Small-angle neutron scattering studies of inhomogeneities in latex particles from emulsion homopolymerizations

Small-angle neutron scattering experiments were carried out to examine the extent of monomer/ polymer spatial inhomogeneities in latex particles formed in an emulsion homopolymerization, using contrast variation and isotopic labeling systems to look at the morphology of swollen and two-stage latices. Samples covered a range of molecular weights including systems where the radius of gyration of the polymer chains was both comparable to and smaller than the particle size. The experiments were designed to test separately inhomogeneities arising from two different effects: (1) the "repulsive wall" (thermodynamic) effect arising from the decrease in entropy of a polymer chain confined near the surface of a particle (the experiments here examined polymer distribution in polystyrene particles swollen with toluene); (2) "surface anchoring" (largely kinetic) arising mainly because, with a water-soluble initiator, free radicals enter latex particles at the surface (here experiments examined the distribution of newly formed polymer in seeded growth; related to this are inhomogeneities arising from finite rates of diffusion of monomer and of polymer). Results support the conclusion that repulsive wall effects do not give rise to significant nonuniformities but that inhomogeneities may arise in the final product where the polymer chain dimensions are substantially less than the particle radius. The latter conclusion is consistent with predictions of the surface anchoring model

General discussion

SCOPUS: no.jinfo:eu-repo/semantics/publishe