Kinetics of coil-globule collapse in poly(methyl methacrylate) in dilute solutions below Θ temperatures

The time dependence of coil-globule collapse in atactic poly(methyl methacrylate) samples having molecular weights 6.5 x 10(6) and 3.3 x 10(6) g/mol dissolved in isoamyl acetate and n-butyl chloride were studied by dynamic light scattering. For example, a dilute solution of PMMA (6.5 x 10(6) g/mol) in isoamyl acetate was quenched from 61 degrees C (Theta temperature) to 18.5 degrees C. As a result, the measured hydrodynamic radius ([R-h]) was reduced from 42 +/- 2 to 15 +/- 2 nm. For the cells used in these DLS measurements the thermal equilibration time was found to be about 20 s. The transition from coil to globule in this cell was observed to take place in almost 35 s. We have found the coil-to-globule transition time to be inversely related to the depth of quench (Delta T) of the process. This transition time also increases with increase in molecular weight of the polymer chain.