High-performance all-aromatic liquid crystalline esteramide-based thermosets

Abstract

We have synthesized and characterized a new family of nematic all-aromatic polyesteramide thermosets based on 6-hydroxy-2-naphthoic acid (HNA), terephthalic acid (TA), and 4-acetamidophenol (AAP). In order to incorporate a high concentration of the amide-based monomer (AAP), the melt transition ( T K-N) and melt viscosity had to be lowered in order to maintain melt processable intermediates. Precursor thermoplastic reactive oligomers, end-capped with phenylethynyl functionalities, were prepared using standard melt condensation techniques with a target M n of 1000–9000 g mol−1. The reactive oligomers with 20–30 mol% AAP could easily be processed into films, and the films exhibit good tensile properties in terms of tensile strength (70–80 MPa) and elongation at break (7–10%). A glass transition of 191°C could be obtained when a 1000 g mol−1 oligomer (HNA/TA/AAP(20)–1 K) was thermally cross-linked. When the AAP concentration reaches 35 mol%, the rigidity of the backbone and the hydrogen bonding interactions are enhanced, which make HNA/TA/AAP(35) polymers difficult to process.

Chemistry and Rheological Behavior of Cross-Linked Liquid Crystal Polyarylate with a Mixed End-Capping Strategy

“…The phenylethynyl group (PEPA) could be cured at 370 °C but is kept latent during polycondensation at ∼300 °C, which had successfully terminated various aromatic thermoplastic polymers (i.e., LCP and polyesterimide) in the past 2 decades. − This strategy not only effectively reduced melting point ( T m ) and improved processability of thermoplastics but also significantly enhanced their thermomechanical properties with the formation of cross-linked networks through the cure reaction of PEPA. For instance, PPTA exhibited a glass transition temperature ( T g ) of 267 °C and a T m of 610 °C, which made it rather intractable that the polymer in fact decomposed before it melted.…”