Insights into the Molecular Dynamics in Polysulfone Polymers from (13)C Solid-State NMR Experiments

Area of Science:

• Polymer Science
• Solid-State Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science

Background:

• Polysulfones (PESU, PSU, PPSU) are high-performance engineering thermoplastics.
• Understanding their molecular dynamics is crucial for predicting material properties and performance.
• Ductile polysulfones exhibit complex behaviors influenced by molecular motion.

Purpose of the Study:

• To investigate the molecular and segmental motions in three distinct grades of ductile polysulfone polymers.
• To characterize the dynamics of phenyl rings and segmental chains using advanced NMR techniques.
• To elucidate the nature of mobile regions within these polymer structures.

Main Methods:

• Utilized (13)C solid-state NMR experiments.
• Employed Polarization Inversion Spin Exchange at Magic Angle (PISEMA) to probe fast motions.
• Applied Center Band Only Detection of Exchange (CODEX) to assess slow segmental motions.
• Conducted temperature-dependent PISEMA and (13)C spin-lattice relaxation time (T1) experiments.

Main Results:

• PISEMA experiments revealed π-flip motions of phenyl rings occurring at approximately 100 kHz.
• Temperature-dependent studies showed a greater fraction of mobile regions undergoing aromatic π-flips in poly(phenyl sulfone) (PPSU) compared to PESU and PSU.
• CODEX experiments did not detect any slow segmental motions within the polymer chains.
• (13)C spin-lattice relaxation time (T1) and T1-filtered PISEMA experiments indicated dynamic heterogeneity in the mobile regions of all tested polymers.

Conclusions:

• Polysulfone polymers exhibit fast aromatic π-flip motions.
• Poly(phenyl sulfone) (PPSU) demonstrates higher mobility in its aromatic regions than PESU and PSU.
• The mobile regions within these ductile polysulfones are characterized by dynamic heterogeneity, suggesting varied local environments.