State Key Laboratory of Fine Chemicals , Dalian University of Technology , Dalian 116024 , China.
Department of Chemistry and Chemical Biology, Baker Laboratory , Cornell University , Ithaca , New York 14853-1301 , United States.
J Am Chem Soc. 2019 Sep 18;141(37):14780-14787. doi: 10.1021/jacs.9b07058. Epub 2019 Sep 10.
We report a comprehensive understanding of the stereoselective interaction between two opposite enantiomeric polyesters prepared from the regioselective copolymerization of chiral terminal epoxides and cyclic anhydrides. For many of the resultant polyesters, the interactions between polymer chains of opposite chirality are stronger than those of polymer chains with the same chirality, resulting in the formation of a stereocomplex with an enhanced melting point () and crystallinity. The backbone, tacticity, steric hindrance of the pendant group, and molecular weight of the polyesters have significant effects on stereocomplex formation. Bulky substituent groups favor stereocomplexation, resulting in a greater rise in in comparison to the component enantiomeric polymers. The stereocomplex assembly of discrete ()- and ()-poly(phenyl glycidyl ether--phthalic anhydride)s oligomers revealed that the minimum degree of polymerization required for stereocomplex formation is five. Raman spectroscopy and solid-state NMR studies indicate that stereocomplex formation significantly restricts the local mobilities of C═O and C-H groups along the backbone of chains. The reduced mobility results in the enhanced spin-lattice relaxation time and both H and C downfield shifts due to the strong intermolecular interactions between - and -chains.
我们全面了解了两种对映异构聚酯之间的立体选择性相互作用，这两种聚酯是通过手性末端环氧化物和环状酸酐的区域选择性共聚制备的。对于许多得到的聚酯，具有相反手性的聚合物链之间的相互作用强于具有相同手性的聚合物链之间的相互作用，导致形成熔点（）和结晶度提高的立体复合物。聚酯的主链、立构规整性、侧基的空间位阻和分子量对立体复合物的形成有显著影响。大体积取代基有利于立体络合，与组成对映异构聚合物相比，在中观察到更大的上升。离散的（）-和（）-聚（苯缩水甘油醚-邻苯二甲酸酐）低聚物的立体复合物组装表明，形成立体复合物所需的最低聚合度为五。拉曼光谱和固态 NMR 研究表明，立体复合物的形成显著限制了链主链上 C═O 和 C-H 基团的局部迁移率。由于 -和 -链之间的强分子间相互作用，迁移率的降低导致自旋晶格弛豫时间延长和 H 和 C 向低场位移。
