Emulsion polymerization polymer synthesis

Product Identification was by GC/MS, NMR, and IR. Fundamental crosslinking chemistry was explored using swell measurements on simple solution copolymers and swell and tensile measurements with vinyl acetate (VAc), vinyl acetate/butyl acrylate (VAc/BA) or vinyl acetate/ethylene (VAE) emulsion copolymers. Polymer synthesis 1s described In a subsequent paper (6). Homopolymer Tg was measured by DSC on a sample polymerized In Isopropanol. Mechanistic studies were done 1n solution, usually at room temperature, with 1, 2 and the acetyl analogs 1, 2 (R =CH3). 

Uniform macroporous polymer particles have been prepared in the size range of 5-20 iitm by the multistage emulsion polymerization methods. Several methods are available in the literature describing the synthesis and the properties of macroporous uniform particles. The main steps of these methods may be summarized as follows. 

A research group in Lehigh University has extensively studied the synthesis and characterization of uniform macroporous styrene-divinylbenzene copolymer particles [125,126]. In their studies, uniform porous polymer particles were prepared via seeded emulsion polymerization in which linear polymer (polystyrene seed) or a mixture of linear polymer and solvent were used as inert diluents [125]. The average pore diameter was on the order of 1000 A with pore volumes up to... 

Bradley M, Grieser F (2002) Emulsion polymerization synthesis of cationic polymer latex in an ultrasonic field. J Colloids Interface Sci 251 (1) 78—84... 

Since microgels are intramolecularly crosslinked macromolecules of colloidal dimensions, it is necessary for their synthesis to control the size of the growing crosslinked molecules. This can be achieved by carrying out polymerization and crosslinking in a restricted volume, i.e. that of a micelle or of a polymer coil. Thus, two general methods of microgel synthesis are available (1) emulsion polymerization, and (2) solution polymerization. 

As another case study a process synthesis of an emulsion polymerization process is given (Hurme and Heikkila, 1998). In emulsion polymerization unsaturated monomers or their solutions are dispersed in a continuous phase with the aid of an emulsifier and polymerized. The product is a dispersion of polymers and called a latex. The raw materials are highly flammable unsaturated hydrocarbons and the reaction is exothermic which both cause a risk. The main phases and systems in an emulsion polymerization plant are listed in Table 31. 

C02-philic molecules have been utilized for the design of metal-mobilizing ligands to be used in SCCO2 [67-69,135-137], e.g., as shown in Fig. 7a [55] and for the synthesis of surfactants that form micelles, emulsions, and micro emulsions in CO2, e.g., as shown in Fig. 7b. [70] Polymer solubility in SCCO2 has been studied [71] and utilized for polymer synthesis [72-74]. Recently, DeSimone and co-workers synthesized high-molar-mass fluoropolymers in SCCO2, and studied the polymerization kinetics [75]. 

Materials. The polystyrene latex, with a mean diameter of 0.42 fim, was synthesized by emulsifier-free emulsion polymerization. Potassium persulfate was used as initiator and the surface charge that stabilizes the latex particles thus originates from sulfate radicals. The synthesis was carried out at the Department of Polymer Technology at Abo Akademi, Finland. 

Another area of microemulsion application is in the synthesis of certain polymers. The process is called emulsion polymerization, a misnomer since micelles rather than emulsion drops are the site of the polymerization reaction. Because of the commercial importance of polymers, this process has been extensively researched and is quite well understood. We only consider some highlights of the process. 

Laverty and Gardlund 65) have described the synthesis of poly(ether-b-vinyl chloride) from polyazoester prepolymers and propose, in view of the tendency of the growing polymer radicals from vinyl chloride to terminate via disproportionation, an ABA-type product. As expected, the molar masses of the products from emulsion polymerizations are greater than those from polymerizations carried out in 1,2-dichloroethane solution (Table 4.4) ... 

In the foregoing examples the synthesis of block copolymers was based on the solubility differences between two monomers, of which one is water soluble while the other is emulsified. Another polymerization technique is based on the kinetics of the emulsion polymerization. When a water emulsion of a monomer, such as styrene, is irradiated during a short time, the reaction, continues at a nearly steady rate until practically all the monomer is used up. If a second monomer is then added, it will polymerize, being initiated by the radicals occluded in the polymer particles. Although in this case also the yields of block copolymers are low, nevertheless the physical properties of the final product are markedly different from those of statistical copolymers (4, 5, 151, 176). 

With the advent of advanced characterization techniques such as multiple detector liquid exclusion chromatography and - C Fourier transform nuclear magnetic resonance spectroscopy, the study of structure/property relationships in polymers has become technically feasible (l -(5). Understanding the relationship between structure and properties alone does not always allow for the solution of problems encountered in commercial polymer synthesis. Certain processes, of which emulsion polymerization is one, are controlled by variables which exert a large influence on polymer infrastructure (sequence distribution, tacticity, branching, enchainment) and hence properties. In addition, because the emulsion polymerization takes place in an heterophase system and because the product is an aqueous dispersion, it is important to understand which performance characteristics are influended by the colloidal state, (i.e., particle size and size distribution) and which by the polymer infrastructure. 

I. J. Synthesis and characterization of exfoliated poly(styrene-co-methyl methacrylate)/clay nanocomposites via emulsion polymerization with AMPS, Polymer (2003), 44(20), 6387-6395. 

The process of miniemulsion allows in principle the use of all kinds of monomers for the formation of particles, which are not miscible with the continuous phase. In case of prevailing droplet nucleation or start of the polymer reaction in the droplet phase, each miniemulsion droplet can indeed be treated as a small nanoreactor. This enables a whole variety of polymerization reactions that lead to nanoparticles (much broader than in emulsion polymerization) as well as to the synthesis of nanoparticle hybrids, which were not accessible before. 

Glukhikh V, Graillat C, Pichot C (1987) Inverse emulsion polymerization of acrylamide. II. Synthesis and characterization of copolymers with methacrylic acid. J Polym Sci Polym Chem Ed 25(4) 1127-1161... 

Free-radical polymerization is the most widely used process for polymer synthesis. It is much less sensitive to the effects of adventitious impurities than ionic chain-growth reactions. Free-radical polymerizations are usually much faster than those in step-growth syntheses, which use diFFereiit monomers in any case. Chapter 7 covers emulsion polymerization, which is a special technique of free-radical chain-growth polymerizations. Copolymerizalions are considered separately in Chapter 8. This chapter focuses on the polymerization reactions in which only one monomer is involved. 

The latexes upon which this industry developed were natural rubber and polychloroprene for solvent resistance. However, technology is advancing to permit penetration of carboxylated nitrile latex for optimized solvent resistance and tougher abrasion resistance. Among the competition to latexes in this field are poly(vinyl chloride) plastisols. As technology develops in producing small particle size latexes from polymers whose synthesis is loo water-sensitive for emulsion polymerization, the dipped goods industry will quickly convert to their utilization from the solvent-based cements of these polymers now employed Prime candidates include butyl rubber, EPDM, hypalon, and vlton. 

Araki et at. (1967, 1969) carried out a more systematic study of the kinetics and other features of the y-iniliated emulsion polymerization of vinyl acetate using sodium lauryl sulfate as the emulsifier. This system had been thoroughly investigated with potassium persulfate as the initiator (Litt et cL. 1960,1970). Some post ei cts have been observed with vinyl acetate, particularly above 50% conversion (Friis, 1973 Sunardi, 1979). These effects had been used by Allen cr at. (1960,1962) for the possible synthesis of block and graft polymers and will be described later in this chapter. The half-life of the radicals in a vinyl acetate latex polymerization was determinad by Hummel et at. (1969) as 0.8 min at 53.8% conversion. Araki et fll. (1967, 1969) determined all the normal rate dependencies and included some seeded latex studies. Their results and those of other investigators are summarized in Table II together with those found with potassium persulfate initiation and those predicted by the Smith-Ewart Case 2 theory. The... 

We now know that emulsion polymerization is not just another polymer synthesis method and that the complexity of the interactions, whether chemical or physical, must he considered before any control is possiUe over the outcome of the reaction. The creation and nucleation of particles, for example, is not necessarily and simply explained by the presence or or absence of micelles, but needs the understanding of interactions of all the ingredients present. Variables such as hydrophilic and hydrophobic associations or repulsions, polarity of the monomers, chemical structure of the surfactants, have to lx taken into account. 

Silanes can be polymerized into the backbone of a polymer during its synthesis [6]. Emulsion polymerization of methacryloxyalkyl or vinyl functional organosilanes has been shown to be a particularly useful method of incorporating a crosslinking silane into a waterborne system. Subsequent to reaction of the methacryl or vinyl functionality, the alkoxy groups are left available either to react with a substrate or filler, or to crosslink upon film formation. 

Latex is a dispersion of polymer particles in a liquid medium, where the particles will remain suspended indefinitely. This property means that latices are colloidal dispersions. By nature of its origin, latex is classified into natural latex for dispersions obtained from plants, and synthetic latex for dispersions that are man made, typically by a process called emulsion polymerization. Blackley discusses a number of further classifications including artificial latex for dispersions in which the polymer is dispersed after synthesis, and modified latex where a chemical modification of existing latex is made. 

Emulsion polymerization intercalation is an alternative method of PCN synthesis. This method is similar to in situ polymerization, but has several differences and limitations. In the emulsion polymerization method, micelle helps the polymer to be monodisperse, yet the micelles are limited in their ability to penetrate into the layer. Nonetheless, this method is attractive because of its use of a micelle as a targeted material, which helps the monomer or prepolymer to penetrate into the silicate layers. 

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. 

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