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

Abstract

The coil-globule transition was studied by static light scattering measurements on poly(methyl methacrylate) with the molecular weight $M_w\times {10}^{-6}=2.35\mathrm{}$ 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 Θ temperature 61 °C to 0 °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 τ being $1-\Theta /T.\mathrm{}$ A quantitative comparison between a recent theory for a contracted coil and the data of ${\alpha }^2$ revealed the coil-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., coil range, globule range, and range of a constant α. 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 Θ temperature.