Emulsion ROMP

Early attempts at emulsion ROMP systems have been reported. These systems, however, either fail for many monomers or, at best, give low yields of polymer (typically less than 9%). See Rinehart RH, Smith HP (1965) J Polym Sci, Polym Lett 3 1049... 

Rinehart et al. [1, 2] and Michelotti and Keaveney [3] reported the first successful emulsion ROMP using water-soluble ruthenium, iridium, and osmium chlorides activated by a reducing agent. These ill-defined catalyst systems were... 

ROMP) of functionalized oxanorbornenes in water, methanol and aqueous emulsions, but have not yet been used in RCM. 

For the synthesis of carbohydrate-substituted block copolymers, it might be expected that the addition of acid to the polymerization reactions would result in a rate increase. Indeed, the ROMP of saccharide-modified monomers, when conducted in the presence of para-toluene sulfonic acid under emulsion conditions, successfully yielded block copolymers [52]. A key to the success of these reactions was the isolation of the initiated species, which resulted in its separation from the dissociated phosphine. The initiated ruthenium complex was isolated by starting the polymerization in acidic organic solution, from which the reactive species precipitated. The solvent was removed, and the reactive species was washed with additional degassed solvent. The polymerization was completed under emulsion conditions (in water and DTAB), and additional blocks were generated by the sequential addition of the different monomers. This method of polymerization was successful for both the mannose/galactose polymer and for the mannose polymer with the intervening diol sequence (Fig. 16A,B). 

Although solution polymerizations are typically employed, ROMP can also be carried out by bulk, emulsion, and suspension polymerization, and in a number of reaction media. Reaction efficiencies, molecular weights, and PDI values for ROMP of NBE and COE in supercritical CO2 using 10b, 22b, and 33a were generally similar to those... 

Hydrates of RUCI3, IrCl3, and OSCI3 are suitable catalysts for the ROMP of norbomene in aqueous and alcoholic solvents. Ruthenium trichloride hydrate is used for the industrial production of poly(norbornene). These hydrates act for the ROMP of norbomene and norbomene derivatives in pure water through an emulsion process (18). 

Derivatives of acyclic olefins can be used as chain transfer agents in these polymerizations. The most effective are those with a terminal double bond. For example, in the ROMP of 248 catalysed by [Ru(H20)6](0Ts)2 the transfer constant (klr/kp) for CH2=CHCH2CH20H is 0.21. The size of the polymer particles produced by emulsion polymerization of 248, using RUCI3 with a non-ionic surfactant, is of the order of 0.03 /zm577. 

Claverie et al. [325] have polymerized norbornene via ROMP using a conventional emulsion polymerization route. In this case the catalyst was water-soluble. Particle nucleation was found to be primarily via homogenous nuclea-tion, and each particle in the final latex was made up of an agglomeration of smaller particles. This is probably due to the fact that, unlike in free radical polymerization with water-soluble initiators, the catalyst never entered the polymer particle. Homogeneous nucleation can lead to a less controllable process than droplet nucleation (miniemulsion polymerization). This system would not work for less strained monomers, and so, in order to use a more active (and strongly hydrophobic) catalyst, Claverie employed a modified miniemulsion process. The hydrophobic catalyst was dissolved in toluene, and subsequently, a miniemulsion was created. Monomer was added to swell the toluene droplets. Reaction rates and monomer conversion were low, presumably because of the proximity of the catalyst to the aqueous phase due to the small droplet size. 

In summary, this pioneering work clearly demonstrated the possibility of aqueous catalytic insertion polymerization of acyclic and cyclic olefins, as well as aqueous ROMP. On the other hand, metal salts without any additional ligands to control the properties of the metal centers were utilized, and activation to the active species was probably also relatively ineffective in most cases. Consequently, catalyst efficiencies were moderate at best. Most of the polymerizations also afforded low molecular weight materials, or employed rather special monomers. The possibility of polymer latex synthesis appears not to have received much attention, although free-radical emulsion polymerization of styrene and butadiene was already a large-scale process at the time. 

ROMP of norbornene in aqueous emulsion employing ruthenium(IV) complexes [117] with bis(allyl) ligands such as the water-soluble [(// // -CioHi6)Ru(OH2)(OAc)]BF4 as catalyst precursors has been reported by Wache [118]. High molecular weight polymer with an unusually high cis content was obtained at rates of 100 TO h . ... 

The lessons learned from these complexes were eventually applied to the synthesis of well-defined ruthenium alkylidenes 8 and 9. Although they were insoluble in water, these alkylidenes could be used to initiate the living ROMP of functionalized norbornenes and 7-oxanorbomenes in aqueous emulsions. Substitution of the phosphine ligands in 9 for bulky, electron-rich, water-soluble phosphines produced water-soluble alkylidenes 10 and 11, which served as excellent initiators for the ROMP of water-soluble monomers in aqueous solution. These new ruthenium alkylidene complexes are powerful tools in the synthesis of highly functionalized polymers and organic molecules in both organic and aqueous environments. 

Rinehart et al. have reported ROMP of norbornene and of 2-functionalized nor-born-5-enes with polar ester moieties in aqueous emulsion with moderate activities. Iridium(III) or iridium(IV) salts in combination with a reducing agent, or Ir1 alkene complexes, were employed as catalyst precursors [32, 55],... 

Due to the water insolubility of these metal carbenes, aqueous polymerizations represent heterogeneous multiphase mixtures. Investigation of ROMP of the hydrophilic monomer 8 or of a hydrophobic norbomene in aqueous emulsion (catalyst precursor 7 b added as methylene chloride solution) or suspension demonstrated that the polymerization can occur in a living fashion. For example, at a monomer to catalyst ratio 8/7b = 100 with 78% yield, poly-8 of Mw/Mn 1.07 vs. polystyrene standards was obtained [68]. Using water-soluble carbene complexes of type 9 and water-soluble monomers 10, living polymerization can be carried out in aqueous solution, without the addition of surfactants or organic co-solvents [69]. 

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