Seeded radical polymerisation

It is possible to obtain a bimodal distribution of final particles median diameter (distribution with two maxima), by seeded radical polymerisation. For example, if a polymer polyol having particle diameter of 0.3-0.6 pm is added to the poly ether before the radical polymerisation, after the normal polymerisation of the vinylic monomers, polymer polyols with a bimodal distribution of particles are obtained. As a general rule, a bimodal distribution leads to lower viscosities than an unimodal distribution of particle diameters, at the same solid content [32]. This is a method to obtain high, solid polymer... 

An ab initio emulsion polymerisation involves the emulsification of one or more monomers in a continuous aqueous phase and stabilisation of the droplets by a surfactant. In a seeded emulsion polymerisation, one starts instead with a preformed seed latex. Usually, a water-soluble initiator is used to start the free-radical polymerisation. The locus of polymerisation is within the submicron polymer particles (either formed during the process or added at the start), which are swollen with monomer during the polymerisation process, and dispersed in the aqueous phase. The final product is a latex comprising a colloidal dispersion of polymer particles in water. Ab initio emulsion polymerisation differs from suspension, mini- and microemulsion polymerisations in that the particles form as a separate phase during the polymerisation process. The particle size is much smaller than those formed in a suspension 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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