Computational mechanistic studies on persulfate assisted p-phenylenediamine polymerization

Area of Science:

• Polymer Chemistry
• Computational Chemistry
• Materials Science

Background:

• p-Phenylenediamine (p-PDA) is a key monomer for high-performance polymers like Kevlar.
• The free-radical polymerization mechanisms of aromatic diamines are not fully understood computationally.
• Potassium persulfate (K2S2O8) is a common initiator for such polymerizations.

Purpose of the Study:

• To elucidate the role of potassium persulfate (K2S2O8) in the free-radical polymerization of p-PDA.
• To computationally investigate the reaction mechanism and energy barriers involved.
• To support experimental protocols and expand the scope of polymer applications.

Main Methods:

• Density Functional Theory (DFT) with the B3LYP-D3 functional was employed.
• Calculations were performed under experimental conditions (0°C, aqueous media).
• The roles of sulfate free-radical (SFR), persulfate anion (PA), and K2S2O8 cluster (PP) were analyzed.

Main Results:

• The dimerization step is the rate-limiting step when initiated by SFR (29.2 kcal/mol).
• PA-assisted dimerization significantly lowers the energy barrier to 12.7 kcal/mol.
• PP-supported polymerization exhibits very low energy barriers for dimerization (11.6 kcal/mol) and ammonia extrusion (6.7 kcal/mol).

Conclusions:

• Potassium persulfate's initiation mechanism is highly dependent on the specific species involved (SFR, PA, PP).
• PA and PP offer more efficient pathways for p-PDA polymerization compared to SFR.
• Computational insights provide a foundation for optimizing experimental polymerization conditions and polymer design.