Semi-aromatic polyamides containing fluorenyl pendent toward excellent thermal stability, mechanical properties and dielectric performance

Semi-aromatic polyamides (SaPAs) combining each advantages of aliphatic and aromatic polyamides received ever-increasing development in both academia and industrial circles. In this work, four kinds of SaPAs with fluorenyl pendent and different length of aliphatic spacers, named P–FPB, P–FPH, P–FPO and P–FPD respectively, were designed and synthesized via the aromatic nucleophilic substitution (SNAr) polycondensation. The effects of both the rigid pendent and flexible methylene (4, 6, 8, 10) spacers on the comprehensive properties of the SaPAs were comprehensively investigated. At the presence of the rigid fluorenyl pendent and the intermolecular π–π stacking thereof, the resulting SaPAs exhibited enhanced glass transition temperature (Tg), thermal stability, solubility in typical organic solvents and mechanical properties compared with the commercially available 6T based SaPa. Also with increasing the number of the methylene units of the SaPAs, their Tg, Vicat softening temperature, tensile strength and modulus gradually decreased; while the initial decomposition temperature and impact strength anomalously increased. Rheological investigations and solubility tests further confirmed that the resulting SaPAs were suitable for processing either in melt or in solution. In addition, these polyamides displayed favorable dielectric properties for potential availability in electric and electronic applications.