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| - Chain Aggregation Process of Poly(methyl methacrylate) in the MixedSolvent tert-Butyl Alcohol + Water
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| - To study a chain aggregation process, dilute solutions of poly(methyl methacrylate) in themixed solvent tert-butyl alcohol + water (2.5 vol %) with the molecular weight m = 1.57 × 106 werequenched to below the phase-separation temperature and scattered intensities were measured. The light-scattering measurement was carried out in the concentration range from 1.5 × 10-4 to 5.6 × 10-4 g/cm3for a time period of several hours. By using the Guinier plot, the weight-average molecular weight 〈M〉wand z-average square radius 〈R2〉z of clusters of polymer chains were determined as a function of time t(min) and concentration c (g/cm3). The chain aggregation process exhibited an exponential growth of thereduced form 〈M〉w = M(0) exp(gct) with g = 34.8 cm3/(g min), where M(0) is the value extrapolated to t= 0. A double-logarithmic plot of 〈M〉w vs 〈R2〉z1/2 yielded a slightly curved line at small 〈M〉w and approachedthe relation 〈M〉w ∼ 〈R2〉z3/2. These characteristics of the observed chain aggregation process were consistentwith the Smoluchowski equation with the collision kernel (i + j) for i-mer and j-mer, and the relation Rk∼ (mk)1/3 between the radius Rk and the molecular weight mk for k-mer was deduced from an analysis ofthe experimental data based on the Smoluchowski equation. The chain aggregation process observed fora long time period was not explained by a diffusion-limited aggregation mechanism but was explainedby a reaction-limited one.
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