THE INFLUENCE OF PROCESS VARIABLES ON THE MOLECULAR MASS OF AN/MA COPOLYMERS-II

Viscometry experiments were carried out on a range of laboratory-synthesized polyacrylonitrile precursors that were to be used for the manufacture of PAN/MA hollow-fiber carbon membranes. This was done to determine the effect of the polymerization process variables on the average molecular mass of copolymers of methylacrylate and acrylonitrile. Factors such as the concentrations of methylacrylate monomer (MA) and azo-bis-isobutyronitrile initiator (AIBN), stirrer speed and polymerization temperature were investigated as functions of the molecular mass. An empirical approach that employed statistical experimental designs, used to recognize analytical and statistical methods that translate the process responses into comprehensible terms was used. It was established that hollow-fiber carbon membranes can be reproducibly prepared if the polymerization conditions are controlled. Process variables such as stirrer speed, polymerization temperature, methylacrylate and azo-bis-isobutylonitrile concentrations influence the properties of the copolymer produced and hence the properties of the carbon membranes produced from precursors made from the copolymer. The highest molecular mass PAN was obtained when the concentrations of MA and AIBN were high, while a reduced polymerization temperature favored the synthesis of high molecular mass PAN. The stirrer speed had little or no effect on the molecular mass of the synthesized PAN-based materials. The process variables interactions were statistically processed with the “F-test” method. Interaction between the initiator, AIBN and temperature had a significant effect on the average molecular mass. Monomer MA concentration was of little significance.