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Differences Between Two PEEK Synthesis Routes

Overview of Technical Route Differences

1. Nucleophilic Substitution Route (Mainstream Method)
   Most mainstream companies use the nucleophilic substitution method. Patent innovation from various companies usually focuses on condensing agents.

• Victrex (UK) first successfully developed PEEK synthesis in the 1970s.

• Industrial-scale production started in 1987 using a method involving fluoroketone and hydroquinone.

• Most Chinese companies also adopt this method.

2. Electrophilic Substitution Route (Less Common)

• Solvay acquired India’s Gharda, which once filed a patent based on the electrophilic route.

• It is unclear whether Solvay's current production uses this method.

• According to a thesis from Fudan University (Ren Wenqing), industrialized PEEK synthesis mainly follows the nucleophilic route.

Patents Related to Electrophilic Route

1. European Patent EP0174207

• Describes the synthesis of PEEK via Friedel-Crafts acylation reactions.

2. US Patent US 6881816 (Gharda’s Patent)

• Uses Phenoxyphenoxybenzoic acid (PPBA) as the monomer.

• The reaction occurs in methanesulfonic acid (MSA) with condensing agents like MSA anhydride, phosphorus pentoxide (P₂O₅), or thionyl chloride (SOCl₂).

• The carboxylic acid reacts with the para-position of the phenyl ether to form a ketone bond while releasing water.

Summary of Performance Differences

Products synthesized via electrophilic and nucleophilic substitution differ in reaction mechanisms and final properties.

• Nucleophilic Substitution Route

• Higher molecular weight

• Narrower molecular weight distribution

• Electrophilic Substitution Route

• Lower molecular weight

• Broader molecular weight distribution

Reaction Mechanisms

Nucleophilic Substitution Route

• Reactants: Fluorinated monomers and base catalysts (Na₂CO₃, K₂CO₃, SrCO₃)

• Mechanism: SNAr (nucleophilic aromatic substitution)

• Result: Higher-quality PEEK with a molecular weight >50,000 Da and PDI (Polydispersity Index) between 1.2–1.5

Electrophilic Substitution Route

• Reactants: Acyl chlorides, catalysts like AlCl₃

• Mechanism: Friedel–Crafts acylation

• Result: PEEK with lower molecular weight (<20,000 Da) and PDI >2.5

Comparative Summary (4 Main Aspects)

1. Reaction Type

• Nucleophilic: Base catalysis, SNAr mechanism

• Electrophilic: Acid catalysis, Friedel–Crafts mechanism

2. Reagents and Catalysts

• Nucleophilic: K₂CO₃/Na₂CO₃, monomers with fluoride groups

• Electrophilic: AlCl₃, PPBA-COCl

3. Molecular Characteristics

• Nucleophilic: Mw = 30,000–80,000, PDI = 1.3–2

• Electrophilic: Mw ≈ 15,000, PDI >3

4. Purity and Conversion Efficiency

• Nucleophilic: High purity (>95%), consistent conversion

• Electrophilic: Lower purity, limited commercial application

Conclusion

Although the electrophilic route has theoretical and academic interest, the nucleophilic substitution method remains the dominant industrial synthesis route for PEEK due to its higher molecular weight and consistent performance characteristics.