  Cloud-point curves of blends of poly(methyl methacrylate) (PMMA) with a
series of oligodiols based on a bisphenol A nucleus and short branches of
poly(ethylene oxide) or poly(propylene oxide) (BPA-EO or BPA-PO), and with PEO
and PPO oligomers, were obtained using a light transmission device.
Experimental results were fitted with the Flory- Huggins model using an
interaction parameter depending on both temperature and composition. For
PMMA/PEO and PMMA/PPO blends, the miscibility increased when increasing the
size of the diol, due to the significant decrease in the entropic and enthalpic
terms contributing to the interaction parameter. This reflected the decrease in
the selfassociation of solvent molecules and in the contribution of terminal OH
groups to the mismatching of solubility parameters. For PMMA/BPA-EO blends, a
decrease of the entropic contribution to the interaction parameter when
increasing the size of the oligodiol was also found. However, the effect was
counterbalanced by the opposite contribution of combinatorial terms leading to
cloud-point curves located in approximately the same temperature range. For
PMMA/BPA-PO blends, the interaction parameter exhibited a very low value. In
this case, the effect of solvent size was much more important on combinatorial
terms than on the interaction parameter, leading to an increase in miscibility
when decreasing the oligodiol size. For short BPA-PO oligodiols no phase
separation was observed. The entropic contribution of the interaction parameter
exhibited an inverse relationship with the size of the oligodiols, independent
of the nature of the chains bearing the hydroxyls and the type of OH groups
(primary or secondary). This indicates that the degree of self-association of
solvent molecules through their OH terminal groups, was mainly determined by
their relative sizes.
