, ethyl or isopropyl radical; or it can be joined with R5 to form a saturated or unsaturated, 5 or 6 membered rings as described above; R7 is preferably a linear or branched, saturated or unsaturated C1-C20-alkyl radical, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table of the Elements; preferably a C1-C10-alkyl radical; more preferably R7 is a methyl or ethyl radi