  An unexpected experimental finding is reported where the primary morphology
developed during polymerization-induced phase separation in a rubber-modified
thermoplastic disappears at high conversions. This process was evidenced by
light scattering (LS) and scanning electron microscopy (SEM) for a particular
composition of solutions of polyisobutylene oligomers (PIB) in
isobornylmethacrylate (IBoMA), during the free-radical polymerization of the
monomer. The primary phase separation produced a dispersion of domains rich in
PIB containing significant amounts of the monomer (IBoMA). Polymerization of
the monomer in these domains occurred at high overall conversions producing the
filling of dispersed domains with a PIBoMA-PIB blend. Under these conditions
the final material had the appearance of a homogeneous blend. The process might
be adapted to produce new types of rubber-modified thermoplastics where rubber
particles are replaced by rubber-rich domains that do not exhibit definite
boundaries. Keywords:
