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[0087] In formula (AL-3), RL 5 , RL 6 and Rn are each independently a C$_{1 }$-C$_{20 }$hydrocarbyl group which may con› tain a heteroatom such as oxygen, sulfur, nitrogen or fluo› rine. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C$_{1 }$-C$_{20 }$ alkyl groups and C$_{2}$-C$_{20 }$ alkenyl groups. A pair of RL $^{5 }$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. 

[0088] Examples of the group having formula (AL-3) include tert-butyl, 1,1-diethylpropyl, 1-ethylnorbomyl, 1-methylcyclohexyl, 1-methylcyclopentyl, 1-ethylcyclopen› tyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, and tert› pentyl. 

[0089] 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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