Kinetics of chain aggregation of poly(methyl methacrylate) in isoamyl acetate

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For dilute solutions of poly(methyl methacrylate) in isoamyl acetate with the molecular weight Mw=2.35×106, the phase separation process was observed as an aggregation process of polymer chains by light-scattering measurements. The aggregation process was measured for a period of hours at four polymer concentrations and at about 15 K below the phase separation temperature. The light-scattering data analysis by Guinier plot yielded the average molecular weight 〈M〉w and radius 〈R2〉z1/2 for polymer aggregates as a function of time t and revealed the exponential growth of 〈M〉w∼egt and 〈R2〉z∼eht. The coefficients g and h were proportional to the polymer concentration. A shape of the observed scattering function was independent of the concentration and time. The fractal dimension for 〈M〉w∼〈R2〉zD/2 was determined to be D=2.86±0.03. These characteristic features of the polymer aggregation were represented by the Smoluchowski equation for cluster–cluster aggregation with the collision kernel (i+j) for imer and jmer. The observed scattering function and fractal dimension were analyzed by the Smoluchowski equation with the assumed value D=3 for monodisperse clusters.