Consideration on formation mechanism of aromatic polyamide hollow spheres prepared by reaction-Induced phase separation

J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1966-1974 Formation mechanism of poly(1,4-phenylene-5-hydroxyisophthalamide) hollow spheres prepared by the reaction-induced phase separation during polymerization was considered from the view points of eliminated small molecules, polymer structure, and cross-linking reaction. Water was the most desirable to form gas-bubbles and rigid polymer structure was also needed for the rapid solidification of droplets. Further, the formation of the cross-linked skin layer was important to encapsulate gas-bubbles in the droplets.

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 gas-bubbles 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.