Kinetics and mechanisms of acrylamide polymerization from absolute, onlinemonitoring of polymerization reaction

An automatic, continuous, online monitoring technique was used to follow th e polymerization of acrylamide under a variety of temperature and initiator conditions, without chromatographic columns. The technique furnishes, as a function of time, the weight-average polyacrylamide mass M-w, the monomer conversion, reduced viscosity, and certain measures of polydispersity. Afte r a complex initial phase following initiator addition, wherein impurities competed with monomer for free radicals, monomer conversion followed a firs t-order decay during most of the subsequent reaction. For fixed monomer con centration, at every point in conversion beyond very early points, M-w was proportional to the inverse square root of the initiator concentration. Fur thermore, the monomer decay time also scales in the same way, and M-w vs co nversion is linear during most of the conversion, with a negative slope. He nce, the overall reaction scheme falls within the quasi-steady state approx imation (QSSA) of ideal polymerization kinetics. The rate constant for init iator decay, as well as the ratio of propagation rate constant squared to t ermination rate constant were determined. The activation energy for the pot assium persulfate initiator decomposition was also determined. Deviations f rom the ideal kinetics at early and late conversion are rationalized by exi sting models. Using a technique for determining instantaneous polydispersit y from the derivative of M-w, it was possible to follow the evolution of th e polydispersity for the polyacrylamide reactions.