Control of the length of aromatic polyester whiskers

The control method of poly(p-oxybenzoyl) (POB) whisker length is reported, with the main focus being on how to make the length of the whiskers longer. The POB whiskers were prepared by the polymerization of p-acetoxybenzoic acid in LPF ar 330°C. The increase in whisker length is caused by the way oligomer lamellae pile up along the long axis of the needle-like crystals with spiral growth. From the present detailed morphological observations during polymerization, the tip angle of the whiskers is constant at 80° up to a time 10 min, whereas it becomes significantly sharper to 12° at 30 min. This sharpening of the tip angles seems to be highly related to the degree of supersaturation of the oligomers dissolved in solution. In order to depress the sharpening of the tip angle and to extend the steady-state growth for increase of the whisker length, oligomers were added twice into the polymerization system, after 10 min just before the tip angle becomes sharper and then after 20 min. The addition of oligomers extended the steady-state growth period, and the length was increased from 40 μm to 47 μm with the first addition and then to 50 μm with the second addition. The addition of oligomers during steady-state growth gives the most favourable conditions for continuous growth with spiral growth.