Patent ID: 8513445

Claim:
A compound having formula IA or IB: wherein: W 1 and W 2 independently are —(CR a R b ) m ; Z 1 and Z 2 independently are selected from the group consisting of O, S, and a covalent bond; L, at each occurrence, independently is an electron-withdrawing group; R a and R b , at each occurrence, independently are selected from the group consisting of H, a C 1-20 alkyl group, and a C 1-20 haloalkyl group; R 1 , R 1′ , R 1″ , R 2 , R 2′ , and R 2″ independently are selected from the group consisting of H, a C 1-20 alkyl group, a C 2-20 alkenyl group, and a C 1-20 haloalkyl group, wherein at least two of R 1 , R 1′ , and R 1″ and at least two of R 2 , R 2′ , and R 2″ are selected from a C 1-20 alkyl group, a C 2-20 alkenyl group, and a C 1-20 haloalkyl group; m, at each occurrence, independently is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and n is 0, 1, 2, 3, 4, 5, 6, 7 or 8.