Development of New Technology for Control of Length of Aromatic Polyester Whiskers

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The poly (p-oxybenzoyl) (POB) whiskers are prepared by the polymerization of p-acetoxybenzoic acid in liquid paraffin at 330ﾟC.The polymer chains are aligned to the long axis of the whisker and it shows the single crystal nature. Therefore, this whisker has a high potential for applications of structural materials, devices and so on. In this project, we aim to develop the control method of the POB whisker length.It is revealed that the formation mechanism of the whiskers includes the following steps ; 1) oligomers are precipitated by crystallization to form the lamellae, 2) the lamellae pile up along the long axis of the needle-like crystals with a spiral growth caused by screw dislocation, 3) DP increases by post-polymerization in the interlamellar regions. In this mechanism, the tip angle of the whiskers is constant at 80ﾟ up to 20min, whereas it becomes significantly sharper to 7-8ﾟ at 30 min. The growth rate of the step at the small radius of curvature decrease due to the increase of the strain energy of secondary nucleation, and therefore the spiral appears to rotate with uniform angular velocity under a steady state within 20 min. It is necessary to depress the sharpening and lengthen the period of the steady growth increase the length. In order to compensate the decreased concentration of oligomers, oligomers are added into the polymerization system after 15 min.just before when the tips angle becomes sharper. The addition of oligomers lengthens the steady growth period from 20 min.to 30 min., and then the length increases 16%. The length increases continuously by the second addition and the whiskers having the 32% increased length are obtained. The result show the new method for the control of the whisker length.