Suspension polymerization with ATRP

There are limited reports of ATRP in suspension polymeriza-tion, " including their use for encapsulating polar organic solvents. " As with NMP, suspension polymerizations with larger particle sizes tend to behave similar to bulk polymerizations, with issues such as catalyst partitioning not as problematic as when particle diameters are in submicrometer range. 

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... 

RAFT, allowing for predictable molecular weight with low polydispersi-ties, is applicable to a wide range of vinyl monomers [173-176], some of them not always being polymerizable by NMP or ATRP (i.e., VAc [167] or monomers bearing protonated acid groups). Hence, RAFT is employed in many polymerization processes, such as bulk, solution, suspension, emulsion, and miniemulsion [177-180]. 

Taking into account all of the above mentioned applications, the synthesis of magnetic latex will be discussed in two parts first, the preparation of iron oxide nanoparticles and, second, the preparation of magnetic latex. Depending on the aim of researchers, many polymerization techniques are applied such as suspension, dispersion, emulsion, microemulsion and miniemulsion polymerization in combination with controlled radical polymerization techniques like atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) and nitroxide-mediated radical polymerization (NMP). The preparation of hybrid magnetic latex by emulsion polymerization will be the focus of this review. 

Living polymerization in water also led to polymers with a relatively narrow molecular mass distribution (1.1-1.3) and molecular masses, which showed linear increase with conversion, indicating the living character of this polymerization [320]. Recently, Matyjaszewski et al. reported both reverse and direct ATRP of n-butyl methacrylate in an aqueous dispersed system via the miniemulsion approach, characterized by a linear increase of the molecular mass with conversion and a narrow distribution of molecular masses [321]. The suspension-type process of living polymerization of MMA in water not only led to well controlled and high molecular masses and low PDIs, but also the polymerization proceeded without the addition of Al(0-i-Pr)3 and clearly faster than ATRP in organic solvents [322]. 

In ATRP, there are reactive and dormant polymer species in equilibrium during the polymerizations, which alternate between halide-capped polymers (dormant) and growing (reactive) polymers with a free radical on the end. The choice of catalyst controls this equilibrium which in turn influences the polymerization rate and the distribution of chain lengths. The mechanism offers flexibihty to conduct reactions in bulk, solution, or emulsions/suspensions, just as fiee-radical polymerizations. Due to the capability to polymerize a large range of monomers with an inexpensive catalyst in a reactor, where purity is nearly as important as in anionic polymerizations, ATRP continues to grow in popularity. For further information, review articles written by the inventors are available [12,16]. 

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