. . . . "wherein each occurrence of R6 is independently H or C1-C12 hydrocarbyl, each R5 is the same or different, and is a halogen, cyano, nitro, C1-C8 alkylthio, C1-C8 alkyl, C1-C8 alkoxy, C2-C8 alkenyl, C2-C8 alkenyloxy group, C3-C8 cycloalkyl, C3-C8 cycloalkoxy, C6-C10 aryl, C6-C10 aryloxy, C7-C12 aralkyl, C7-C12 aralkoxy, C7-C12 alkaryl, or C7-C12 alkaryloxy, b is 1 to 8, a is independently 0, 1, 2, 3" .