Polymerization in heterogeneous media

Among the large variety of systems applied to carry out free-radical polymerization in heterogeneous media, emulsion polymerization is the most... 

Polymerization in heterogeneous media offers many advantages. Among them are easier heat removal, better viscosity control, and easier recovery of the polymer products. Moreover, today s environmental concerns can be better addressed through the use of nonflammable, low-cost, and environmentally friendly solvents, ideally water. 

A broad range of polymers are produced by polymerization in heterogeneous media, including polyolefins manufactured by slurry (high density polyethylene and isotactic polypropylene) and gas phase (linear low density polyethylene and high density polyethylene) polymerization coatings and adhesives produced by emulsion and miniemulsion polymerization flocculants obtained by inverse emulsion and microemulsion polymerization poly(vinyl chloride) (PVC) and polystyrene produced by suspension polymerization and toners synthesized by dispersion polymerization. As a whole, they represent more than 50% of the polymer produced worldwide [1]. 

Many manufacturing methods are available for the synthesis of latex particles exhibiting appropriate functionalities and three main approaches can be followed (a) polymerization in heterogeneous media (b) modification of preformed particles (see Arshady, 1999) (c) formulation of colloidal dispersions from preformed polymers. 

Polymer latex nanoparticles can be prepared in many materials such as polystyrene and acrylate with controllable size, through radical-initiated polymerization in heterogeneous media (Figure 14.2). The sizes of latex nanoparticles are very dependent on the polymerization conditions. To yield nanosized particles, the polymerization is usually carried out in miaoemulsions [34], For some applications, two or more monomers are used. For example, for polystyrene nanoparticles, divinylbenzene (DVB) is used as a cross-linker to improve the structural performance [35] and methacrylic acid (MAA) or methacrylate (MMA) is used as a co-monomer to provide the nanoparticles with desirable surface chemistry [36,37], Furthermore, some fluorochromes or magnetic materials are incorporated into polymer nanoparticles, to render the particles multifunctional [38,39],... 

Many polymerizations are carried out in heterogeneous media, usually water-monomer mixtures, where suspending agents or surfactants ensure proper dispersion of the monomer and control the particle size of the product. 

NMP of S in heterogeneous media is discussed in reviews by Qiu et at.,205 Cunningham,206 207 and Schork et a/.208 There have been several theoretical studies dealing with NMP and other living radical procedures in emulsion and miniemulsion."09 213 Butte et nr/.210 214 concluded that NMP (and ATRP) should be subject to marked retardation as a consequence of the persistent radical effect. Charlcux209 predicted enhanced polymerization rates for minicmulsion with small... 

With specific reference to heterogeneous polymerizations in supercritical media, several oversimplified pseudo-homogeneous descriptions have been occasionally applied aimed at estimating kinetic parameters or elucidating dominant mechanisms [5, 6, 13, 14, 31]. The first (and probably only) comprehensive... 

Many polymerizations are performed in heterogeneous media, so that the final polymer product is obtained as a particulate material. The characteristics of the final particle size distribution (PSD) of the product maybe of fundamental importance for many applications. 

Control of radical poljmerization with the addition of thiocarbonylthio compounds that serve as reversible addition fragmentation chain transfer (RAFT) agents was first reported in 1998. Since that time much research carried out in these laboratories and elsewhere has demonstrated that RAFT polymerization is an extremely versatile process.f It can be applied to form narrow polydispersity poljmers or copolymers from most monomers amenable to radical poljmerization. It is possible to take RAFT poljmerizations to high conversion and achieve commercially acceptable polymerization rates. Polymerizations can be successfully carried out in heterogeneous media (emulsion, miniemulsion, suspen-... 

Extension Toward Heterogeneous Polymerization in Dispersed Media... 

Besides polymerization in dispersed media as described in Section 10.4, another form of heterogeneous polymerization involves the use of a solid catalyst. The most commonly known examples are Ziegler-Natta and Phillips catalysts for the production of polyethylene products (Tobita and Yanase, 2007). In this section, the most frequently applied modeling approaches for the calculation of the polymer microstructure in such polymerization processes are highlighted, neglecting macroscale effects for simplicity. For a more detailed description, the reader is referred to Asua (2007) and Tobita and Yanase (2007). 

Qiu, J., Charleux, B., and Matyjaszewski, K. (2001). Controlled/living radical polymerization in aqueous media homogeneous and heterogeneous systems. Prog. Polym. Sci., 26(10) 2083-2134. 

The second large group of chapters spedfically describes the synthetic aspects of ROP/ROMP. In this section, the architecture of polymers prepared by ROMP, functionalization of poly (ethylene oxide), chain extension by ROP, nonlinear polyethers, as wdl as ROP in heterogeneous media are discussed. It also describes methods of polymerization that provide regular and mostly spherical partides, and gives for the first time a review of the kinetics and mechanism of this particular system that resembles emulsion vinyl polymerization. The chapter on polymerization in confined space (encompassing matrix polymerization) summarizes results that may open the way to the replica polymerization, a process that is typical for the matrix synthesis of biomacromolecules in nature. 

Much has now been written on the use of RAFT in emulsion and miniemulsion polymerization, and many reviews relating to the use of RAFT in heterogeneous media have appeared. Our first communication on RAFT polymerization briefly mentions the successful emulsion polymerization of butyl methacrylate with cumyl dithiobenzo-ate as a table entry. Additional examples and brief discussion of some of the important factors for successful use of RAFT polymerization in emulsion and miniemulsion were provided... 

In the first section, various kinds of functional polymer, in particular the most used conductive polymer, conjugated polymer (CP), redox polymer, metallopolymer. Selection of the correct functional polymer depends on the desired properties of the resulting nanocomposites. The second part of the chapter focuses on the basic approaches used in the preparation of polymeric nanoparticles. As mentioned earlier, there are two basic approaches in the recent literature to synthesize the polymeric nanoparticles. In this section, we focus on the discussion of the common and widely used preparation methods for various kinds of polymeric nanoparticles. The polymerization method is based on the encapsulation of nanoparticles through heterogeneous polymerization in dispersion media. This method can be further classified into emulsion, microemulsion and miniemulsion. Polymer encapsulated nanoparticles can also be prepared directly from preformed polymer, where this approach is based on the specific interactions between nanoparticles and the preformed polymer, such as electrostatic interactions, hydrophobic interactions and secondary molecular interactions or self-assembly method. 

Synthesis of Nanocapsules and Polymer/ Inorganic Nanoparticles Through Controlled Radical Polymerization At and Near Interfaces in Heterogeneous Media... 

In perchloric acid media the reaction is extremely slow and is complicated by the formation of polymeric species of tin, and by heterogeneity. Rabideau has examined the kinetics in mixed perchlorate-chloride solutions, in which media no turbidity is apparent. The rate expression is complex, viz. 

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