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(A-2)-66 

(A-2)-67 

(A-2)-68 

(A- 2 )- 69 

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. 

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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-2a) 

(A-2b) 

(A-2)-70 

(A-2)-71 

(A-2)72 

(A-2)-73 

