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Examples of the monomer from which the recurring unit (b2) is derived are shown below, but not limited thereto. R 5 and R 6 are as defined above. 

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The acid labile groups represented by R 4 and R 6 may be selected from a variety of such groups. The acid labile groups may be the same or different and preferably include groups of the following formulae (A-1) to (A-3). 

In formula (A-1), RL 1 is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in which each alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group of formula (A-3). Al is an integer of Oto 6. 

Exemplary tertiary alkyl groups are t-butyl, t-pentyl, 1,1-diethylpropyl, 1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethy lcyclohexy 1, 1-buty lcyclohexyl, 1-ethy 1-2-cyclopen› tenyl, 1-ethy 1-2-cyclohexeny 1, and 2-methy 1-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl, triethylsi- lyl, and dimethyl-t-butylsilyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and 5-methyl-2-oxooxolan-5-yl. 

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-continued 

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(A-1) 

(A-2) 

(A-3) 

