Mechanochemistry in Block Copolymers: New Scission Site due to Dynamic Phase Separation

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Mechanochemistry can degrade covalent macromolecules, affecting material properties.
• Block copolymers (BCPs) are crucial functional materials, but susceptible to mechanochemical damage during processing.
• Understanding BCP mechanochemistry is vital for material performance and longevity.

Purpose of the Study:

• To investigate the mechanochemical response of block copolymers (BCPs) in solution.
• To determine the influence of monomer ratio on BCP mechanochemistry.
• To elucidate the molecular mechanisms behind BCP chain scission.

Main Methods:

• Synthesis of BCPs with varying butyl acrylate and methyl methacrylate ratios.
• Solution-phase mechanochemical stress via ultrasonication.
• Analysis using size-exclusion chromatography and molecular dynamics modeling.

Main Results:

• BCPs showed mechanochemistry rate constants similar to methacrylate homopolymers, irrespective of composition.
• A secondary scission site was identified at the covalent junction between blocks.
• Molecular dynamics revealed dynamic phase separation in BCPs, even in good solvents.
• Chain overstretching models support non-center-chain bond scission.

Conclusions:

• BCP mechanochemistry is influenced by inherent chain conformations and dynamic phase separation.
• The block junction acts as a preferential site for mechanochemical scission.
• Findings suggest that polymer processing conditions need careful consideration for BCPs.