Molecular structure of liquid‐crystalline copolyesters of vanillic acid, 4‐hydroxybenzoic acid and poly(ethylene terephthalate)

Thermotropic liquid‐crystalline copolyesters made from vanillic acid (V), 4‐hydroxybenzoic acid (B) and poly(ethylene terephthalate) (E) were examined by 1H‐NMR and GPC investigations. Nine possible diads could be identified and assigned. The sequence distribution of V/B/E copolyesters tends to change from random to block with an increase of B content in the copolyesters. The sequence distribution also varies slightly with catalyst concentration and polycondensation time. GPC results suggest that the V/B/E copolyesters have narrower molecular weight distribution (MWD) than B/E copolyesters. The MWD of the copolyesters narrows gradually with increasing V content from zero to 5 mol‐%. The GPC chromatograms of the most V/B/E copolyesters show double peaks, which is different from the single peak of the GPC chromatograms of the B/E copolyesters.