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“Polyoxyethylene-polyoxypropylene-block copolymers, generally designated poloxamers, have the general formula HO(C2H4O)a (C3H6O)b (C2H4O)a H.
Poloxamers are manufactured in a variety of different grades which are commercially available and different with respect to molecular weight and the ratio between the number of oxyethylene units a and the number of oxypropylene units b. In the preferred embodiments of the poloxamer, the value a is substantially larger than the value b in said structural formula and the average molecular weight is above 10000. A poloxamer, which is preferred in the composition according to the invention, is available under the designation poloxamer 407, which has a molecular weight of 9840-14600 and where the number of units a is 101 and the number of units b is 56. According to a particularly preferred embodiment, poloxamer 407 is included in an amount of 13-15% by weight of the composition.
In contrast to normal polymers, a high-molecular poloxamer is readily fluid at low temperatures, but will get a highly increased viscosity at higher temperatures. Poloxamer 407 which is dispersed in water in an amount of 25%, for instance, is fluid up to about 20.degree. C. and will then transform into a stable gel, which is permanent up to about 70.degree. C., whereas a 16% solution of this poloxamer is fluid up to about 30.degree. C. and will then form a gel, which is permanent up to about 60.degree. C. At lower levels of this polymer, however, no gel is formed. Poloxamer is preferably included in an amount of at least 10% by weight of the composition and said at least one additional polymer in an amount of at least 5% by weight of the composition. Most preferably, the poloxamer is included in an amount of 10-25% by weight of the composition and said at least one additional polymer in an amount of 5-20% by weight of the composition.”
[Hoglund and Kryzaniak, US Patent 8,137,391 (3/20/2012)]
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Roger D. Corneliussen
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