Morphology control of poly(azomethine ester) by using reaction-induced oligomer phase separation

Spindle-like crystals of poly(azomethine ester) (PAME) were formed by the polymerization of 4-(4-acetoxybenzylidenamino)benzoic acid (ABBA) in liquid paraffin (LPF) at 300°C via reaction-induced crystallization of oligomers. But the trace of lamellae stacking structure was observed on the surface of crystals due to the lack of post-polymerization between the oligomers in the crystals. In order to induce the crystallization at 350°C to accelerate the post-polymerization, the polymerization of ABBA was carried out in the mixed solvent of LPF and aromatic solvent. This polymerization afforded the fibrillar crystals having smooth surface. One-pot polymerization of 4-acetoxybenzaldehyde and 4-aminobenzoic acid yielded ribbon-like PAME crystals besides spherical precipitates. These ribbon-like crystals showing the larger width than the fibrillar crystals prepared from ABBA were formed by the crystallization of oligomers through the stepwise formation of azomethine linkage and ester linkage during the elevated temperature polymerization. These crystals possessed quite high crystallinity as well as the fibrillar crystals. The morphology of PAME was controllable by means of precipitation during solution polymerization.