Chain Aggregation Process of Poly(methyl methacrylate) in the Mixed Solvent tert-Butyl Alcohol + Water

Abstract

To study a chain aggregation process, dilute solutions of poly(methyl methacrylate) in the mixed solvent tert-butyl alcohol + water (2.5 vol %) with the molecular weight m = 1.57 × 106 were quenched 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/cm3 for a time period of several hours. By using the Guinier plot, the weight-average molecular weight 〈M〉w and 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 the reduced 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 approached the relation 〈M〉w ∼ 〈R2〉z3/2. These characteristics of the observed chain aggregation process were consistent with 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 of the experimental data based on the Smoluchowski equation. The chain aggregation process observed for a long time period was not explained by a diffusion-limited aggregation mechanism but was explained by a reaction-limited one.