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The acid labile group R $^{2 }$in recurring units (al) may be a group having the general formula (A-3)-26. 

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Herein R 26 - 1 and R 26 - 2 each are hydrogen, a C$_{1}$-C$_{4 }$ alkyl, alkoxy, alkanoyl or alkoxycarbonyl, hydroxyl, nitro, C$_{6}$-C$_{10 }$ aryl, halogen or cyano group, R is as defined above, and m26 and n26 are an integer of 1 to 4. 

Examples of the monomer from which recurring units (al) having an acid labile group of formula (A-3)-26 substituted thereon are derived are shown below. 

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