Single-crystal-to-single-crystal topochemical polymerizations by design

Area of Science:

• Materials Science
• Polymer Chemistry
• Supramolecular Chemistry

Background:

• Conjugated polymers like polydienes are industrially significant, but polymers from diacetylenes, trienes, and triacetylenes are rare.
• Traditional topochemical polymerization of diacetylenes is unreliable, requiring specific pre-organized monomer structures for successful solid-state reactions.
• Most diacetylene monomers lack the necessary solid-state arrangement for polymerization, limiting the synthesis of novel conjugated materials.

Purpose of the Study:

• To develop a versatile supramolecular host-guest strategy for synthesizing new conjugated polymers from diacetylenes, triacetylenes, and trienes.
• To overcome the limitations of existing polymerization methods by imposing required structural parameters on monomers.
• To explore the synthesis of previously inaccessible polymer structures, including terminal polydiacetylenes and polytriacetylenes.

Main Methods:

• Utilized a supramolecular host-guest approach, employing self-assembled host molecules (e.g., oxalamides, vinylogous amides) to control monomer spacing.
• Designed hosts with specific substituents to bind guest monomers (diacetylenes, triacetylenes) via hydrogen or halogen bonding, achieving ideal intermolecular distances (e.g., 4.9 Å for diacetylenes, 7.4 Å for triacetylenes).
• Performed single-crystal-to-single-crystal polymerizations to enable characterization of polymers in crystalline form and study reaction pathways.

Main Results:

• Successfully synthesized new classes of polydiacetylenes, including the first terminal polydiacetylenes and an aryl-substituted diacetylene.
• Prepared poly(diiododiacetylene), the simplest known polydiacetylene, using halogen bonding for host-guest interaction.
• Synthesized polytriacetylenes by designing pyridine-substituted vinylogous amide hosts to achieve the required 7.4 Å spacing for triacetylene polymerization.

Conclusions:

• The supramolecular host-guest strategy is a powerful and adaptable method for synthesizing challenging conjugated polymers.
• This approach enables precise control over monomer arrangement, overcoming limitations of traditional polymerization techniques.
• The synthesized polymers, including novel polydiacetylenes and polytriacetylenes, offer new platforms for exploring structure-property relationships in conjugated materials.