, C1 to C8 alkyl and C1 to C8 alkoxy, R5 is a direct bond or a C1 to C20 organic radical, R6 is hydrogen or a C1 to C20 organic radical which may form with R7 part of a 5 or 6 carbon atom cyclic ring structure, R7 is CH2 R8 wherein R8 is selected from the group consisting of hydroxy, OR9, OOCR10 and R11 wherein R9 is a primary or secondary aliphatic group containing 3 to 20 carbon atoms or an arom