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"Modified from M. W. Edens, in Nonionic Surfactants. Polyoxyalkylene Block Copolymers (ed. V. M. Nace), Surfactant Science Series 60, Marcel Dekker, New York, 1996, pp. 185-210.

"Modified from M. W. Edens, in Nonionic Surfactants. Polyoxyalkylene Block Copolymers (ed. V. M. Nace), Surfactant Science Series 60, Marcel Dekker, New York, 1996, pp. 185-210.

content is approximately 80% of the molecule by weight. A grid was developed by BASF to interrelate the properties of the Pluronics (Fig. 6.36a). The BASF nomenclature has been adopted by the other major supplier of polox-amers, Uniqema, who market the copolymers as the Synperonic series. The relationship between the Pluronic (and Synperonic) and poloxamer nomenclatures is shown in Table 6.9, which also gives the composition of each copolymer.

Included in Table 6.9 are examples of block copolymers of poly(oxyethylene) and poly (oxypropylene) with the general formula P„EmP„ (meroxapols). The nomenclature for these 'reverse' block copolymers uses three digits, the first two (approximately one-hundredth of the molecular weight of the poly(oxypropylene) block) separated from the third (approximately one-tenth of the weight percentage of poly(oxyethylene) in the molecule) by the letter R. For example, 25 R4 contains 40% by weight of poly(oxyethylene), and the total molecular weight of the poly (oxypropylene) blocks is approximately 2500. The properties of the Pluronic R series are interrelated using the grid shown in Fig. 6.36b.

The poloxamers are water soluble and, as might be expected from their amphiphilic structure, are also surface active. Many of the series form micelles, the properties of which have been reviewed by several authors. 16,17

Poloxamers are used as emulsifying agents for intravenous fat emulsions, as solubilising agents to maintain clarity in elixirs and syrups, and as wetting agents for antibacterials. They may also be used in ointment or suppository bases and as tablet binders or coaters.

6.6 Solubilisation

As we have seen in section 6.3, the micellar core is essentially a paraffin-like region and as such is capable of dissolving oil-soluble molecules. This process, whereby water-insoluble substances are brought into solution by incorporation into micelles, is termed solubilisation and the incorporated substance is referred to as the solubilisate. The subject of solubilisation has been reviewed extensively1,18 and it is only possible in this book to give an outline of this phenomenon.

6.6.1 Determination of maximum additive concentration

The maximum amount of solubilisate that can be incorporated into a given system at a fixed

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