Polymorphic transition in disordered poly(L-lactide) crystals induced by annealing at elevated temperatures
Polymorphic transition in disordered poly(L-lactide) crystals induced by annealing at elevated temperatures
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DOI：
10.1021/ma800343g
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发表时间：
2008-06-24
期刊：
影响因子：
5.5
通讯作者：
Inoue, Yoshio
中科院分区：
文献类型：
--
作者：
Pan, Pengju;Zhu, Bo;Inoue, Yoshio
采用广角X射线衍射仪、傅里叶变换红外光谱仪和差示扫描量热仪研究了不同热处理条件和不同相对分子质量对聚L-丙交酯(PLLA)结晶相变的影响。发现PLLA的无序晶体(α‘晶型)在高温下的热处理过程中转变为α晶型。从α‘到α的转变很大程度上取决于退火期(t(A)：0-1440分钟)和退火温度(T-a：120-160℃)。随着T-a的增大，这种多态转变的进展速度更快。α‘到α的转变主要涉及链构象的轻微重排(特别是与侧基有关的)和晶胞内的堆积方式向能量更有利的状态转变，对应于晶胞尺寸的减小。此外，还提出了α‘-α转变主要是通过直接固-固转变机制进行的。此外，还发现分子量对结晶相变有显著的影响。在低相对分子质量的PLLA样品中，α‘到α的转变变得更快，即使在相对较低的温度下也可以显著地进行。
Effects of annealing conditions and molecular weight (MW) on the crystalline phase transition in Poly(L-lactide) (PLLA) were studied by wide-angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). The disordered crystal (alpha'-form) of PLLA was found to transform into the alpha one during annealing process at elevated temperatures. The alpha'-to-alpha transition is quite dependent on the annealing period (t(a): 0-1440 min) and annealing temperature (T-a: 120-160 degrees C). With increasing T-a, the polymorphic transition progresses much more rapidly. The alpha'-to-alpha transition is mainly involved by the slight rearrangement of the chain conformation (especially related to the side groups) and packing manner in the unit cell to the more energy-favorable state, corresponding to the reduction of unit cell dimension. Besides, it was proposed that the alpha'-to-alpha transformation mainly proceeds by the direct solid-solid transition mechanism. Moreover, it was found that MW affects the crystalline phase transition significantly. In the low-MW PLLA sample, the alpha'-to-alpha transition becomes much faster, and it can proceed prominently even when annealed at relatively lower temperature.