% by weight allyl ether comprising a fatty chain of formula (I)in which R' is H or CH.sub.3, B is an ethylenoxy radical, n is zero or is an integer ranging from 1 to 100, and R is a hydrocarbon radical selected from alkyl and cycloalkyl radicals, having from 8 to 30 carbon atoms, and from 0 to 1% of acrosslinking agent.12.