Preparation of helical crystals of aromatic poly(ester-imide) and on-off switching of helix formation

Preparation of poly[4-(5-oxy-1,3-dioxoisoindoline-2-yl)benzoyl] (PODB) crystals, which was an intractable aromatic poly(ester-imide), was examined by means of reaction-induced crystallization of oligomers during the polymerization. Highly crystalline PODB helical ribbons were obtained by the polymerization of N-(4-carboxyphenyl)-4-acetoxyphthalimide in aromatic solvent at 280–330 °C at a concentration of 0.5–1.0%. The PODB molecules aligned along the long axis of the helical ribbon. The pitch of the helix increased with the polymerization temperature and it could be controlled from 320 nm to 1.3 μm. Further, the fibrillar PODB crystals comprised of the helical and the non-helical blocks were prepared by the on-off switching of the helical morphology with the changing the temperature and the concentration of the polymerization. These results provided the methodology for the morphology control of polymer crystals.