US 10,303,056 B2  21  22  -continued  (A-2)-66  (A-2)-67  Of the acid labile groups of formula (A-2), the cyclic ones  are, for example, tetrahydrofuran-2-yl, 2-methyltetrahydro› furan-2-yl, tetrahydropyran-2-yl, and 2-methyltetrahydropy› ran-2-yl.  Other examples of acid labile groups include those of the  formula (A-2a) or (A-2b) while the polymer may be cross› linked within the molecule or between molecules with these  acid labile groups.  (A-2a)  (A-2b)  (A-2)-68  Herein  RL 11  and  RL 12  each are hydrogen or a C$_{1 }$-Cg  straight, branched or cyclic alkyl group, or  RL 11  and  RL 12 ,  taken together, may form a ring with the carbon atom to  which they are attached, and the ring-forming pair of  RL 11  and  RL 12  is a C$_{1 }$-Cg straight or branched alkylene group.  RL $^{13 }$is a C$_{1 }$-C$_{10 }$straight, branched or cyclic alkylene group.  Each of B  1  and D 1 is an integer of  0  to  10,  preferably  0  to  5, and Cl is an integer of  1  to 7, preferably  1  to 3.  "A" is a (Cl+l)-valent aliphatic or alicyclic saturated  hydrocarbon group, aromatic hydrocarbon group or hetero› cyclic group having  1  to 50 carbon atoms, which may be  separated by a heteroatom or in which some carbon-bonded  hydrogen atoms may be substituted by hydroxyl, carboxyl,  acyl groups or fluorine atoms. Preferably, "A" is selected  from C$_{1 }$-C$_{20 }$straight, branched or cyclic alkylene, alkyltriyl  and alkyltetrayl groups, and C$_{6}$-C$_{30 }$ arylene groups. "B" is  ----CO-O-, -NHCO-O- or -NHCONH-.  The crosslinking acetal groups of formulae (A 2a) and  (A-2b) are exemplified by the following formulae (A-2)-70  through (A-2)-77.  (A-2)-70  (A-2)-71  (A-2)72  (A-2)-73  (A- 2 )- 69  CH3  I  -CH-0 