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

以对乙酰氧基苯甲酸为原料，在330℃的温度下，在液体石蜡中聚合制备了聚对氧苯甲酰（POB）晶须。聚合物链沿晶须长轴排列，呈现单晶性质。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。在本项目中，我们旨在开发POB晶须长度的控制方法。结果表明，晶须的形成机制包括以下几个步骤；1)低聚物通过结晶析出形成片层；2)螺旋位错导致片层沿针状晶体长轴堆积，呈螺旋状生长；3)在片层间区域聚合后DP增加。在此机制下，晶须的尖端角度在80 ~ 20min时是恒定的，而在7 ~ 8 ~ 30min时变得明显锐利。在小曲率半径处，由于二次形核应变能的增加，台阶的生长速度减小，因此在20 min内螺旋呈现匀速角速度的稳态旋转。有必要抑制锐化，延长稳定生长期，增加长度。为了弥补低聚物浓度的下降，在聚合体系中加入低聚物15分钟后，就在尖端角变尖之前。低聚物的加入使其稳定生长期由20 min延长至30 min，而后延长16%。经第二次添加，晶须长度连续增加，晶须长度增加32%。结果表明，该方法可以有效地控制晶须的长度。

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.