142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

162 K. Ito, S. Kawaguchi
to the latex surface on pH, degree of neutralization, and salt concentration have
been the subject of a growing experimental and theoretical effort.
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In all instances of the dispersion polymerization, amphiphilic graft copolymers
produced in a selective solvent for the branches play a crucial role. They act
as a steric stabilizer to provide colloidal stability to the system by adsorbing or
becoming incorporated into the surface of the newly formed, precipitated polymers.
Schematically, a microsphere thus obtained by copolymerization with a
small amount of macromonomer has a core-shell structure as given in Fig. 5,
with the core occupied by the insoluble substrate polymer chains and the shell
by the soluble, graft-copolymerized macromonomer chains. The backbone
chains of the graft copolymers, which must be insoluble in the medium, serve as
the anchors into the core. The following section presents a general criterion for
the size control of polymeric microspheres by the dispersion copolymerization
using macromonomers.
Fig. 5. Schematic picture of a microsphere obtained in emulsion and dispersion copolymerization
using macromonomer technique. The grafted chains are exaggerated in size