-continued  26  US 9,152,050 B2  25  In formula (A-2), RL$^{31 }$and  RL $^{32 }$are hydrogen or straight,  branched or cyclic alkyl groups of 1 to 18 carbon atoms,  preferably 1 to 10 carbon atoms. Exemplary alkyl groups  include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,  tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, and n-oc- tyl.  RL $^{33 }$is a monovalent hydrocarbon group ofl to 18 carbon  atoms, preferably 1 to 10 carbon atoms, which may contain a  heteroatom such as oxygen, examples of which include  straight, branched or cyclic alkyl groups and substituted  forms of such alky I groups in which some hydrogen atoms are  replaced by hydroxyl, alkoxy, oxo, amino, alkylamino or the  like. Illustrative examples of the substituted alkyl groups are  shown below.  A pair ofRL$^{31 }$and  RL 32 ,  RL$^{31 }$and  RL 33 ,  or  RL $^{32 }$and  RL 33  may bond together to form a ring with the carbon and oxygen  atoms to which they are attached. Each ofRL 31 ,  RL $^{32 }$and  RL 33  is a straight or branched alkylene group of 1 to 18 carbon  atoms, preferably 1 to 10 carbon atoms when they form a ring,  while the ring preferably has 3 to 10 carbon atoms, more  preferably 4 to 10 carbon atoms.  Examples of the acid labile groups of formula (A-1)  include  tert-butoxycarbony I,  tert-butoxycarbony lmethy I,  tert-amy loxycarbonyl, tert-amy loxycarbonylmethy I, 1, 1-di› ethylpropy loxycarbony I,  1, 1-diethy lpropy loxycarbonylm› ethyl,  1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopenty- loxycarbony !methyl,  1-ethy 1-2-cyclopenteny loxycarbony I,  1-ethy 1-2-cyclopenteny loxycarbonylmethyl,  1-ethoxy› ethoxycarbony lmethy l,  2-tetrahydropyranyloxycarbonyl› methyl, and 2-tetrahydrofuranyloxycarbonylmethyl groups.  Also included are substituent groups having the formulae  (A-1)-1 to (A-1)-10.  Herein RL$^{37 }$is each independently a straight, branched or  cyclic C$_{1 }$-C$_{10 }$alkyl group orC$_{6}$-C$_{20 }$aryl group. RL$^{33 }$is hydro› gen or a straight, branched or cyclic C$_{1 }$-C$_{10 }$alkyl group.  RL 39  is each independently a straight, branched or cyclic C$_{2}$-C$_{10 }$ alkyl group or C$_{6}$-C$_{20 }$aryl group. Al is an integer of Oto 6.  Of the acid labile groups of formula (A-2), the straight and  branched ones are exemplified by the following groups hav› ing formulae (A-2)-1 to (A-2)-35.  (A-1)-2  j,cH,),-yO{’Rml  .  l  O  RL37  (A-1)-3  t"’’’Yotf"  l  (A-2)-1  (A-2)-2  (A-2)-3  (A-2)-4  (A-1)-10  (A-1)-9  (A-1)-8  (A-1)-7  (A-1)-6  (A-1)-5  (A-1)-4 