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[0088] In formula (AL-3), RL 5 , RL 6 and Rn are each independently a C$_{1 }$-C$_{20 }$ monovalent hydrocarbon group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The monovalent hydrocarbon group may be straight, branched or cyclic and examples thereof include C$_{1 }$-C$_{20 }$ alkyl groups and C$_{2}$-C$_{20 }$ alkenyl groups. A pair ofRL 5 and RL 6 , RL 5 and Rn, or RL $^{6 }$and RL $^{7 }$may bond together to form a C$_{3}$ -C$_{20 }$aliphatic ring with the carbon atom to which they are attached. 

[0089] Examples of the group having formula (AL-3) include tert-butyl, 1,1-diethylpropyl, 1-ethylnorbomyl, 1-methy lcyclohexy 1, 1-methy lcyclopenty 1, 2-(2-methy 1 )ada› manty l, 2-(2-ethyl)adamantyl, and tert-pentyl. 

[0090] Examples of the group having formula (AL-3) also include groups having the formulae (AL-3)-1 to (AL-3)-18. 

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