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

✍ Scribed by Hans R. Kricheldorf; Andreas Gerken; Bakhodir Yulchibaev; Christian Friedrich

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 209 KB
• Volume: 38
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(20000601)38:11<2013::aid-pola100>3.0.co;2-p

✦ Synopsis

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.