Preparation and Performance Study of Carboxylated Nitrile Rubber Based on Phase Transfer Catalysis: Screening of Optimal Catalyst System.

This study systematically screened twelve phase transfer catalysts from three categories, namely ammonium-based compounds, phosphonium-based compounds, and polyethylene glycols of different molecular weights, for the preparation of carboxylated nitrile rubber (XNBR) via phase transfer catalytic hydrolysis. The carboxyl content of the resulting XNBR was quantitatively determined by titration, revealing significant variations with catalyst structure ranging from 0 to 2.2 wt%. Phosphonium catalysts exhibited the highest carboxylation efficiency, with TBPB achieving 2.2 wt%, while ammonium catalysts showed structure-dependent performance, with TBAB reaching 1.1 wt%. PEG catalysts demonstrated optimal efficiency at intermediate molecular weights, with PEG-300 achieving 0.8 wt% and PEG-600 achieving 0.6 wt% but suffered from residual contamination. Through comprehensive evaluation of catalytic efficiency, reaction controllability, safety, and product purity, tetrabutylammonium bromide (TBAB) was identified as the optimal catalyst, achieving the best balance between carboxyl content (1.1 wt%), mild reaction kinetics, minimal catalyst residue, and product uniformity. Using TBAB as the catalyst, XNBR with low (1.1%) and high (3.1%) carboxyl contents were successfully prepared by controlling reaction time. The research demonstrated that carboxyl content had a decisive impact on vulcanization characteristics, mechanical properties, and thermal stability of XNBR. As carboxyl content increased, crosslink density significantly increased, leading to marked improvement in tensile stress at given elongation, tensile strength, and hardness, while elongation at break showed a decreasing trend. Thermogravimetric analysis demonstrated that carboxyl group introduction effectively enhanced the thermal stability of the material. This study provides an important theoretical basis and practical guidance for regulating the carboxylation degree through catalyst molecular design and preparing XNBR with excellent comprehensive performance.