A rheological method to characterize the molecular weight changes of polyamide 1012 during solid state polymerization

In this study, a fast and convenient method that can characterize the molecular weight (MW) and its distribution (PDI) of polyamide 1012 after the solid-state polymerization (SSP) was proposed with the rheological technique. Conventionally, polyamides have to be chemically modified to become soluble in an organic solvent suitable for the Gel Permeation Chromatography (GPC) measurement. Herein, to avoid the complex operation of chemical modification, the quantitative correlations between the rheological properties such as zero-shear viscosity, complex viscosity, the frequency and modulus at the crossover point between the storage and loss modulus curves, and the obtained MW and PDI were established. Thus, without chemical modifications, the characterization of PA1012 during SSP becomes convenient and time saving, which is more approach to the real “on-line” control of SSP. The lamellar thickening and SSP occur simultaneously above T g during SSP. Its influence on the final results of SSP was studied. Furthermore, the impact of crystallinity of the raw materials on the SSP behavior was also investigated. The higher crystallinity can lead to a decrease in the SSP rate and final molecular weight and molecular weight distribution.