This invention provides compounds represented by the structure of the general formula (A):wherein L is a lipid or a phospholipid, Z is either nothing, ethanolamine, serine, inositol, choline, or glycerol, Y is either nothing or a spacer group ranging in length from 2 to 30 atoms, X is a polymer and n is a number from 1 to 1000, wherein any bond between L, Z, Y and X is either an amide or an esteric bond.