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[0117] In formulas (L4-1) to (L4-4), the broken line denotes a bonding site and direction. RL $^{41 }$is each indepen› dently a C$_{1 }$-C$_{10 }$ monovalent hydrocarbon group. The mon› ovalent hydrocarbon group may be straight, branched or cyclic, and examples thereof include alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert› butyl, tert-pentyl, n-pentyl, n-hexyl, cyclopentyl and cyclo› hexyl. 

[0118] For formulas (L4-1) to (L4-4), there can exist stereoisomers ( enantiomers or diastereomers ). Each of for› mulae (L4-1) to (L4-4) collectively represents all such stereoisomers. When the acid labile group XA is of formula (L4), there may be contained a plurality of stereoisomers. 

[0119] For example, the formula (L4-3) represents one or a mixture of two selected from groups having the following formulas (L4-3-l) and (L4-3-2). 

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Herein RL 41 is as defined above. 

[0120] Similarly, the formula (L4-4) represents one or a mixture of two or more selected from groups having the following formulas (L4-4-1) to (L4-4-4). 

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Herein RL 41 is as defined above. 

[0121] Each of formulas (L4-1) to (L4-4), (L4-3-l) and (L4-3-2), and (L4-4-1) to (L4-4-4) collectively represents an enantiomer thereof and a mixture of enantiomers. 

[0122] It is noted that in the above formulas (L4-1) to (L4-4), (L4-3-l) and (L4-3-2), and (L4-4-1) to (L4-4-4), the bond direction is on the exo side relative to the bicyclo[2. 2.l]heptane ring, which ensures high reactivity for acid catalyzed elimination reaction (see JP-A 2000-336121). In preparing these monomers having a tertiary exo-alkyl group of bicyclo[2.2.l]heptane skeleton as a substituent group, there may be contained monomers substituted with an endo-alkyl group as represented by the following formulas (L4-1-endo) to (L4-4-endo). For good reactivity, an exo proportion of at least 50 mo! % is preferred, with an exo proportion of at least 80 mo! % being more preferred. 

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