Facile Synthesis and Enhanced Aggregation-Induced Circular Dichroism of Novel Chiral Polyamides

Abstract

A series of optically active polyamides, PAnLATs (n = 9-12), were prepared by polycondensation of l-tartrate-derived diacid with achiral aliphatic diamines in which the number of the methylene is from 9 to 12. The monomers could be obtained easily, and the synthesis of the polyamides is facile. The number-average molecular weight (Mn) of PA9LAT, PA10LAT, PA11LAT, and PA12LAT is 35 500, 24 400, 35 800, and 20 900 g/mol, respectively, and the related polydispersity index is 3.4, 3.3, 3.4, and 3.0. These polyamides display intense optical activity in solution. Particularly, the stronger ellipticities and different circular dichroism (CD) images were presented when the polymers were evaluated in the solid state. The crystalline properties of the polymers were studied to illuminate the enhanced aggregation-induced CD. Moreover, PA9LAT and PA11LAT have similar crystal parameters, and PA10LAT is similar to PA12LAT, which revealed why the chirality of the polyamides displays an odd-even effect. On the other hand, the solubility of the polymers in organic solvents was studied, and thermogravimetric-differential thermal analyzer was utilized to characterize the thermal properties.