Pathway Complexity in Supramolecular Copolymerization and Blocky Star Copolymers by a Hetero-Seeding Effect

Area of Science:

• Supramolecular Chemistry
• Polymer Science
• Materials Science
• Chiral Self-Assembly

Background:

• Chiral dipolar naphthalene monoimide (NMI) building blocks, O-NMI and S-NMI, differ by a single heteroatom (oxygen vs. sulfur).
• Understanding their distinct self-assembly behaviors is crucial for designing novel supramolecular materials.
• Competing interactions, including dipolar forces and hydrogen bonding, govern the assembly of NMI derivatives.

Purpose of the Study:

• To elucidate the kinetic and thermodynamic pathways governing the supramolecular copolymerization of O-NMI and S-NMI.
• To investigate the influence of heteroatom substitution on self-assembly complexity, hierarchical organization, and chiroptical properties.
• To explore the formation of different supramolecular architectures, including statistical and block copolymers, and star-shaped structures.

Main Methods:

• Investigation of self-assembly pathways through analysis of competing dipolar interactions and amide-amide hydrogen bonding.
• Exploration of thermodynamic routes via equimolar monomer mixtures leading to statistical supramolecular copolymers.
• Examination of kinetic routes involving sequence-controlled monomer addition for hetero-seeded block copolymerization and star copolymer formation.

Main Results:

• O-NMI exhibits complex self-assembly into nanotapes and helical fibers via antiparallel and parallel stacking, respectively, unlike S-NMI's stable spherical assembly due to stronger H-bonding.
• Thermodynamic copolymerization yields chiral statistical copolymers, while kinetic control enables hetero-seeded block copolymerization.
• A core-multiarmed 'star' copolymer is formed by nucleating O-NMI onto S-NMI seeds, with controllable arm length; helical bias in O-NMI is inhibited in the star topology due to S-NMI seed's lack of stereoregularity.

Conclusions:

• The heteroatom difference between O-NMI and S-NMI significantly dictates their supramolecular polymerization behavior and resulting architectures.
• Precise control over kinetic and thermodynamic pathways allows for the rational design of complex chiral supramolecular copolymers.
• The study demonstrates a novel method for creating star-shaped copolymers with tunable properties and highlights the impact of seed stereoregularity on helical assembly.