Ring-opening metathesis polymerization in emulsion

Ring-opening metathesis polymerization (ROMP) of norbornene (NBE), catalyze d by water-soluble ruthenium alkylidenes 1, RuCl2(PCy2(C5H10NMe2Cl))(2)(=CH Ph), or 2, RuCl2(TPPTS)(2)(=CHCO2Et) (TPPTS = tris(3-sulfonatophenyl)phosph ine, sodium salt), has been carried out in emulsion. Polynorbornene latexes (PNBE) can be obtained in high yields, in the absence of floc, and with hi gh solids, if Dowfax is used as surfactant. The nucleation mechanism of the polymerization has been found to be a continuous homogeneous nucleation. T he resulting polymer particles are formed of aggregates of small primary pa rticles, stabilized by the highly ionized chain ends. Typical particle size s are ranging from 50 to 100 nm, even at higher solids. Less strained olefi ns, such as cyclooctene, COE, and 1,5-cyclooctadiene, GOD, cannot be effici ently polymerized by catalysts 1 or 2. Nevertheless, these monomers are pol ymerized by a hydrophobic catalyst, 3, RuCl2(PCy3)(2)(=CHPh). To form collo idal objects, the catalyst is dispersed into water through the use of a min iemulsion technique. The miniemulsion is then fed with monomer, and after p olymerization, a latex is obtained. Monomer conversion is moderate, but a l atex is generated in the absence of floc.