Topochemical Photopolymerization above the Bulk Melting Temperature in Noncovalent Monolayers on Graphite

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Chemistry

Background:

• Surface-templated reactions are crucial for materials synthesis.
• Monomer ordering is often emphasized, but Ångström-scale dynamics are vital for bond formation.
• 10,12-tricosadiynoic acid (TCDA) is a common diacetylene monomer used in such reactions.

Purpose of the Study:

• To investigate the effect of elevated temperatures on the topochemical reaction efficiency of TCDA on highly oriented pyrolytic graphite (HOPG).
• To understand the relationship between temperature, reaction dynamics, and polymer properties.
• To assess the impact on subsequent covalent mesh-forming reactions.

Main Methods:

• Assembling TCDA monomers on HOPG substrates.
• Conducting topochemical polymerization at various temperatures (5°C to 65°C).
• Analyzing reaction kinetics, degree of polymerization, and polymer density using spectroscopic and microscopic techniques.

Main Results:

• Arrhenius temperature dependence observed up to ≈45°C with an activation energy (Ea) of 5.9 kcal mol⁻¹ (0.26 eV).
• At higher temperatures, the degree of polymerization increased significantly (from 97 at 5°C to 248 at 65°C).
• Polymer density increased 6-13 fold at elevated temperatures, enhancing molecular sheet integrity and covalent mesh formation efficiency by 10-fold.

Conclusions:

• Elevated temperatures beyond ≈45°C do not follow simple Arrhenius behavior but significantly enhance TCDA polymerization efficiency on HOPG.
• Increased monomer dynamics at higher temperatures lead to higher molecular weight polymers and improved sheet integrity.
• This temperature-controlled enhancement is critical for efficient transfer of TCDA sheets in covalent mesh-forming reactions.