Fabrication of poly(p-oxycinnamoyl) needle crystals by using hydrodynamically induced crystallization during solution polymerization

Morphology control of poly(p-oxycinnamoyl) (POC) was studied to overcome the poor processability and microspheres were prepared by the self-organizing polycondensation of (E)-4-acetoxycinnamic acid (ACA) in aromatic solvent at 320°C without stirring. The work reported investigated the fabrication of POC needle crystals by hydrodynamically induced crystallization during polymerization of ACA. Polymerizations of ACA were carried out in a cylindrical vessel equipped with a stirring bar at a concentration of 1.5% under stirring with different speed (γ) of 300, 700 and 1100 rpm. Microspheres were obtained at γ of 300 rpm via liquid-liquid phase separation. In contrast to this, morphology was drastically changed from sphere to needle at γ of 700 and 1100 rpm These needle crystals were obtained with the yield of 22-27 %, which were 1.0-1.5 μm in length and 1.0-1.5 μm in width. The purely laminar flow in the cylindrical vessel at low stirring speed changed to Taylor vortices with the increase of γ and this brought about the huge concentration of oligomers along to the circular flow leading to the crystallization to form the needle crystals.