Kinetics of coil–globule transition of poly(methyl methacrylate) in isoamyl acetate

The kinetics of coil–globule transition was studied by static light scattering measurements on poly(methyl methacrylate) with the molecular weight Mw×10−6=8.4 and 12.2 in isoamyl acetate. Since the phase separation of the solution occurred very slowly, the mean-square radius of gyration of the polymer could be determined for a long time after quench to far below the θ-temperature 61 °C. The expansion factor α2 observed 30 min after quench to below the coil–globule crossover point, deviated largely from theoretical predictions, and was found to be a transient one. Chain collapse processes were measured in the time range from 30 min to a few thousand min after the quenches to 30 °C and 45 °C for Mw=12.2×106 and to 30 °C for Mw=8.4×106. The expansion factor in each process approached a constant value αeq2 in the time range. The collapse process was expressed as a function of time t(min) by α2=α∞2+{b/(t+c)}p, where b, c, p, and α∞2 were constant, independent of time. In all the three processes the constants had values near p∼0.5, b∼0.4, c∼0.6, and α∞2 was slightly smaller than αeq2. The constant c was introduced to satisfy the initial condition of α2=1 at t=0. This behavior of α2(t) and a comparison with kinetic theories of chain collapse concluded that the chain collapse occurred in a single stage process without formation of chain knots.