R1???CH???C(R2)C(O)???X1???X2???X3???C(O)???CH2???C(O)???R3???(1) where R1 is a hydrogen or halogen; R2 is a hydrogen, halogen, C1-C6 alkylthio group, or C1-C6 alkyl group; R3 is a C1-C6 alkyl group; X1 and X3 are independently O, S, or a group of the formula ???N(R???)???, in which R??? is a C1-C6 alkyl group; X2 is a C1-C12 alkylene group or C3-C12 cycloalkylene group; about 0.05 to about 20 wei