Crystallization of Polymers Induced by Supercritical Fluids

用配备高压钻石ATR池的FT/IR光谱仪测量了超临界二氧化碳诱导聚乳酸的结晶速率。1266 cm~(-1)~(-1)的吸光度变化与X射线衍射法得到的结晶度有关。由于溶质在聚合物中的扩散速度通常较小，且结晶过程伴随着溶质的吸附，因此很难从实验观察中提取结晶速率。然而，本文使用的ATR法只能测量结晶速率，因为这种方法可以使聚合物样品变薄(约10μm)，并且吸附平衡达到小于9 S。为了确定这一点，我们测量了4种厚度(10，50,100和250μm)的样品的结晶速率。100和250μm样品的吸光度变化率随厚度的增加而减小，而10μm和50μm样品的吸光度变化率与吸光度变化率的关系不明显，因此我们选择了10~20 mm样品，在1和2 Mpa的CO_2处理压力下，X射线衍射仪没有观察到结晶，而FT/IR观察到了结晶。这意味着可能存在细小的微晶，而这是用X射线衍射仪无法检测到的。对CO_2处理后的样品进行了DSC测试，以确定其存在。晶化温度随处理压力的增加而降低。这一结果意味着细小微晶的存在。通过对吸光度变化的测量，明确了结晶机理。该机制由两个步骤组成，首先是细小的微晶迅速形成，然后开始生长。

Crystallization rate of polylactide induced by supercritical carbon dioxide was measured with a FT/IR spectrometer equipped with a high-pressure diamond ATR cell. Absorbance change at 1266 cm^<-1> was related with crystallinity obtained from X-ray diffraction (XRD). It is hard to extract the crystallization rate from experimental observation, because solute diffusion rate in polymer is usually small and the crystallization follows sorption of the solute. The ATR method used in this work, however, will measure only the crystallization rate, because polymer sample can be thinner (about 10 μm) in this method and sorption equilibrium accomplished less than 9 s. The crystallization rate of four kinds of sample thickness (10, 50, 100, and 250 μm) was measured to make sure this. While the rate of the absorbance change decreased with increasing the thickness of the 100 and 250 μm sample, sample thickness dependence on the rate did not be observed in the sample thickness of 10 and 50 μm. Therefore, we used the samples of thickness from 10 to 20 μm. The crystallization did not be observed with XRD at CO_2 treatment pressure of 1 and 2 MPa, whereas the crystallization was observed with FT/IR. This observation means possibility of small crystallite existence, which can not be detected with XRD. DSC measurement of CO_2 treated sample was carried out to make sure the existence. The crystallization temperature decreased with increasing the increasing the treatment pressure. This result means the existence of small crystallite. The crystallization mechanism was made clear through the absorbance change measurements. The mechanism consists of two steps, at first small crystallite rapidly forms and then growth of the crystallite begins.