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Herein R$^{37 }$is each independently a straight, branched or cyclic C$_{1 }$-C$_{10 }$alkyl group or C$_{6}$-C$_{20 }$aryl group, R$^{38 }$is hydro- gen or a straight, branched or cyclic C$_{1 }$-C$_{10 }$alkyl group, R 39 is each independently a straight, branched or cyclic C$_{2}$ -C$_{10 }$ alkyl group or C$_{6}$-C$_{20 }$aryl group, and al is as defined above. 

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)-69. 

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