| 摘要 |
A compound of formula IV: wherein R1, R2, and R3 are, independently at each occurrence, a C1-C20 aliphatic radical, a C3-C20 aromatic radical, or a C3-C20 cycloaliphatic radical; Ar is heteroaryl, aryl, alkyl or cycloalkyl; b and c are, independently at each occurrence, an integer ranging from 0-4; a is an integer ranging from 0-3; and n is an integer ranging from 2 to 4.
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