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

The time dependence of coil-globule collapse in atactic poly(methyl methacr ylate) samples having molecular weights 6.5 x 10(6) and 3.3 x 10(6) g/mol d issolved in isoamyl acetate and n-butyl chloride were studied by dynamic li ght 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 red uced from 42 +/- 2 to 15 +/- 2 nm. For the cells used in these DLS measurem ents the thermal equilibration time was found to be about 20 s. The transit ion 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 rel ated to the depth of quench (Delta T) of the process. This transition time also increases with increase in molecular weight of the polymer chain.