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

对乙酰氧基苯甲酸在液体石蜡中于330 ℃进行聚合，制得了聚对羟基苯甲酰基（POB）晶须，聚合物链沿晶须长轴方向排列，呈单晶结构。因此，这种晶须在结构材料、器件等方面具有很大的应用潜力，本项目旨在开发POB晶须长度的控制方法，揭示了POB晶须的形成机理包括以下几个步骤：1）通过结晶使低聚物沉淀以形成层状结构，2）片层沿针状晶体长轴沿着方向堆积，螺旋位错引起螺旋生长; 3）片层间发生后聚合，聚合度增加。在此机制下，晶须的顶角在20 min内保持不变，而在30 min时变得明显尖锐，达到7-8 μ m。由于二次成核应变能的增加，小曲率半径处的台阶生长速率降低，因此，在20 min内，螺旋线在稳定状态下呈现匀速旋转，需要抑制螺旋线的尖锐化，延长螺旋线稳定增长的时间增加长度。为了补偿低聚物浓度的降低，在15分钟后，就在尖端角变得更尖锐之前，将低聚物加入聚合体系中。低聚物的加入延长了稳定生长期，从20min.to30分钟，然后长度增加16%。通过第二次添加，晶须的长度继续增加，并且获得具有增加的32%长度的晶须。结果表明，该方法为晶须长度的控制提供了新的途径。

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.