Post-Polymerization Modification to Synthesize Atactic and Isotactic Polyacrylonitrile Copolymers and Related Carbon...

Area of Science:

• Polymer Chemistry
• Materials Science
• Nanotechnology

Background:

• Polyacrylonitrile (PAN) is the primary precursor for over 90% of carbon fibers (CFs).
• Conventional PAN synthesis lacks stereochemical control, resulting in broad dispersity and impacting CF properties.
• The stereochemistry of the PAN precursor is crucial for the graphitization and final properties of CFs.

Purpose of the Study:

• To develop a novel method for synthesizing isotactic PAN (iPAN) with controlled stereochemistry.
• To investigate the effect of iPAN precursor stereochemistry on the properties of derived carbon fibers.
• To improve the tensile strength and modulus of PAN-based carbon fibers.

Main Methods:

• A two-step process involving Lewis acid-catalyzed stereocontrolled polymerization of tert-butylacrylamide to form isotactic PTBAM (iPTBAM).
• Post-polymerization modification to convert iPTBAM into isotactic polyacrylonitrile (iPAN-TB).
• Wet spinning of iPAN-TB and control PAN into precursor fibers, followed by high-temperature processing (250 °C and 1500 °C).

Main Results:

• Synthesized iPTBAM with low dispersity (<1.25) and high isotacticity (approx. 77% mm triads).
• Achieved up to 78% conversion of acrylamide groups to nitriles in iPAN-TB.
• iPAN-TB derived carbon fibers showed a nearly six-fold increase in tensile strength and a four-fold increase in modulus compared to control PAN fibers after heating, without compromising extensibility.

Conclusions:

• Stereocontrolled synthesis of iPAN provides a pathway to advanced carbon fibers.
• The enhanced mechanical properties of iPAN-based CFs are attributed to improved precursor stereochemistry.
• This approach offers a significant advancement in PAN-based carbon fiber technology.