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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 following formula (A-2a) or (A-2b) while the polymer may be crosslinked within the molecule or between molecules with these acid labile groups. 

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Herein R 40 and R 41 each are hydrogen or a straight, branched or cyclic C$_{1 }$-Cg alkyl group, or R$^{40 }$and R 41 , taken together, may form a $^{rin}$8 with the carbon atom to which they are attached, and R 4 and R$^{41 }$are straight or branched C$_{1 }$-Cg alkylene groups when they form a ring. R 42 is a straight, branched or cyclic C$_{1 }$-C$_{10 }$alkylene group. Each of bl and dl is O or an integer of 1 to 10, preferably O or an integer of 1 to 5, and cl is an integer of 1 to 7. "A" is a (cl+l)-valent aliphatic or alicyclic saturated hydrocarbon group, aromatic hydrocarbon group or heterocyclic 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, carbonyl moieties or fluorine atoms. "B" is ----CO-O-, -NHCO› O- or -NHCONH-. 

Preferably, "A" is selected from divalent to tetravalent, straight, branched or cyclic C$_{1 }$-C$_{20 }$alkylene, alkyltriyl and alkyltetrayl groups, and CcC$_{30 }$ arylene groups, which may be separated by a heteroatom or in which some carbon› bonded hydrogen atoms may be substituted by hydroxyl, carboxyl, acyl moieties or halogen atoms. The subscript cl is preferably an integer of 1 to 3. 

The crosslinking acetal groups of formulae (A-2a) and (A-2b) are exemplified by the following formulae (A-2)-70 through (A-2)-77. 

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