INVERSE EMULSION POLYMERISATION

Villarroya, S., Thurecht, K.J., and Howdle, S.M. 2008. HRP-mediated inverse emulsion polymerisation of acrylamide in supercritical carbon dioxide. Green Chemistry, 10 863-67. 

Villarroya, S., Thurecht, K.J., and Howdle, S.M. (2008) HRP-mediated inverse emulsion polymerisation of acrylamide in supercritical carbon dioxide. Green Chem., 10 (8), 863-867. Schomberg, D.S., Salzman, M., and Stephan, D. (1993) Enzyme Handbook vol. 7, Springer-Verlag, Berlin Heidelberg, pp. 1-6. 

It is noteworthy that each particle is covered at the end of synthesis both by the hydrophilic fragment resulting from decomposition of the initiator, e.g. sulphate groups, and by the surfactant. Both entities participate in the stability of the colloidal suspension. Emulsion polymerisation of a hydrophobic monomer in aqueous medium is sometimes referred as oil-in-water (o/w), whereas emulsion polymerisation of a hydrophilic monomer, e.g. an acrylamide, in a non-polar organic solvent is referred to as inverse emulsion polymerisation or water-in-oil (w/o). More details about the use of nanospheres for drug delivery can be found in Section 4.4.6. 

Ruckenstein and Sun [89] have used inverted emulsion polymerisation for the synthesis of PANI rubber composites using an isooctane-toluene mixture and water to form the emulsion and using ammonium persulfate as the oxidant. Inverse emulsion polymerisation consists of an aqueous solution of the monomer, which is emulsified in a non-polar organic solvent and the polymerisation is initiated with an oil-soluble initiator. The reaction is carried out in a heterogeneous system in which the reaction takes place in a large number of reaction loci dispersed in a continuous external phase. 

Inverse (or water-in-oil) emulsions (315, 401) are emulsions in which an aqueous phase is dispersed within a continuous organic phase. This system is essentially the inverse of a conventional emulsion, hence the name inverse emulsion. The organic phase is typically an inert hydrocarbon (such as mixed xylenes or low-odour kerosenes), and the aqueous phase contains a water-soluble monomer such as acrylamide (268). The aqueous phase may be dispersed as discrete droplets or as a bicontinuous phase (335), depending upon the formulation and conditions of the inverse emulsion. The hydrophilic-lipophilic balance (HLB) value of the stabiliser determines the form and stability of an inverse emulsion, with HLB values of less than 7 being appropriate for inverse emulsions. Steric stabilisers such as the Span , Tween , and Plutonic series of nonionic surfactants are usually used in preparing inverse emulsions. Inverse emulsions, suspensions, miniemulsions (199), and microemulsions have been prepared, primarily as a function of the stabiliser concentration. Commercial products produced by inverse emulsion polymerisation include polyacrylamide, a water-soluble polymer used extensively as a thickener. 

Journal of Applied Polymer Science 68, No. 13, 27th June 1998, p.2169-74 ONE-STEP PREPARATION OF ELECTRORHEOLOGICAL SUSPENSION CONTAINING POLY(LITfflUM ACRYLATE) VIA INVERSE EMULSION POLYMERISATION AND STUDY OF ITS ELECTRORHEOLOGICAL EFFECT... 

A rapid and low cost method was developed for direct analysis of residual monomer concentration of acrylamide from inverse-emulsion reactions. Inverse-emulsion polymerisations involve the dispersion of a water-soluble monomer in aqueous solution in a continuous organic phase. The addition of a low-medium hydrophilic-lyophilic balance steric stabiliser and continuous agitation is required to maintain emulsification. 19 refs. 

As described earlier in the section on bead or suspension polymers (Section 3.3.1.2), a solution of monomer(s) is prepared in water and then mixed into a low to medium viscosity non-volatile oil phase. In this process, which is often referred to as an inverse emulsion polymerisation technique, surfactants which promote the formation of water-in-oil emulsions are commonly used. These would usually be materials with an HLB (hydrophihc-lipophilic balance) value in the range 4—7, an example of which is sorbitan mono-oleate. In order to achieve the desired droplet particle size of a maximum around 1 pim prior to polymerisation, high shear homogenisers are used to assist the formation of such very small... 

The book is focusing on emulsion polymerisation in combination with both conventional and controlled radical polymerisation. Except for miniemulsion polymerisation, more exotic techniques, such as inverse emulsion polymerisation, microemulsion polymerisation and dispersion polymerisation are not covered. Chapter 1 gives a historic overview of the understanding of emulsion polymerisation, while also focusing on the solution of the... 

An emulsion polymerisation system comprises water, an initiator (usually water soluble), a water-insoluble monomer and a colloidal stabiliser, which may be added or maybe formed in situ. The main locus of polymerisation is within the monomer-swollen latex particles, which are either formed at the start of polymerisation or may be added initially (in which case one has a seeded emulsion polymerisation). The term emulsion polymerisation is a misnomer (arising for historical reasons the process was originally developed with the aim of polymerising emulsion droplets, although, in fact, this does not occur). The starting emulsion is not thermodynamically stable. An inverse emulsion polymerisation is one where the continuous phase is organic in combination with an aqueous discrete phase containing a water-soluble monomer (e.g. acrylamide). Two variants of emulsion polymerisation are... 

Equation (4) clearly shows that the number average degree of polymerisation Xn is inversely proportional to the reaction rate Rp, meaning that, in radical chain polymerisation high reaction rates are linked to low molecular masses and vice versa. One way to avoid this dilemma is to use emulsion polymerisation where the lifetime of a radical (i.e., the "kinetic" chain length) is independent of... 

This was shown to good effect in an experiment [22] carried out to prepare a series of cationic acrylamide copolymers (60/40 weight ratio) as inverse emulsion polymers using identical polymerisation conditions, in which only the concentration of cross-linking monomer was varied. Subsequent determination of intrinsic viscosity values for this set of polymers showed the results in Table 3.1. 

Several methods have been reported for the synthesis of microgel particles, these include emulsion polymerisation (EP) [5, 6], inverse EP [7], living free-radical polymerisation [8,9] and synthesis by radiation [10,11]. 

Emulsion polymerisation is normally undertaken by the resin manufacturer. Inversion can be undertaken in house . Acid (or amine) rich resins can be purchased and subsequently inverted by the formulator. Some people refer to these inverted dispersions as water reducible resins. 

Inverse opals are formed by the use of micro- or nanospheres to template a structure containing spherical cavities. One way of doing this is to use monodisperse latex spheres. These latex spheres are prepared by slow addition of an aqueous precursor solution into a reservoir of hydrophobic silicone liquid, forming emulsion droplets. The size of the droplets is controlled by the concentration of the aqueous latex, the speed at which the suspension is stirred and ratio between the silicone liquid and latex. Polymerisation results in latex spheres of well defined size of the order of a few hundred nanometers, and spherical shape. As the concentration of the latex spheres increases to its critical concentration... 

High molecular weight water soluble polymers are produced commercially in the largest volumes as either finely divided solids or as inverse (water-in-oil) emulsions (which can be optionally dehydrated to provide a higher concentration product). Precipitation polymerisation in electrolyte solution to provide so-called water-in-water polymers is also well known. 

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