Non-Aqueous Suspension Polycondensation for the Preparation of Poly(p-phenylene terephthalamide)

A non-aqueous suspension polycondensation method was proposed to proceed the reaction of p-phenylenediamine and terephthaloyl chloride for the preparation of poly(p-phenylene terephthalamide) (PPTA). The system was operated with NMP-CaCl₂ solution as dispersed phase and inert liquid paraffin as continuous phase. Each of NMP-CaCl₂ solution microdroplets suspended in paraffin serves as a microreactor where the polycondensation takes place. Effects of a number of influencing variables affecting PPTA molecular weight were studied experimentally in vessels, including the phase ratio of NMP/paraffin, reaction time, stirring rate, CaCl₂ concentration, monomer concentration, monomer molar ratio and temperature. PPTA with the highest weight-average molecular weight of 18,000 were obtained in the experiment. This two-phase polycondensation system brings many advantages, including sealed reaction environment keeping reactants away from oxygen and water, easy removal of HCl to promote the reaction, well-controlled temperature and low viscosity with less energy cost. We have also preceded the polycondensation in a microreactor continuously, and compared the results in the batch process.