Double Crystallization and Phase Separation in Polyethylene-Syndiotactic Polypropylene Di-Block Copolymers

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Semicrystalline block copolymers (BCPs) exhibit complex morphologies due to competing crystallization and phase separation.
• In crystalline-BCPs, the sequence of block crystallization significantly influences the final solid-state structure.
• Controlling BCP morphology is crucial for developing advanced materials with tailored properties.

Purpose of the Study:

• To investigate the use of epitaxial crystallization on crystalline substrates to control the morphology of crystalline-crystalline block copolymers.
• To determine the influence of substrate choice on the crystallization sequence and resulting nanostructure of polyethylene-block-syndiotactic polypropylene (PE-b-sPP).
• To demonstrate a method for producing highly oriented nanostructures in BCPs.

Main Methods:

• Synthesis of polyethylene-block-syndiotactic polypropylene (PE-b-sPP) using a stereoselective living organometallic catalyst.
• Epitaxial crystallization of PE-b-sPP onto two distinct crystalline substrates: p-terphenyl (3Ph) and benzoic acid (BA).
• Analysis of the resulting highly ordered morphologies using techniques to determine crystal orientation and crystallization sequence.

Main Results:

• Epitaxial crystallization on both 3Ph and BA substrates induced highly oriented crystalline lamellae of both PE and sPP blocks.
• The substrate determined the crystallization sequence: sPP crystallized first on 3Ph, and PE crystallized first on BA.
• Observed single orientations of both crystalline phases on both substrates, indicating a dominant role of the first-crystallizing block in defining the overall morphology.
• This allowed discrimination between crystalline phases and control over final morphology based on substrate interaction.

Conclusions:

• Epitaxial crystallization on selected substrates provides precise control over block copolymer morphology by dictating the crystallization sequence.
• The choice of substrate is critical in determining which polymer block crystallizes first, thereby controlling the final nanostructure.
• This approach offers a versatile strategy for fabricating oriented nanostructures in block copolymers for various applications.