| http://www.w3.org/ns/prov#value | - Suitable polyethers for the purpose of the invention, containing at least two, generally two to eight, preferably two or three hydroxyl groups are of the type known per se and may be prepared, for example, by the polymerization of tetrahydrofuran and/or epoxides such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide or epichlorohydrin, either on their own (e.g., in the presence of
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