Chain aggregation processes were studied for dilute solutions of PMMA with the molecular weight m = 1.57 x 10(6) g/mol in the mixed solvent tert-butyl alcohol + water (2.5 vol %) at 25.0 and 30.0 degreesC in the concentration range from 1.4 x 10(-4) to 5.7 x 10(-4) g/cm(3). The weight-average molecular weight (w) and z-average squared radius (z) of Clusters of polymer chains were determined as a function of time by static light-scattering measurements. The phase separation temperature increased from 35.7 to 36.7 degreesC in the concentration range. The aggregation process near the concentration c = 1.46 x 10(-4) g/cm(3) was observed for a time period of about 10 000 min at 25.0 degreesC and 2000 min at 30.0 degreesC. At each temperature both the plots of ln (w) and ln (z) vs t (min) were represented by curved lines. The initial slopes of the lines were proportional to the concentration c. Accordingly, the scaled relations of (w)/M(0) = exp(gct) and (z)/R-2(0) = exp(hct) were obtained at small ct with g = 5.01 cm(3)/(g min) and h = 3.97 cm(3)/(g min) at 25.0 degreesC and with g = 16.9 and h = 13.2 at 30.0 degreesC, where M(0) and R-2(0) are the values extrapolated to t = 0. The reciprocals of gc and he give the characteristic times of the chain aggregation. The longer characteristic times at 25.0 degreesC than at 30.0 were attributed to the effect of the chain collapse. The exponential growth indicated a reaction-limited cluster aggregation of polymer chains. The doublelogarithmic plot of (w) vs (1/2)(z) at each temperature was independent of concentration and represented by a single straight line with the slope D = 2.53 +/- 0.02 at 25.0 degreesC and 2.66 +/- 0.01 at 30.0 degreesC.