  We analyze a polymerization-induced phase separation taking place in
solutions of a polymer dissolved in a vinyl monomer undergoing an isothermal
free-radical polymerization. The selected system was a solution of
polyisobutylene (PIB) in isobornyl methacrylate (IBoMA). Cloud-point curves for
PIBs of different molar masses were fitted with the Flory-Huggins equation
stated for a 3-component system. Phase separation was analyzed for two
different PIBs at off-critical compositions. Comparing experimental values of
the volume fraction of dispersed phase with those predicted by the coexistence
curves it was found that the system evolved close to equilibrium during an
initial stage. But phase separation stopped at intermediate monomer conversions
as assessed by scanning electron micrographs of partially converted materials.
The evolution of the size distribution of dispersed domains was obtained from
the fitting of light scattering (LS) spectra. Average sizes predicted by LS and
measured in scanning electron micrographs were in rough agreement.
