despite this negative trend, the melt viscosity and the storage and loss moduli passed a maximum between 5 and 10% SA. Obviously, the incorporation of SA favored the formation of entanglements. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2013–2022, 2000