Preferred ester reaction products have the general formula A: ##STR1## wherein R4 is selected from the group consisting of hydrogen, halogen, hydroxyl, C1 to C8 alkyl and C1 to C8 alkoxy, R5 is a direct bond or a C1 to C20 organic radical which may incorporate another phenol or aliphatic hydroxyl, ester, ether and/or carbonate group in its structure, R6 is hydrogen or a C1 to C20 organic radical o