Miniemulsion controlled radical polymerization

Controlled Radical Polymerization (ARTP) of Methyl Methacrylate in Miniemulsion... 

Four different approaches for controlled radical polymerization have been adapted to the miniemulsion polymerization process ... 

A review article by Qiu et al. [212] and references herein [217-226] covers NMCRP in miniemulsions up to 2001. Cunningham wrote a related review in 2002, also covering controlled radical polymerization in dispersed phase systems [227]. Here, the main results reported in the Qiu review will be summarized, and new developments in the field since then will be reviewed. 

Using NMP [114, 115] or reversible addition-fragmentation chain transfer (RAFT) [ 119,120,127], agents with ammonium groups for the ion exchange allowed the attachment of initiators on the clay surface for controlled radical polymerizations (NMP, RAFT). Samakande et al. investigated the kinetics of RAFT-mediated living polymerization of styrene [120] and styrene/BA [119] mixtures in miniemulsion. 

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. 

The number of methods and approaches to produce hybrid latexes has increased dramatically in the last 10 years. Not only molecules and latex particles but also surfactant assemblies, block copolymers, and inorganic particles are used as building blocks to create hybrid latex particles. Conventional emulsion polymerization has been studied for the preparation of hybrid latexes already since the early 1980s. In the last decade miniemulsion polymerization turned out to be a valuable alternative for emulsion polymerization. The use of controlled radical polymerization increased the efficiency of the encapsulation process tremendously and added new possibilities to the chain architectures used in the polymeric part of the hybrid latexes. 

Controlled radical polymerization techniques are suitable for synthesizing polymers with a high level of architectural control. Notably, they not only allow a copolymerization with functional monomers (as shown previously for free-radical polymerization), but also a simple functionalization of the chain end by the initiator. Miniemulsion systems were found suitable for conducting controlled radical polymerizations [58-61], including atom transfer radical polymerization (ATRP), RAFT, degenerative iodine transfer [58], and nitroxide-mediated polymerization (NMP). Recently, the details of ATRP in miniemulsion were described in several reviews [62, 63], while the kinetics of RAFT polymerization in miniemulsion was discussed by Tobita [64]. Consequently, no detailed descriptions of the process wiU be provided at this point. 

It should be noted that the application of controlled-radical polymerization (CRP) techniques in emulsion polymerizations has not yet been particularly successful due to the relatively large size of the monomer droplets and insolubility of the radicals generated. However, Charleux and coworkers have reported the utilization of SGI-based alkoxyamines for the emulsion and miniemulsion polymerization of styrenes and acrylates to afford very well-defined and relatively small polymer particles (about 50 nm) (Figure 17.13) (Charleux and Nicolas, 2007). In fact, from a practical point of view very few experimental parameters had to be changed with respect to the classical solution polymerization recipe (Qi et al, 2001 Cunningham, 2002). Indeed, the recent advances in miniemulsion techniques have enabled the... 

Keywords ATRP Capsules Composite materials Controlled radical polymerization Emulsion polymerization Encapsulation Inorganic particles Miniemulsion polymerization NMP RAFT... 

Vesicle-Templated Controlled Radical Polymerization An Alternative to Miniemulsion... 

Living free-radical polymerization represents a promising technique to produce polymers with highly controlled structures. Different possible systems known from bulk polymerizations have been used in miniemulsions. The living free radical polymerization of, e.g., styrene via the miniemulsion approach allows one to eliminate the drawback of the bulk system where an increase in polydis-persity was found at high conversions due to the very high viscosity of the reaction medium [90]. 

Cunningham and coworkers [65-68] have completed detailed modeling of nitroxide mediated radical polymerization in miniemulsion. They found that issues of distribution of the control agent between the aqueous and organic phases can be critical to maintaining livingness. 

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. 

Luo YW, Gu HY (2006) A general strategy for nano-encapsulation via interfaciaUy confined living/controlled radical miniemulsion polymerization. Macromol Rapid Commun 27 21-25... 

Qi, G. Eleazer, B. Jones, C.W. Schork, F.J. Mechanistic aspects of sterically stabilized controlled radical inverse miniemulsion polymerization. Macromolecules 2009, 42 (12), 3906-3916. 

Keywords Controlled/living radical polymerization Core-shell particle Dispersion polymerization Emulsion polymerization Grafting from Hybrid Miniemulsion polymerization Nanogel Nanoparticle... 

Initiators for the controlled living radical polymerization could also be introduced to silica particles. Nitroxide-mediated polymerization (NMP) conducted with styrene in miniemulsion led to the generation of core-shell particles, with styrene grafted to the central silica particle [131]. PBA could be polymerized from 20 nm silica beads by attaching an ATRP agent to the silica surface and subsequent miniemulsion polymerization [132]. Confining the polymerization to miniemulsion droplets could avoid gel formation, which was observed in the bulk reaction. Due to the limited monomer diffusion, only 25-35% of conversion could be obtained in bulk. 

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