Double-stranded helical polymers consisting of complementary homopolymers

Area of Science:

• Supramolecular Chemistry
• Polymer Science
• Organic Synthesis

Background:

• Development of self-assembling polymeric systems is crucial for advanced materials.
• Chiral recognition and helical structures are fundamental in biological and synthetic systems.
• Amidinium-carboxylate interactions offer a route to directed self-assembly.

Purpose of the Study:

• To synthesize complementary homopolymers with m-terphenyl-based backbones.
• To investigate the self-assembly behavior of these polymers into double helical structures.
• To explore the influence of solvent polarity and chemical treatment on the resulting supramolecular architecture.

Main Methods:

• Sonogashira cross-coupling reaction for the synthesis of diethynyl monomers and subsequent copolymerization.
• Spectroscopic techniques (UV-Vis absorption, circular dichroism, IR) to characterize the assembled structures.
• Atomic force microscopy (AFM) for high-resolution imaging and determination of helical sense.

Main Results:

• Successful synthesis of two complementary homopolymers containing chiral amidine and achiral carboxylic acid groups.
• Formation of a preferred-handed double helix in THF via interstrand amidinium-carboxylate salt bridges.
• Kinetic formation of an imperfect double helical interpolymer complex in chloroform, which can be rearranged into a perfect double helix upon acid-base treatment.

Conclusions:

• Complementary polymers can self-assemble into well-defined double helical structures driven by specific non-covalent interactions.
• Solvent polarity plays a critical role in controlling the kinetics and thermodynamics of polymer self-assembly.
• The study demonstrates a method for correcting kinetically trapped supramolecular structures, offering control over helical architecture.