Stereocomplexes of Discrete, Isotactic Lactic Acid Oligomers Conjugated with Oligodimethylsiloxanes
Stereocomplexes of Discrete, Isotactic Lactic Acid Oligomers Conjugated with Oligodimethylsiloxanes
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DOI：
10.1021/acs.macromol.8b02529
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发表时间：
2019-02-12
期刊：
影响因子：
5.5
通讯作者：
Meijer, E. W.
中科院分区：
文献类型：
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作者：
Lamers, Brigitte A. G.;van Genabeek, Bas;Meijer, E. W.
离散长度块体共低聚物（BCOs）是由晶体和非晶态块体组成的一类新型材料，在小长度尺度上具有高度有序的层状结构。在这里，我们展示了离散的、等规的低聚L-和d -乳酸（oLLA和oDLA）同源块的制备，然后连接到低聚二甲基硅氧烷（oDMS），提供了一个分子量和组成不同的结晶-无定形BCOs库。混合这两种对映体BCOs或同位块会形成相应的立体配合物。用差示扫描量热法和小角x射线散射研究了等规（嵌段co）低聚物及其立体配合物的性质和相行为。对等规同嵌段长度和晶体结构的系统研究证实，立体配合物形成了10(3)螺旋，单体上升0.3 nm，而立体配合物采用3(1)螺旋。同样的晶体结构也存在于BCOs的等规和立体配合物中，它们在室温下由于oLA块的结晶而形成片层状结构。在BCOs中发现扭曲的片层结构，在结晶之前预先组织成非片层形态。由于晶化驱动力较大，立体配合物BCOs在微观结构中存在较多的晶体缺陷和长程有序缺失。因此，链长、块体积和结晶强度之间的平衡对于形成缺陷最少的最终结构至关重要。
Discrete length block co-oligomers (BCOs) comprised of a crystalline and an amorphous block are a new class of materials that gives highly ordered lamellar morphologies at small length scales. Here, we show the preparation of discrete, isotactic oligo L- and D-lactic acid (oLLA and oDLA) homoblocks followed by ligation to oligodimethylsiloxane (oDMS), affording a library of crystalline-amorphous BCOs that vary in molecular weight and composition. Mixing the two enantiomeric BCOs or homoblocks results in the formation of the corresponding stereocomplex. The properties and phase behavior of the isotactic (block co)oligomers and the stereocomplexes thereof are studied using differential scanning calorimetry and small-angle X-ray scattering. A systematic study of the isotactic homoblock lengths and crystal structure confirmed the formation of a 10(3) helix with a monomeric rise of 0.3 nm, whereas the stereocomplex adopts a 3(1) helix. The same type of crystal structure was found for the isotactic and stereocomplex of BCOs giving rise to the formation of lamellar morphologies at room temperature as a result of crystallization of the oLA blocks. Distorted lamellar structures were found in BCOs that preorganize into nonlamellar morphologies prior to crystallization. The stereocomplex BCOs shows more crystal defects and a loss of long-range ordering in the microstructure due to the larger driving force for crystallization. Hence, the balance between chain length, block volume, and the crystallization strength are of major importance for the formation of the final structure with the least defects.