Hollow spheres of aromatic polyamide are obtained by the reaction-induced phase separation during polymerization of 5-hydroxyisophthalic acid and 1,4-phenylene diamine in an aromatic solvent at a concentration of 1-2% at 320 C without stirring. The hollow sphere has a dimple hole and the diameters of the hollow spheres are 3-4 lm. The droplets are initially generated via liquid-liquid phase separation and then rigid crosslinked network structure formed the rigid skin layer on the surface of the droplets. The solidification of the droplets occurred owing to the further polymerization in them with maintaining the morphology to form the hollow spheres. The hollow spheres exhibit outstanding thermal stability. 14 Although the rigid polyimides exhibit poor tractability, hollow spheres can be prepared using the soluble precursor poly(amic acid)s. However, many of other aromatic polymers show neither fusibility nor solubility owing to their rigidity and it is too difficult to control the morphology precisely.
Hollow spheres of poly(1,4-phenylene-5-hydroxyisophthalamide) had been obtained by the reaction-induced phase separation during polymerization of 5-hydroxyisophthalic acid and 1,4-phenylene diamine in an aromatic solvent. In this study, formation mechanism of the hollow spheres was considered from the view points of eliminated small molecules, polymer structure, and cross-linking reaction. With respect to the eliminated small molecules, water was the most desirable to form gasbubbles in droplets compared with methanol and acetic acid, due to the insolubility into the polymerization system. Rigid polymer structure was also needed to prepare hollow spheres owing to the rapid solidification of droplets. Further, phenolic hydroxyl group in 5-hydroxy-1,3-phenylene moiety caused the ester-amide exchange reaction to form cross-linked skin layer in the droplets. The efficient formation of the skin layer was important to encapsulate gas-bubbles in the droplets, resulting in the formation of hollow structure.
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