SEEDED POLYMERISATION

Seeded Polymerisation after Polyvinyl Alcohol Adsorption. 

To assess the effect of an adsorbed layer of polyvinyl alcohol on the rate of polymerisation, the rates of seeded polymerisation were measured after adsorption of various grades of polyvinyl ailcohol on the seed latex. The seed latex was prepared in the same way as the latex used in the adsorption experiments. After adsorption of polyvinyl alcohol from a 0.10 % w/v solution, the concentration of the seed latex wets 0.9A5 % w/v in a 2.0 % v/v vinyl acetate solution containing 7.4 x 10" mol dm" potassium persulphate. The rates of polymerisation (the means of two to four experiments) observed at 60 C are tabulated below. 

The advantage of the low Cex RCTAs is that latexes with controlled particle size distributions using seeded polymerisations can be made. These latex particles in a second stage polymerisation can be further reacted with other monomers to make block copolymers with core-shell particle morphology or even latex particles in which the second block has functional groups, that is, reactive latexes (Monteiro de Barbeyrac, 2002). 

In this connection, different strategies are in principle possible. The first involves use of porous seeds that can be swollen or (in the case of a rigid porous seed) imbibed with the monomer mixture yielding the MIP. Subsequent polymerisation within the seeds yields a composite in beaded form containing the MIP component. The seed can be subsequently removed prior to MIP use or left in the composite. 

This method involves a combination of stepwise swelling of preformed seed particles followed by polymerisation (Fig. 6). 

A similar seeding technique can be used to prepare monodispersed polymer latex dispersions by emulsion polymerisation (see page 17). 

Monodispersed sols containing spherical polymer particles (e.g. polystyrene latexes22"24, 135) can be prepared by emulsion polymerisation, and are particularly useful as model systems for studying various aspects of colloidal behaviour. The seed sol is prepared with the emulsifier concentration well above the critical micelle concentration then, with the emulsifier concentration below the critical micelle concentration, subsequent growth of the seed particles is achieved without the formation of further new particles. 

Epoxidised oils (with isolated double bonds), such as epoxidised soybean are used as plasticisers. The natural occurrence of epoxidised fatty acids could be exploited to reduce processing costs on the pathway to polymerisation. For example, seed oils derived from Vernonia galamensis and Euphorbia lagascae both contain significant proportions (60-80%) of the epoxy acid vemolic acid, with interesting applications in greases and polyurethane applications (Turley et al., 2000). 

A larger elementary particle size can be achieved by seeding the initial emulsion system. A PVC polymer latex is introduced and the particles of the new polymer grow on the seed. A continuous emulsion polymerisation process is also used. 

The monomers, styrene, and methyl methacrylate (Aldrich) and ethyl methacrylate and n-butyl acrylate (Fluka) were purified prior to use. The crosslinking agent used in the synthesis of these semi-1-IPNs was tetraethyleneglycol dimethacrylate (Fluka). The emulsion polymerisation (90 C) was initiated with ammonium persulphate/sodium metabisulphite (both from BDH) and the resulting latex, which was prepared by a seed and feed procedure, was stabilised with sodium dioctyl sulfosuccinate (OT75 from Cyanamid). 

The concept of surface imprinting by the use of seed emulsion polymerisation... 

Metal ion-imprinted microspheres were prepared as follows [14,15]. Seed emulsion was obtained by the polymerisation of styrene, butyl acrylate and methacrylic acid in water. Divinylbenzene, butyl acrylate and water were further added to the polymerisation mixture (seed emulsion) and the emulsion was left for a defined time so that the seed microspheres became swollen. The emulsion was combined with a metal ion solution to achieve complexation between the metal ion and the carboxyl group on the surface. Then the divinylbenzene-containing emulsion was polymerised by the use of y-rays at room temperature. The micro-spheres obtained by centrifugation were washed with a hydrochloric acid solution to remove the metal ion. The microspheres obtained were then dried under vacuum. Non-imprinted microspheres (as a reference) were synthesised similarly, but without a metal ion. 

Surface rearrangement of latex (latex obtained from seeded emulsion polymerisation)... 

The technique involves first producing a seed latex by emulsifier-free emulsion polymerisation. A polystyrene latex of about 1 pva diameter is usually used. The seed particles are initially swollen using a microemulsion of a free radical initiator and a low molecular weight activating solvent , such as dibutyl phthalate, emulsified in water by sonication using sodium dodecyl sulphate as stabiliser. The seed... 

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