An Applicability Study on Various Methods for Determining the Monomer Conversion Rate of Polyamide 6

Anionic ring opening polymerization of epsilon-caprolactam (CL) results in the formation of high molecular weight polyamide 6 (PA6) within a few minutes. The monomer conversion rate is an important characterization parameter for polymerization process as well as the end products. This paper used PA6 films with different polymerization degrees as research object for the first time, and systematically compared the performance of four methods for measuring CL conversion rate. The analytical methods were solvent extraction (methanol, ethanol, or water), vacuum removal, thermogravimetric analysis (TGA), and absorbance ratio respectively. For all PA6 products, solvent extraction based on methanol/water and vacuum removal were effective methods for determine their conversion rates. And TGA was only applicable for samples with high degree of polymerization. The CL conversion rate obtained by solvent extraction based on ethanol and absorbance ratio was slightly higher than the real value, especially the latter. Moreover, a new method was discovered and validated during the research process, namely atmospheric devolatilization. The methodology and results in this study can be employed for guiding the production and application of polymers, especially the reactive processing of PA6. Applicability evaluation of various methods for determining monomer conversion rate of PA6 products prepared by anionic polymerization. image