Synthesis of high molecular weight nylon 46 in supercritical carbon dioxide

摘要

Nylon 46 with high molecular weight was successfully synthesized in supercritical carbon dioxide (sc-CO_2) by one-step three-stage polymerization using the salt prepared from 1,4-diaminobutane and 1,6-adipic acid as a monomer. The polymerization process was divided into three reaction stages: precondensation, postcondensation, and vacuum. To prepare high molecular weight nylon 46, the precondensation of the salts with pH over 7.23 was first carried out at 190 ° under 30 MPa for 2 h. Then CO_2 in the reactor was exhausted along with removing byproduct water, and the reactor was refilled with dry liquid CO_2. Subsequently, the prepolymer formed was subjected to the postcondensation at 280 ° for 3 h under 15 MPa. Finally, the reactor was heated in vacuum at 270-280 ° for 30-45 min. The highest viscosity-average molecular weight of the nylon 46 sample synthesized from the above process is 48200 g/mol. The chemical structure and thermal properties of the nylon 46 were characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The nylon 46 sample, as an example, has melting point of 310 °, glass transition temperature of 67 °, starting decomposition temperature of 400 °, and maximum decomposition rate at 450 °.