Mechanistic insights for block copolymer morphologies: how do worms form vesicles?

Area of Science:

• Polymer Chemistry
• Materials Science
• Nanotechnology

Background:

• Amphiphilic diblock copolymers mimic cell membranes but typically self-assemble only in dilute solutions (<1%).
• This dilution limits their commercial applications in areas like drug delivery and coatings.
• Polymerization-induced self-assembly offers a potential solution to overcome these limitations.

Purpose of the Study:

• To develop a one-pot, in situ method for synthesizing and self-assembling amphiphilic AB diblock copolymers in concentrated aqueous dispersions.
• To achieve predictable formation of various nanostructures (spheres, worms, vesicles) at high solids content.
• To investigate the mechanistic pathways of nanostructure formation during polymerization.

Main Methods:

• Synthesis of amphiphilic AB diblock copolymers via aqueous dispersion polymerization.
• In situ monitoring of polymerization and self-assembly using transmission electron microscopy (TEM).
• Characterization of nanostructure morphology at high solids concentration.

Main Results:

• Predictable and efficient formation of spherical micelles, wormlike micelles, and vesicles within 2 hours and >99% monomer conversion.
• Observation of novel intermediate structures (e.g., branched worms, "octopi", "jellyfish") providing mechanistic insights.
• Successful self-assembly achieved at high solids (>1%) in purely aqueous solution without toxic solvents.

Conclusions:

• A novel, environmentally benign, and scalable one-pot polymerization method enables concentrated self-assembly of block copolymers into defined nanostructures.
• The method overcomes the dilution limitation of conventional self-assembly, paving the way for industrial applications.
• In situ TEM observations provide crucial understanding of the dynamic morphological evolution during copolymer self-assembly.