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

Abstract

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.