Suspension ROMP

A typical aqueous suspension polymerization process consists of dispersed monomer droplets and an oil-soluble initiator (50-500 pm). In order to prevent colloidal destabilization, a suspending agent is added to the water in addition to continuous stirring of the monomer dispersion. 

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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... 

ROMP techniques have been used to prepare a family of monomers displaying a single saccharide residue. These hydrophilic monomers 22 have been polymerized under a variety of conditions. Early polymers were prepared by the use of ill-defined RuCI, catalysts. Recently, catalyst 9b was used under a variety of conditions to produce polymers for the required biological studies. Suspension conditions using DTAB as surfactant is required to obtain high molecular weight polymers 23 (Eq. 16). 

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]. 

Differing from 8a and 8b, norbornene-appended HBC 8c (Fig. 10), designed for ROMP, affords nanocoUs as well as nanotubes (Fig. 12) [35]. By choosing appropriate conditions, either nanocoils or nanotubes are selectively formed. For example, by EtzO vapor diffusion into a CH2CI2 solution of 8c (0.65 mM) at 15 °C, the nanocoils form exclusively. At the same time, when the vapor diffusion is conducted at 25 °C at a lower concentration of 8c (0. 22 mM), the nanotubes can be obtained as the sole product. As observed by TEM and SEM, the nanocoil consists of a 20-nm-wide bilayer tape with 30 nm in diameter and 60 nm in pitch (Fig. 13a), while the nanotube possesses a diameter of 20 nm and a wall thickness of 3 nm (Fig. 13b). Interestingly, when the suspension of the nano coils is allowed to stand for 5 days at... 

In this chapter, we present a review of ROMP in dispersed media. ROMP of polymer particles by emulsion, dispersion, and suspension processes will be described. Particular attention will be devoted to the synthesis of functional nanoparticles for advanced materials. In the final part, will review nanoparticle synthesis via self-assembly of ROMP block copolymers. 

ROMP has been reported in emulsion, miniemulsion, dispersion, and suspension. Caution should be used in interpreting reported process types in the literature however, these various processes are not as well defined for nonradical polymerizations as they are for radical polymerizations. In particular, the locus of chain initiation is sometimes ambiguous and the mechanisms of particle nucleation may not be well understood. 

Gnanou s group has extensively explored the use of ROMP in emulsion and miniemulsion in addition to dispersion and suspension. The use of ROMP in tandem with ATRP in miniemulsion has proven to be an effective route for making biphasic or Janus particles, consisting of polynorbornene and poly(methyl methacrylate) domains. They were able to use the same ruthenium-based catalyst for both, achieving simultaneous ROMP of norbornene and ATRP of MMA, using miniemulsion polymerization. Stable latexes with minimal... 

The thus-obtained supported reagent was used for the benzylation of various amines and phenols. Recently, Janda et al. reported on a suspension-type ROMP of mixtures of norborn-2-ene, hydroxymethylnorborn-2-ene and a norborn-2-ene-derived crosslinker for the synthesis of hydroxyl-functionalized spherical supports [177]. After hydrogenation, the support was successfully used for... 

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