or alkoxy group each with one to six carbon atoms which may be substituted by one to three halogen atoms, or a cycloaliphatic alkyl group, or an aryl or aryloxy group each with six or 10 carbon atoms which may be substituted up to 3 times by halogen atoms and/or alkyl or alkoxy groups with one to six carbon atoms, R' is a hydrogen atom or a methyl group, X is an oxygen atom or an imino group, A i