Large Optical Rotatory Power and Light Modulation in Polylactic Acid Film

与无机低分子量晶体相比，其分子含有不对称碳原子并具有螺旋取向的聚乳酸长期以来一直被期望在固态下表现出具有显着高旋光度的旋光性（OA）。我们研究了聚-L-乳酸（PLLA）和聚-D-乳酸（PDLA）薄膜的OA和光调制（LM）性能，其中高阶结构是通过锻造工艺实现的。我们证实了PLLA和PDLA膜分别具有左旋和右旋能力。PLLA薄膜的旋光率ρ为7200°/mm，约为α-石英的300倍。这个ρ值是一个杰出的记录。我们可能不可能确定影响ρ值的每一个因素，因为有太多的因素。因此，我们选择了两个可以想象的重要因素，分子量M_w和异构体（D型）含量（ID）。ρ随ID的增大而减小，ρ随M_w的减小而减小。因此，我们发现ID和M_w是影响ρ值的重要因素。PLLA薄膜的高次结构受ID和M_w的影响较大。也就是说，PLLA样品前所未有的大ρ是由于其更高阶的结构。基于上述结果，我们得出结论，这种锻造技术是有用的，用于生产具有受控的高阶结构的薄膜。然后，我们确认了高达10 MHz的PLLA膜的LM。由于PLLA膜提供了快速响应，我们相信使用更多改性的PLLA样品可以实现GHz范围内的LM速度。

Polylactic acid, molecules of which contain asymmetric carbon atoms and have a helical orientation, have long been expected to exhibit optical activity (OA) with significantly high optical rotatory power in the solid state, compared with inorganic low-molecular-weight crystals. We examined the OA and light modulation (LM) properties of poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) films of which the higher order structure is achieved by a forging process. We confirmed that the PLLA and PDLA films possess levorotatory power and dextrorotatory power, respectively. The optical rotatory power ρ of the PLLA film is 7200°/mm which is approximately 300 times greater than that of α-quartz. This ρ value is an outstanding record. It may be impossible for us to identify every factor affecting the value of ρ because there are so many. Thus, we selected two conceivably important factors, a molecular weight M_w and isomer (D-type) content (ID). ρ decreases with increasing ID. ρ also decreases with decreasing M_w. Thus, we found that ID and M_w are important factors affecting the value of ρ. The higher order structure of PLLA films is greatly influenced by ID and M_w. Namely, the unprecedented large ρ of the PLLA sample is due to its higher order structure. Based on the above results, we conclude that this forging technology is useful for producing films with a controlled higher order structure. We then confirmed LM of the PLLA film up to 10 MHz. Since the PLLA film provides a fast response, we believe that a LM speed in the GHz range is possible using a more modified PLLA sample.