Tuning the Pendent Groups of Semiaromatic Polyamides toward High Performance

The construction of novel semiaromatic polyamides (SaPAs) combining all advantages of aliphatic and aromatic polyamides is of particular importance in both academia and industrial circles. To study the effect of different pendent groups on the comprehensive properties of SaPAs, three kinds of SaPAs with different pendent groups were designed and prepared by the aromatic nucleophilic substitution polycondensation, named as P-PAH (dimethyl-), P-PEPH (methylphenyl-), and P-DPMPH (diphenyl-). All of these polyamides exhibited a relatively high molecular weight with narrow molecular weight distribution. It was found that the chain conformation of P-PEPH was significantly different from those of P-PAH and P-DPMPH due to the formation of the helical structures caused by the asymmetric methyl and phenyl pendent groups, which was testified by computational simulation. Meanwhile, SaPAs with phenyl pendent groups (P-PEPH and P-DPMPH) exhibited an interaction between molecular chains due to π–π stacking, as proved by wide-angle X-ray diffraction (WAXD) results. With an increase in the content of the phenyl pendent groups, their glass-transition temperatures (Tg) increased gradually from 135.6 to 156.5 °C and the initial decomposition temperatures (T5%) also increased. Rheological investigations and solubility tests showed that these polyamides were suitable for processing either in melt or in solution. The expected mechanical properties of P-PEPH were also obtained due to the unique chain conformation and π–π stacking. Taking these advantages, this kind of novel SaPAs exhibited potential availability in versatile applications.