Suspension polymerization of 2‐pyrrolidone in the presence of CO2 and organic promoters

Polybutyrolactam (PBL), known as polyamide 4 with high performance, was synthesized using CO2 by combining organic promoters in suspension to overcome the limitations of traditional bulk polymerization and improve the thermal stability. Upon increasing the amount of paraffin oil or sodium dodecyl sulfate, which proved to be the most suitable medium and dispersant, or increasing the concentration of alkaline catalyst and CO2, or the rate of stirring, the inherent viscosity increased first and then decreased, while the yield did not follow the same trend. Adding 18‐crown‐6 ether greatly increased the yield but decreased the inherent viscosity, contrary to the trend that was reported for bulk polymerization. The yield and inherent viscosity both increased with increasing concentration of tetramethyl ammonium chloride. PBL particles were loosely structured and presented improved thermal stability compared with any other report on suspension polymerization. This study provides a promising method to produce PBL with high performance on a large scale. Suspension polymerization of 2‐pyrrolidone in the presence of CO2 and organic promoters. Combining CO2 and organic promoters in suspension polymerization, loosely structural particles of polybutyrolactam, also known as polyamide 4, is synthesized. Compared with those using acyl chloride initiators in suspension polymerization, the thermal stability and the molecular weight of the products are improved. It provides a promising way to product polybutyrolactam on large scale with low cost and high performance.