US 10,005,868 B2  41  42  In the above formulae, each  RL 37  may be the same or  different, and represents a linear, branched, or cyclic alkyl  group having  1  to  10  carbon atoms or an aryl group having  6 to 20 carbon atoms, and  RL $^{38 }$represents a hydrogen atom  or a linear, branched, or cyclic alkyl group having  1  to  10  carbon atoms.  Each  RL $^{39 }$may be the same or different, and represents a  linear, branched, or cyclic alkyl group having 2 to  10  carbon  atoms or an aryl group having 6 to 20 carbon atoms.  Al is as defined above.  In the formula (A-2),  RL $^{31 }$and  RL $^{32 }$represent a hydrogen  atom or a linear, branched, or cyclic alkyl group having  1  to  18, preferably  1  to  10  carbon atoms. Illustrative examples  thereof include a methyl group, an ethyl group, a propyl  group, an isopropyl group, a n-butyl group, a sec-butyl  group, a tert-butyl group, a cyclopentyl group, a cyclohexyl  group, a 2-ethylhexyl group, and a n-octyl group.  RL $^{33 }$represents a monovalent hydrocarbon group having 1  to 18, preferably  1  to  10  carbon atoms, and optionally  containing a heteroatom such as an oxygen atom. For  example, there may be mentioned a linear, branched, or  cyclic alkyl group and a group in which a part of hydrogen  atoms in these groups is substituted with a hydroxyl group,  an alkoxy group, an oxo group, an amino group, an alky› lamino group, or the like. Illustrative examples thereof  include the following substituted alkyl groups.  RL31  and  RL32, RL3I  and  RL33’  and  RL32  and  RL33  may be  bonded to form a ring together with the carbon atoms to  which these groups are bonded; and when the ring is formed,  RL3 1 ,  RL 32 ,  and  RL $^{33 }$that participate in the ring formation  each represent a linear or branched alkylene group having  1  to 18, preferably  1  to  10  carbon atoms. The carbon number  in the ring is preferably 3 to  10,  particularly preferably  4  to  10.  Among the acid-labile groups shown by the formula  (A-2), illustrative examples of the linear or branched one  include groups of the following formulae (A-2)-1 to (A-2)- 35.  -continued  (A-1)-9  (A-1)-10  (A-2)-1  (A-2)-2  (A-2)-3  (A-2)-4  (A-2)-5  (A-2)-6  (A-2)-7  (A-2)-8  (A-2)-9  (A-2)-10  (A-2)-11  (A-2)-12  (A-2)-13  (A-2)-14  (A-2)-15  -t-o--(J  (A-2)-16  -t-o-o  (A-2)-17 