Coil-globule transition of poly(methyl methacrylate) in isoamyl acetate

The coli-globule transition was studied by static light scattering measurements on poly(methyl methacrylate) with the molecular weight M-w x 10(-6) = 2.35 and 4.4 in isoamyl acetate. Since the phase separation of the dilute solution occurred very slowly, the measurements could be made in the broad temperature range from near the Theta temperature 61 degrees C to 0 degrees C 30 min after a quench of the solution. The observed expansion factor alpha(2) for the radius of gyration was represented as a function only of tau M-1/2 and showed a constant value at large - tau M-1/2 with tau being 1 - Theta/T. A quantitative comparison between a recent theory for a contracted coli and the data of alpha(2) revealed the coli-globule crossover phenomena. The behavior of plot of 1/alpha(3) versus - tau M-1/2 was distinctly different in the three ranges, i.e., coli range, globule range, and range of a constant alpha. The plot of the observed second virial coefficient A(2) against temperature yielded a minimum as predicted from a theory of A(2) below the Theta temperature.