Feb.4,2021  31  US 2021/0033971 Al  (AL-2)-77  [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.  (AL-3)-1  (AL-3)-2  (AL-3)-3  (AL-3)-4  (AL-3)-5  RL14  6  (AL-3)-6  (AL-3)-13  -continued  -continued  (AL-3)-7  (AL-3)-8  (AL-3)-9  (AL-3)-10  (AL-3)-11  (AL-3)-12 