Ethylene polymerization catalyzed by nickel(II) keto-ylide complexes has been performed in water to yield a latex of linear PE. Colloidal stability is highly enhanced by the use of a miniemulsion technique to disperse the catalyst prior contact with the monomer. Latex of typically 200 nm particle diameters and up to 10% solids are generated by this method. The influence of several factors (temperature, pressure, solids) onto the polymerization is studied in detail. The surfactant adsorption isotherms onto these highly crystalline and nonpolar particles are also presented.
Ring-opening metathesis polymerization (ROMP) of norbornene (NBE), catalyzed by water-soluble ruthenium alkylidenes 1, RuCl2(PCy2(C5H10NMe2Cl))2(CHPh), or 2, RuCl2(TPPTS)2(CHCO2Et) (TPPTS = tris(3-sulfonatophenyl)phosphine, sodium salt), has been carried out in emulsion.
Polynorbornene latexes (PNBE) can be obtained in high yields, in the absence of floc, and with high
solids, if Dowfax is used as surfactant. The nucleation mechanism of the polymerization has been found
to be a continuous homogeneous nucleation. The resulting polymer particles are formed of aggregates of
small primary particles, stabilized by the highly ionized chain ends. Typical particle sizes are ranging
from 50 to 100 nm, even at higher solids. Less strained olefins, such as cyclooctene, COE, and
1,5-cyclooctadiene, COD, cannot be efficiently polymerized by catalysts 1 or 2. Nevertheless, these
monomers are polymerized by a hydrophobic catalyst, 3, RuCl2(PCy3)2(CHPh). To form colloidal objects,
the catalyst is dispersed into water through the use of a miniemulsion technique. The miniemulsion is
then fed with monomer, and after polymerization, a latex is obtained. Monomer conversion is moderate,
but a latex is generated in the absence of floc.
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