Abstract: A silsesquioxane of formula: (R1SiO1,5)x(R2SiO1,5)y(R3SiO1,5)z, wherein x?1, y?1, z?1, and x+y+z=6, 8, 10 or 12. R1 is L1-phthalimide, wherein L1 is a residue selected from the group consisting of saturated or unsaturated C1-C8 hydrocarbon radicals which may be straight, branched or cyclic; and substituted or non-substituted arylene; wherein the carbon chains of said residues optionally include one or more of the elements oxygen and nitrogen; and the phthalimide is optionally substituted by one or more halogen, C1-C6 alkyl, —COOH, —OH or —NO2. R2 is a residue selected from the group consisting of saturated or unsaturated C1-C18 hydrocarbon radicals which may be straight, branched or cyclic; wherein the carbon chains of said residues optionally include one or more oxygens and are optionally substituted by one or more halogens.