US 10,303,056 B2  23  24  -continued  (A-3)-1  (A-3)-2 55  (A-3)-3  (A-3)-4  -continued  (A-3)-5  (A-3)-6  (A-3)-7  (A-3)-8  In formula (A-3),  RL 5 ,  RL 6  and RL 7  are each indepen- dently a monovalent hydrocarbon group, typically a C$_{1 }$-C$_{20 }$ straight, branched or cyclic alkyl group or C$_{2}$-C$_{20 }$ straight,  branched or cyclic alkenyl group, which may contain a  heteroatom such as oxygen, sulfur, nitrogen or fluorine. 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.  Exemplary groups of formula (A-3) include tert-butyl,  triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl, 1-eth- ylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adaman› tyl, and tert-pentyl.  Other exemplary groups of formula (A-3) include those of  the kg formulae (A-3)-1 to (A-3)-18.  (A-2)-74  (A-2)-75  c~  c~  I  I  -cH-o-cH,m,o’t:YocH,cH, 1 -o-cH- y  CH3  OCH2CH2-0-CH- (A-2)-76  (A-2)-77  ~RL14)  \~L16 