The solid-state polymerization (SSP) of PA66 is a critical method for adjusting the macromolecular weight and mechanical properties. In this study

one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy (NMR)

and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were utilized to analyze the chemical structure of by-products in PA66 pellets before and after SPP. By integrating techniques such as end-group titration and liquid chromatography-mass spectrometry (LC-MS)

the study elucidated the patterns of macromolecular weight increase during the SSP process and identified the types of by-products. Methanol extraction experiments indicated that SSP can also lead to a decrease in the content of cyclic PA66

particularly a notable reduction in the cyclic PA66 with repeat unit numbers from 1 to 4. Considering the difficulty in effectively separating various by-products present in PA66 pellets

the spectroscopic characterization methods in this research could identify their signals within complex NMR and MS spectra. This approach promises to establish a foundation for quantitatively calculating by-product content

thereby supporting the optimization of PA66 polymerization and SPP processes and enhancing the quality of PA66 pellets.