Furthermore, the various phenylene or cyclohexylene radicals can be substituted by methyl groups.The symbol G can represent for example, a phenyl radical optionally substituted by inert atoms, radicals or groups such as Cl, F, CH.sub.3, OCH.sub.3 and NO.sub.2.The symbol T can represent for example, an alkyl radical with 1 to 18 carbon atoms, a phenyl or cyclohexyl radical or ##STR22## wherein n is