Coil-globule transition of poly(methyl methacrylate) in a mixed solvent

From light scattering measurements the coil-globule transition has been observed for poly(methyl methacrylate) in the mixed solvent water+tert-butyl alcohol with molecular weight Mw=2.38×{}10⁶. Since the phase separation occurred very slowly for this system, the mean square radius of gyration 〈s²〉 and the second virial coefficient A₂ were determined reliably even far below the phase-separation temperature. A comparison of the observed 〈s²〉 with a theory for a contracted coil confirmed the coil-globule transition. The observed second virial coefficient had a minimum in the temperature region where 〈s²〉 approaches the value for the globule state.