Bates Morgan W, Barbon Stephanie M, Levi Adam E, Lewis Ronald M, Beech Haley K, Vonk Kasper M, Zhang Cheng, Fredrickson Glenn H, Hawker Craig J, Bates Christopher M
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States.
ACS Macro Lett. 2020 Mar 17;9(3):396-403. doi: 10.1021/acsmacrolett.0c00061. Epub 2020 Feb 27.
The stability of tetrahedrally close-packed (TCP) phases in block copolymer melts is predicted by theory to depend on molecular architecture, yet no experimental studies to date have probed its effect. Motivated by this open question, here we report an efficient synthesis of asymmetric AB miktoarm star polymers using functionalized sugars as cores for orthogonal grafting-from block copolymerizations. A combination of ring-opening and atom transfer radical polymerization produced model low dispersity materials comprising a single A = poly(lactide) (L) and multiple B = poly(dodecyl acrylate) (D) arms that amplify "conformational asymmetry" through two concerted effects: the mikto architecture and disparate block statistical segment lengths. Analyzing the self-assembly of LD and LD samples resulted in the discovery of two TCP phases, σ and A15, that remained stable to significantly higher A-block volume fractions as the number of B arms increased. These results experimentally establish the importance of conformational asymmetry and molecular architecture as powerful design tools for the self-assembly of block copolymers into nonclassical phases.
理论预测，嵌段共聚物熔体中四面体密堆积（TCP）相的稳定性取决于分子结构，但迄今为止尚无实验研究探究其影响。受这个悬而未决的问题的启发，我们在此报告了一种高效合成不对称AB型米克托臂星型聚合物的方法，该方法使用功能化糖作为核，用于正交接枝-从嵌段共聚反应。开环聚合和原子转移自由基聚合相结合，制备了具有低分散性的模型材料，该材料由单个A =聚丙交酯（L）和多个B =聚十二烷基丙烯酸酯（D）臂组成，通过两种协同效应放大了“构象不对称性”：米克托结构和不同的嵌段统计链段长度。分析LD和LD样品的自组装过程，发现了两个TCP相，即σ相和A15相，随着B臂数量的增加，这两个相在显著更高的A嵌段体积分数下仍保持稳定。这些结果通过实验证明了构象不对称性和分子结构作为强大的设计工具，对于将嵌段共聚物自组装成非经典相的重要性。
