Transition from a chain-collapse process to a chain-aggregation process of poly(methyl methacrylate) in a mixed...

The transition from a chain-collapse process to a chain-aggregation process was studied by static light scattering on poly(methyl methacrylate) of the molecular weight mw=1.22x10(7) in the mixed solvent tert-butyl alcohol+water (2.5 vol%). The concentration c of the solutions ranged from 0.5 to 2.5x10(-4) g/cm3 and the measurement was carried out at appropriate time intervals up to the time t(h)=3250 after the quench to 35.0 degrees C which was a few degrees below the phase separation temperature. The molecular weight Mw and mean-square radius of gyrationz were estimated from each scattering curve determined at the finite concentrations. At the initial stage of 100 h, z decreased rapidly with the time t indicating the chain collapse, while at the later stage of 3000 h, z increased very slowly indicating the chain aggregation. The chain-collapse process and chain-aggregation process could be analyzed separately, though the two processes overlapped appreciably at the higher concentrations. The former process depended slightly on the concentration, while the latter process showed the exponential growth of ln Mw approximately ct and lnz approximately ct. In the plot of lnz versus ln Mw, the chain-collapse process was depicted by different lines depending on the concentration, while the chain-aggregation process was described by a single straight line. The transition from the former to the latter process occurred distinctly near 200 h after the quench irrespective of the concentration.