Duan Yongxin, Liu Jing, Sato Harumi, Zhang Jianming, Tsuji Hideto, Ozaki Yukihiro, Yan Shouke
State Key Laboratory of Polymer Physics & Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People's Republic of China.
Biomacromolecules. 2006 Oct;7(10):2728-35. doi: 10.1021/bm060043t.
The molecular weight dependence of poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) stereocomplex behavior at the air-water interface was studied by surface pressure-area (pi-A) isotherms and atomic force microscopy (AFM). It was found that the compression-induced sterecomplexation of a PDLA/PLLA equimolar blend with high molecular weight (M(w) = 1 x 10(6) and 9.8 x 10(5), respectively) could occur at the air-water interface. This result is in marked contrast with the stereocomplexation of PDLA/PLLA blends in the bulk from the melt or in solutions, where the homocrystallites of either PLLA or PDLA rather than stereocomplex crystallites will be formed preferentially when the molecular weights of both polymers are higher than 1 x 10(5). Unexpectedly, the Langmuir-Blodgett behavior of the PDLA/PLLA blend with lower molecular weight (M(w) = 4 x 10(3) and 3.2 x 10(3), respectively), which should be favored in the stereocomplex, was distinct from that of other higher molecular weight blends. AFM images clearly disclosed for the first time the morphological changes of the equimolar blends of PLLA and PDLA at the air-water interface induced by increasing the surface pressure of the monolayer. Of particular note, the bilayer mechanism for the plateau in the isotherm was directly verified by the AFM height images.
通过表面压力-面积（π-A）等温线和原子力显微镜（AFM）研究了聚（L-丙交酯）/聚（D-丙交酯）（PLLA/PDLA）立体络合物在气-水界面的行为与分子量的关系。结果发现，高分子量（Mw分别为1×10⁶和9.8×10⁵）的PDLA/PLLA等摩尔共混物在气-水界面可发生压缩诱导的立体络合。这一结果与PDLA/PLLA共混物在本体中从熔体或溶液中的立体络合形成明显不同，在本体中，当两种聚合物的分子量均高于1×10⁵时，优先形成的是PLLA或PDLA的均聚物晶体而非立体络合物晶体。出乎意料的是，较低分子量（Mw分别为4×10³和3.2×10³）的PDLA/PLLA共混物（在立体络合中本应更有利）的Langmuir-Blodgett行为与其他较高分子量共混物不同。AFM图像首次清晰地揭示了随着单层表面压力增加，PLLA和PDLA等摩尔共混物在气-水界面的形态变化。特别值得注意的是，等温线平台的双层机制通过AFM高度图像得到了直接验证。
