A method for online monitoring of polydispersity during polymerization reactions

Building on a recently introduced technique for continuous online monitorin g of absolute weight-average molecular weight M-w of polymers during polyme rization reactions, a method is introduced here for finding a useful approx imation to the polymer mass distribution and moments at each instant during the reaction. The method is based on finding the instantaneous weight-aver age mass at each instant, M-w,M-inst, from an expression involving the deri vative of the cumulative M-w, which is directly monitored online. The metho d is restricted to chain growth polymerization where individual chains are produced and terminate rapidly compared to the overall time it takes for co mplete monomer conversion to polymer. Data from two different polymerizatio n experiments that were monitored online were then analyzed. One of these e xperiments is from a reaction for poly(vinylpyrrolidone), which produced a bimodal population, and the other from a reaction that produced a broad, un imodal distribution. Finally, other possibilities for online polydispersity measurements are briefly discussed.