Unique toroidal morphology from composition and sequence control of triblock copolymers

Area of Science:

• Polymer Science
• Materials Science
• Supramolecular Chemistry

Background:

• Triblock copolymers self-assemble into complex morphologies.
• Understanding the factors governing self-assembly is key for materials design.

Purpose of the Study:

• To investigate the mechanism of toroidal supramolecular assembly formation in acrylic acid, methyl acrylate, and styrene triblock copolymers.
• To determine the influence of block copolymer composition and sequence on self-assembly.

Main Methods:

• Synthesis and characterization of four block copolymers: PAA99-b-PMA73-b-PS66, PAA99-b-PS76-b-PMA62, PAA99-b-PMA155, and PAA99-b-PS133.
• Solution-state self-assembly studies in varying tetrahydrofuran/water compositions with 2,2'-(ethylenedioxy)bis(ethylamine).
• Morphology determination using transmission electron microscopy.

Main Results:

• Toroidal supramolecular assemblies were formed by PAA99-b-PMA73-b-PS66.
• Diblock copolymers with comparable hydrophobic segments (PMA or PS) did not form toroidal structures.
• A triblock copolymer with a reversed sequence of hydrophobic blocks (PAA99-b-PS76-b-PMA62) also failed to form toroidal assemblies.

Conclusions:

• The specific sequence of acrylic acid, methyl acrylate, and styrene blocks is critical for the formation of unique toroidal supramolecular assemblies.
• Block copolymer sequence plays a more significant role than the total length of hydrophobic segments in dictating self-assembly outcomes.